inc/qcbor/UsefulBuf.h

/* =========================================================================
 * Copyright (c) 2016-2018, The Linux Foundation.
 * Copyright (c) 2018-2024, Laurence Lundblade.
 * Copyright (c) 2021, Arm Limited. All rights reserved.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 *       copyright notice, this list of conditions and the following
 *       disclaimer in the documentation and/or other materials provided
 *       with the distribution.
 *     * Neither the name of The Linux Foundation nor the names of its
 *       contributors, nor the name "Laurence Lundblade" may be used to
 *       endorse or promote products derived from this software without
 *       specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * ========================================================================= */

/*============================================================================
 FILE:  UsefulBuf.h

 DESCRIPTION:  General purpose input and output buffers

 EDIT HISTORY FOR FILE:

 This section contains comments describing changes made to the module.
 Notice that changes are listed in reverse chronological order.

 when         who             what, where, why
 --------     ----            --------------------------------------------------
 08/14/2024   llundblade      Add UsefulOutBuf_RetrieveOutputStorage().
 08/13/2024   llundblade      Add UsefulInputBuf_RetrieveUndecodedInput().
 08/08/2024   llundblade      Add UsefulOutBuf_SubString().
 10/05/2024   llundblade      Add Xxx_OffsetToPointer.
 28/02/2024   llundblade      Rearrange UsefulOutBuf_Compare().
 1/7/2024     llundblade      Add UsefulInputBuf_Compare().
 19/11/2023   llundblade      Add UsefulOutBuf_GetOutput().
 19/11/2023   llundblade      Add UsefulOutBuf_Swap().
 19/11/2023   llundblade      Add UsefulOutBuf_Compare().
 19/12/2022   llundblade      Document that adding empty data is allowed.
 4/11/2022    llundblade      Add GetOutPlace and Advance to UsefulOutBuf.
 9/21/2021    llundbla        Clarify UsefulOutBuf size calculation mode
 8/8/2021     dthaler/llundbla Work with C++ without compiler extensions
 5/11/2021    llundblade      Improve comments and comment formatting.
 3/6/2021     mcr/llundblade  Fix warnings related to --Wcast-qual
 2/17/2021    llundblade      Add method to go from a pointer to an offset.
 1/25/2020    llundblade      Add some casts so static anlyzers don't complain.
 5/21/2019    llundblade      #define configs for efficient endianness handling.
 5/16/2019    llundblade      Add UsefulOutBuf_IsBufferNULL().
 3/23/2019    llundblade      Big documentation & style update. No interface
                              change.
 3/6/2019     llundblade      Add UsefulBuf_IsValue()
 12/17/2018   llundblade      Remove const from UsefulBuf and UsefulBufC .len
 12/13/2018   llundblade      Documentation improvements
 09/18/2018   llundblade      Cleaner distinction between UsefulBuf and
                              UsefulBufC.
 02/02/18     llundbla        Full support for integers in and out; fix pointer
                              alignment bug. Incompatible change: integers
                              in/out are now in network byte order.
 08/12/17     llundbla        Added UsefulOutBuf_AtStart and UsefulBuf_Find
 06/27/17     llundbla        Fix UsefulBuf_Compare() bug. Only affected
                              comparison for < or > for unequal length buffers.
                              Added UsefulBuf_Set() function.
 05/30/17     llundbla        Functions for NULL UsefulBufs and const / unconst
 11/13/16     llundbla        Initial Version.

 =============================================================================*/

#ifndef _UsefulBuf_h
#define _UsefulBuf_h


/*
 * Endianness Configuration
 *
 * This code is written so it will work correctly on big- and
 * little-endian CPUs without configuration or any auto-detection of
 * endianness. All code here will run correctly regardless of the
 * endianness of the CPU it is running on.
 *
 * There are four C preprocessor macros that can be set with #define
 * to explicitly configure endianness handling. Setting them can
 * reduce code size a little and improve efficiency a little.
 *
 * Note that most of QCBOR is unaffected by this configuration.  Its
 * endianness handling is integrated with the code that handles
 * alignment and preferred serialization. This configuration does
 * affect QCBOR's (planned) implementation of integer arrays (tagged
 * arrays) and use of the functions here to serialize or deserialize
 * integers and floating-point values.
 *
 * Following is the recipe for configuring the endianness-related
 * #defines.
 *
 * The first option is to not define anything. This will work fine
 * with all CPUs, OS's and compilers. The code for encoding integers
 * may be a little larger and slower.
 *
 * If your CPU is big-endian then define
 * USEFULBUF_CONFIG_BIG_ENDIAN. This will give the most efficient code
 * for big-endian CPUs. It will be small and efficient because there
 * will be no byte swapping.
 *
 * Try defining USEFULBUF_CONFIG_HTON. This will work on most CPUs,
 * OS's and compilers, but not all. On big-endian CPUs this should
 * give the most efficient code, the same as
 * USEFULBUF_CONFIG_BIG_ENDIAN does. On little-endian CPUs it should
 * call the system-defined byte swapping method which is presumably
 * implemented efficiently. In some cases, this will be a dedicated
 * byte swap instruction like Intel's bswap.
 *
 * If USEFULBUF_CONFIG_HTON works and you know your CPU is
 * little-endian, it is also good to define
 * USEFULBUF_CONFIG_LITTLE_ENDIAN.
 *
 * if USEFULBUF_CONFIG_HTON doesn't work and you know your system is
 * little-endian, try defining both USEFULBUF_CONFIG_LITTLE_ENDIAN and
 * USEFULBUF_CONFIG_BSWAP. This should call the most efficient
 * system-defined byte swap method. However, note
 * https://hardwarebug.org/2010/01/14/beware-the-builtins/.  Perhaps
 * this is fixed now. Often hton() and ntoh() will call the built-in
 * __builtin_bswapXX()() function, so this size issue could affect
 * USEFULBUF_CONFIG_HTON.
 *
 * Last, run the tests. They must all pass.
 *
 * These #define config options affect the inline implementation of
 * UsefulOutBuf_InsertUint64() and UsefulInputBuf_GetUint64().  They
 * also affect the 16-, 32-bit, float and double versions of these
 * functions. Since they are inline, the size effect is not in the
 * UsefulBuf object code, but in the calling code.
 *
 * Summary:
 *   USEFULBUF_CONFIG_BIG_ENDIAN -- Force configuration to big-endian.
 *   USEFULBUF_CONFIG_LITTLE_ENDIAN -- Force to little-endian.
 *   USEFULBUF_CONFIG_HTON -- Use hton(), htonl(), ntohl()... to
 *     handle big and little-endian with system option.
 *   USEFULBUF_CONFIG_BSWAP -- With USEFULBUF_CONFIG_LITTLE_ENDIAN,
 *     use __builtin_bswapXX().
 *
 * It is possible to run this code in environments where using floating point is
 * not allowed. Defining USEFULBUF_DISABLE_ALL_FLOAT will disable all the code
 * that is related to handling floating point types, along with related
 * interfaces. This makes it possible to compile the code with the compile
 * option -mgeneral-regs-only.
 */

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN) && defined(USEFULBUF_CONFIG_LITTLE_ENDIAN)
#error "Cannot define both USEFULBUF_CONFIG_BIG_ENDIAN and USEFULBUF_CONFIG_LITTLE_ENDIAN"
#endif


#include <stdint.h> /* for uint8_t, uint16_t.... */
#include <string.h> /* for strlen, memcpy, memmove, memset */
#include <stddef.h> /* for size_t */


#ifdef USEFULBUF_CONFIG_HTON
#include <arpa/inet.h> /* for htons, htonl, htonll, ntohs... */
#endif

#ifdef __cplusplus
extern "C" {
#if 0
} /* Keep editor indention formatting happy */
#endif
#endif

/**
 * @file UsefulBuf.h
 *
 * The goal of this code is to make buffer and pointer manipulation
 * easier and safer when working with binary data.
 *
 * The @ref UsefulBuf, @ref UsefulOutBuf and @ref UsefulInputBuf
 * structures are used to represent buffers rather than ad hoc
 * pointers and lengths.
 *
 * With these it is possible to write code that does little or no
 * direct pointer manipulation for copying and formatting data. For
 * example, the QCBOR encoder was written using these and has less
 * pointer manipulation.
 *
 * While it is true that object code using these functions will be a
 * little larger and slower than a white-knuckle clever use of
 * pointers might be, but not by that much or enough to have an effect
 * for most use cases. For security-oriented code this is highly
 * worthwhile. Clarity, simplicity, reviewability and are more
 * important.
 *
 * There are some extra sanity and double checks in this code to help
 * catch coding errors and simple memory corruption. They are helpful,
 * but not a substitute for proper code review, input validation and
 * such.
 *
 * This code consists of a lot of inline functions and a few that are
 * not.  It should not generate very much object code, especially with
 * the optimizer turned up to @c -Os or @c -O3.
 */


/**
 * @ref UsefulBufC and @ref UsefulBuf are simple data structures to
 * hold a pointer and length for binary data.  In C99 this data
 * structure can be passed on the stack making a lot of code cleaner
 * than carrying around a pointer and length as two parameters.
 *
 * This is also conducive to secure coding practice as the length is
 * always carried with the pointer and the convention for handling a
 * pointer and a length is clear.
 *
 * While it might be possible to write buffer and pointer code more
 * efficiently in some use cases, the thought is that unless there is
 * an extreme need for performance (e.g., you are building a
 * gigabit-per-second IP router), it is probably better to have
 * cleaner code you can be most certain about the security of.
 *
 * The non-const @ref UsefulBuf is usually used to refer an empty
 * buffer to be filled in.  The length is the size of the buffer.
 *
 * The const @ref UsefulBufC is usually used to refer to some data
 * that has been filled in. The length is amount of valid data pointed
 * to.
 *
 * A common use mode is to pass a @ref UsefulBuf to a function, the
 * function puts some data in it, then the function returns a @ref
 * UsefulBufC refering to the data. The @ref UsefulBuf is a non-const
 * "in" parameter and the @ref UsefulBufC is a const "out" parameter
 * so the constness stays correct. There is no single "in,out"
 * parameter (if there was, it would have to be non-const).  Note that
 * the pointer returned in the @ref UsefulBufC usually ends up being
 * the same pointer passed in as a @ref UsefulBuf, though this is not
 * striclty required.
 *
 * A @ref UsefulBuf is null, it has no value, when @c ptr in it is
 * @c NULL.
 *
 * There are functions and macros for the following:
 *  - Initializing
 *  - Create initialized const @ref UsefulBufC from compiler literals
 *  - Create initialized const @ref UsefulBufC from NULL-terminated string
 *  - Make an empty @ref UsefulBuf on the stack
 *  - Checking whether a @ref UsefulBuf is null, empty or both
 *  - Copying, copying with offset, copying head or tail
 *  - Comparing and finding substrings
 *
 * See also @ref UsefulOutBuf. It is a richer structure that has both
 * the size of the valid data and the size of the buffer.
 *
 * @ref UsefulBuf is only 16 or 8 bytes on a 64- or 32-bit machine so
 * it can go on the stack and be a function parameter or return value.
 *
 * Another way to look at it is this. C has the NULL-terminated string
 * as a means for handling text strings, but no means or convention
 * for binary strings. Other languages do have such means, Rust, an
 * efficient compiled language, for example.
 *
 * @ref UsefulBuf is kind of like the Useful Pot Pooh gave Eeyore on
 * his birthday.  Eeyore's balloon fits beautifully, "it goes in and
 * out like anything".
 */
typedef struct q_useful_buf_c {
    const void *ptr;
    size_t      len;
} UsefulBufC;


/**
 * This non-const @ref UsefulBuf is typically used for some allocated
 * memory that is to be filled in. The @c len is the amount of memory,
 * not the length of the valid data in the buffer.
 */
typedef struct q_useful_buf {
   void  *ptr;
   size_t len;
} UsefulBuf;


/**
 * A null @ref UsefulBufC is one that has no value in the same way a
 * @c NULL pointer has no value.  A @ref UsefulBufC is @c NULL when
 * the @c ptr field is @c NULL. It doesn't matter what @c len is.  See
 * UsefulBuf_IsEmpty() for the distinction between null and empty.
 */
/*
 * NULLUsefulBufC and few other macros have to be
 * definied differently in C than C++ because there
 * is no common construct for a literal structure.
 *
 * In C compound literals are used.
 *
 * In C++ list initalization is used. This only works
 * in C++11 and later.
 *
 * Note that some popular C++ compilers can handle compound
 * literals with on-by-default extensions, however
 * this code aims for full correctness with strict
 * compilers so they are not used.
 */
#ifdef __cplusplus
#define NULLUsefulBufC {NULL, 0}
#else
#define NULLUsefulBufC ((UsefulBufC) {NULL, 0})
#endif

/**
 * A null @ref UsefulBuf is one that has no memory associated the same
 * way @c NULL points to nothing. It does not matter what @c len is.
 **/
#ifdef __cplusplus
#define NULLUsefulBuf  {NULL, 0}
#else
#define NULLUsefulBuf  ((UsefulBuf) {NULL, 0})
#endif


/**
 * @brief Check if a @ref UsefulBuf is @ref NULLUsefulBuf or not.
 *
 * @param[in] UB The UsefulBuf to check.
 *
 * @return 1 if it is @ref NULLUsefulBuf, 0 if not.
 */
static inline int UsefulBuf_IsNULL(UsefulBuf UB);


/**
 * @brief Check if a @ref UsefulBufC is @ref NULLUsefulBufC or not.
 *
 * @param[in] UB The @ref UsefulBufC to check.
 *
 * @return 1 if it is @c NULLUsefulBufC, 0 if not.
 */
static inline int UsefulBuf_IsNULLC(UsefulBufC UB);


/**
 * @brief Check if a @ref UsefulBuf is empty or not.
 *
 * @param[in] UB The @ref UsefulBuf to check.
 *
 * @return 1 if it is empty, 0 if not.
 *
 * An "empty" @ref UsefulBuf is one that has a value and can be
 * considered to be set, but that value is of zero length.  It is
 * empty when @c len is zero. It doesn't matter what the @c ptr is.
 *
 * Many uses will not need to clearly distinguish a @c NULL @ref
 * UsefulBuf from an empty one and can have the @c ptr @c NULL and the
 * @c len 0.  However if a use of @ref UsefulBuf needs to make a
 * distinction then @c ptr should not be @c NULL when the @ref
 * UsefulBuf is considered empty, but not @c NULL.
 */
static inline int UsefulBuf_IsEmpty(UsefulBuf UB);


/**
 * @brief Check if a @ref UsefulBufC is empty or not.
 *
 * @param[in] UB The @ref UsefulBufC to check.
 *
 * @return 1 if it is empty, 0 if not.
 */
static inline int UsefulBuf_IsEmptyC(UsefulBufC UB);


/**
 * @brief Check if a @ref UsefulBuf is @ref NULLUsefulBuf or empty.
 *
 * @param[in] UB The @ref UsefulBuf to check.
 *
 * @return 1 if it is either @ref NULLUsefulBuf or empty, 0 if not.
 */
static inline int UsefulBuf_IsNULLOrEmpty(UsefulBuf UB);


/**
 * @brief Check if a @ref UsefulBufC is @ref NULLUsefulBufC or empty.
 *
 * @param[in] UB The @ref UsefulBufC to check.
 *
 * @return 1 if it is either @ref NULLUsefulBufC or empty, 0 if not.
 */
static inline int UsefulBuf_IsNULLOrEmptyC(UsefulBufC UB);


/**
 * @brief Convert a non-const @ref UsefulBuf to a const @ref UsefulBufC.
 *
 * @param[in] UB The @ref UsefulBuf to convert.
 *
 * @return A @ref UsefulBufC struct.
 */
static inline UsefulBufC UsefulBuf_Const(const UsefulBuf UB);


/**
 * @brief Convert a const @ref UsefulBufC to a non-const @ref UsefulBuf.
 *
 * @param[in] UBC The @ref UsefulBuf to convert.
 *
 * @return A non-const @ref UsefulBuf struct.
 *
 * Use of this is not necessary for the intended use mode of @ref
 * UsefulBufC and @ref UsefulBuf.  In that mode, the @ref UsefulBuf is
 * created to describe a buffer that has not had any data put in
 * it. Then the data is put in it.  Then a @ref UsefulBufC is create
 * to describe the part with the data in it. This goes from non-const
 * to const, so this function is not needed.
 *
 * If the -Wcast-qual warning is enabled, this function can be used to
 * avoid that warning.
 */
static inline UsefulBuf UsefulBuf_Unconst(const UsefulBufC UBC);


/**
 * Convert a literal string to a @ref UsefulBufC.
 *
 * @c szString must be a literal string that @c sizeof() works on.
 * This is better for literal strings than UsefulBuf_FromSZ() because
 * it generates less code. It will not work on non-literal strings.
 *
 * The terminating \0 (NULL) is NOT included in the length!
 */
#ifdef __cplusplus
#define UsefulBuf_FROM_SZ_LITERAL(szString)  {(szString), sizeof(szString)-1}
#else
#define UsefulBuf_FROM_SZ_LITERAL(szString) \
    ((UsefulBufC) {(szString), sizeof(szString)-1})
#endif


/**
 * Convert a literal byte array to a @ref UsefulBufC.
 *
 * @c pBytes must be a literal string that @c sizeof() works on.  It
 * will not work on non-literal arrays.
 */
#ifdef __cplusplus
#define UsefulBuf_FROM_BYTE_ARRAY_LITERAL(pBytes)  {(pBytes), sizeof(pBytes)}
#else
#define UsefulBuf_FROM_BYTE_ARRAY_LITERAL(pBytes) \
   ((UsefulBufC) {(pBytes), sizeof(pBytes)})
#endif

/**
 * Make an automatic variable named @c name of type @ref UsefulBuf and
 * point it to a stack variable of the given @c size.
 */
#define  UsefulBuf_MAKE_STACK_UB(name, size) \
    uint8_t    __pBuf##name[(size)];\
    UsefulBuf  name = {__pBuf##name , sizeof( __pBuf##name )}


/**
 * Make a byte array in to a @ref UsefulBuf. This is usually used on
 * stack variables or static variables.  Also see @ref
 * UsefulBuf_MAKE_STACK_UB.
 */
#ifdef __cplusplus
#define UsefulBuf_FROM_BYTE_ARRAY(pBytes)  {(pBytes), sizeof(pBytes)}
#else
#define UsefulBuf_FROM_BYTE_ARRAY(pBytes) \
   ((UsefulBuf) {(pBytes), sizeof(pBytes)})
#endif


/**
 * @brief Convert a NULL-terminated string to a @ref UsefulBufC.
 *
 * @param[in] szString The string to convert.
 *
 * @return A @ref UsefulBufC struct.
 *
 * @c UsefulBufC.ptr points to the string so its lifetime must be
 * maintained.
 *
 * The terminating \0 (NULL) is NOT included in the length.
 */
static inline UsefulBufC UsefulBuf_FromSZ(const char *szString);


/**
 * @brief Copy one @ref UsefulBuf into another at an offset.
 *
 * @param[in] Dest     Destination buffer to copy into.
 * @param[in] uOffset  The byte offset in @c Dest at which to copy to.
 * @param[in] Src      The bytes to copy.
 *
 * @return Pointer and length of the copy or @ref NULLUsefulBufC.
 *
 * This fails and returns @ref NULLUsefulBufC if @c offset is beyond the
 * size of @c Dest.
 *
 * This fails and returns @ref NULLUsefulBufC if the @c Src length
 * plus @c uOffset is greater than the length of @c Dest.
 *
 * The results are undefined if @c Dest and @c Src overlap.
 *
 * This assumes that there is valid data in @c Dest up to @c
 * uOffset. The @ref UsefulBufC returned starts at the beginning of @c
 * Dest and goes to @c Src.len @c + @c uOffset.
 */
UsefulBufC UsefulBuf_CopyOffset(UsefulBuf Dest, size_t uOffset, const UsefulBufC Src);


/**
 * @brief Copy one @ref UsefulBuf into another.
 *
 * @param[in] Dest  The destination buffer to copy into.
 * @param[out] Src  The source to copy from.
 *
 * @return Filled in @ref UsefulBufC on success, @ref NULLUsefulBufC
 *         on failure.
 *
 * This fails if @c Src.len is greater than @c Dest.len.
 *
 * Note that like @c memcpy(), the pointers are not checked and this
 * will crash rather than return @ref NULLUsefulBufC if they are @c
 * NULL or invalid.
 *
 * The results are undefined if @c Dest and @c Src overlap.
 */
static inline UsefulBufC UsefulBuf_Copy(UsefulBuf Dest, const UsefulBufC Src);


/**
 * @brief Set all bytes in a @ref UsefulBuf to a value, for example to 0.
 *
 * @param[in] pDest  The destination buffer to copy into.
 * @param[in] value  The value to set the bytes to.
 *
 * Note that like @c memset(), the pointer in @c pDest is not checked
 * and this will crash if @c NULL or invalid.
 */
static inline UsefulBufC UsefulBuf_Set(UsefulBuf pDest, uint8_t value);


/**
 * @brief Copy a pointer into a @ref UsefulBuf.
 *
 * @param[in,out] Dest  The destination buffer to copy into.
 * @param[in] ptr       The source to copy from.
 * @param[in] uLen      Length of the source; amount to copy.
 *
 * @return Filled in @ref UsefulBufC on success, @ref NULLUsefulBufC
 *         on failure.
 *
 * This fails and returns @ref NULLUsefulBufC if @c uLen is greater
 * than @c pDest->len.
 *
 * Note that like @c memcpy(), the pointers are not checked and this
 * will crash, rather than return 1 if they are @c NULL or invalid.
 */
static inline UsefulBufC UsefulBuf_CopyPtr(UsefulBuf Dest,
                                           const void *ptr,
                                           size_t uLen);


/**
 *  @brief Returns a truncation of a @ref UsefulBufC.
 *
 *  @param[in] UB       The buffer to get the head of.
 *  @param[in] uAmount  The number of bytes in the head.
 *
 *  @return A @ref UsefulBufC that is the head of UB.
 */
static inline UsefulBufC UsefulBuf_Head(UsefulBufC UB, size_t uAmount);


/**
 * @brief  Returns bytes from the end of a @ref UsefulBufC.
 *
 * @param[in] UB       The buffer to get the tail of.
 * @param[in] uAmount  The offset from the start where the tail is to begin.
 *
 * @return A @ref UsefulBufC that is the tail of @c UB or @ref NULLUsefulBufC
 *         if @c uAmount is greater than the length of the @ref UsefulBufC.
 *
 * If @c UB.ptr is @c NULL, but @c UB.len is not zero, then the result will
 * be a @ref UsefulBufC with a @c NULL @c ptr and @c len with the length
 * of the tail.
 */
static inline UsefulBufC UsefulBuf_Tail(UsefulBufC UB, size_t uAmount);


/**
 * @brief Compare one @ref UsefulBufC to another.
 *
 * @param[in] UB1  The first buffer to compare.
 * @param[in] UB2  The second buffer to compare.
 *
 * @return 0, positive or negative value.
 *
 * Returns a negative value if @c UB1 if is less than @c UB2. @c UB1 is
 * less than @c UB2 if it is shorter or the first byte that is not the
 * same is less.
 *
 * Returns 0 if the inputs are the same.
 *
 * Returns a positive value if @c UB2 is less than @c UB1.
 *
 * All that is of significance is that the result is positive, negative
 * or 0. (This doesn't return the difference between the first
 * non-matching byte like @c memcmp() ).
 */
int UsefulBuf_Compare(const UsefulBufC UB1, const UsefulBufC UB2);


/**
 * @brief Find first byte that is not a particular byte value.
 *
 * @param[in] UB     The destination buffer for byte comparison.
 * @param[in] uValue The byte value to compare to.
 *
 * @return  Offset of first byte that isn't @c uValue or
 *          @c SIZE_MAX if all bytes are @c uValue.
 *
 * Note that unlike most comparison functions, 0
 * does not indicate a successful comparison, so the
 * test for match is:
 *
 *      UsefulBuf_IsValue(...) == SIZE_MAX
 *
 * If @c UB is null or empty, there is no match
 * and 0 is returned.
 */
size_t UsefulBuf_IsValue(const UsefulBufC UB, uint8_t uValue);


/**
 * @brief Find one @ref UsefulBufC in another.
 *
 * @param[in] BytesToSearch  Buffer to search through.
 * @param[in] BytesToFind    Buffer with bytes to be found.
 *
 * @return Position of found bytes or @c SIZE_MAX if not found.
 */
size_t UsefulBuf_FindBytes(UsefulBufC BytesToSearch, UsefulBufC BytesToFind);


/**
 * @brief Convert a pointer to an offset with bounds checking.
 *
 * @param[in] UB  A UsefulBuf.
 * @param[in] p   Pointer to convert to offset.
 *
 * @return SIZE_MAX if @c p is out of range, the byte offset if not.
*/
static inline size_t UsefulBuf_PointerToOffset(UsefulBufC UB, const void *p);


/**
 * @brief Convert an offset to a pointer with bounds checking.
 *
 * @param[in] UB       A UsefulBuf.
 * @param[in] uOffset  Offset in @c pUInBuf.
 *
 * @return @c NULL if @c uOffset is out of range, a pointer into the buffer if not.
 */
static inline const void *UsefulBuf_OffsetToPointer(UsefulBufC UB, size_t uOffset);


#ifndef USEFULBUF_DISABLE_DEPRECATED
/** Deprecated macro; use @ref UsefulBuf_FROM_SZ_LITERAL instead */
#define SZLiteralToUsefulBufC(szString)  UsefulBuf_FROM_SZ_LITERAL(szString)

/** Deprecated macro; use UsefulBuf_MAKE_STACK_UB instead */
#define  MakeUsefulBufOnStack(name, size) \
    uint8_t    __pBuf##name[(size)];\
    UsefulBuf  name = {__pBuf##name , sizeof( __pBuf##name )}

/** Deprecated macro; use @ref UsefulBuf_FROM_BYTE_ARRAY_LITERAL instead */
#define ByteArrayLiteralToUsefulBufC(pBytes) \
   UsefulBuf_FROM_BYTE_ARRAY_LITERAL(pBytes)

/** Deprecated function; use UsefulBuf_Unconst() instead */
static inline UsefulBuf UsefulBufC_Unconst(const UsefulBufC UBC)
{
   UsefulBuf UB;

   /* See UsefulBuf_Unconst() implementation for comment */
   UB.ptr = (void *)(uintptr_t)UBC.ptr;

   UB.len = UBC.len;

   return UB;
}
#endif /* USEFULBUF_DISABLE_DEPRECATED */




#ifndef USEFULBUF_DISABLE_ALL_FLOAT
/**
 * @brief Copy a @c float to a @c uint32_t.
 *
 * @param[in] f  Float value to copy.
 *
 * @return  A @c uint32_t with the float bits.
 *
 * Convenience function to avoid type punning, compiler warnings and
 * such. The optimizer usually reduces this to a simple assignment.  This
 * is a crusty corner of C.
 */
static inline uint32_t UsefulBufUtil_CopyFloatToUint32(float f);


/**
 * @brief Copy a @c double to a @c uint64_t.
 *
 * @param[in] d  Double value to copy.
 *
 * @return  A @c uint64_t with the double bits.
 *
 * Convenience function to avoid type punning, compiler warnings and
 * such. The optimizer usually reduces this to a simple assignment.  This
 * is a crusty corner of C.
 */
static inline uint64_t UsefulBufUtil_CopyDoubleToUint64(double d);


/**
 * @brief Copy a @c uint32_t to a @c float.
 *
 * @param[in] u32  Integer value to copy.
 *
 * @return  The value as a @c float.
 *
 * Convenience function to avoid type punning, compiler warnings and
 * such. The optimizer usually reduces this to a simple assignment.  This
 * is a crusty corner of C.
 */
static inline float UsefulBufUtil_CopyUint32ToFloat(uint32_t u32);


/**
 * @brief Copy a @c uint64_t to a @c double.
 *
 * @param[in] u64  Integer value to copy.
 *
 * @return  The value as a @c double.
 *
 * Convenience function to avoid type punning, compiler warnings and
 * such. The optimizer usually reduces this to a simple assignment.  This
 * is a crusty corner of C.
 */
static inline double UsefulBufUtil_CopyUint64ToDouble(uint64_t u64);
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */




/**
 * UsefulOutBuf is a structure and functions (an object) for
 * serializing data into a buffer to encode for a network protocol or
 * write data to a file.
 *
 * The main idea is that all the pointer manipulation is performed by
 * @ref UsefulOutBuf functions so the caller doesn't have to do any
 * pointer manipulation.  The pointer manipulation is centralized.
 * This code has been reviewed and written carefully so it
 * spares the caller of much of this work and results in safer code
 * with less effort.
 *
 * The @ref UsefulOutBuf methods that add data to the output buffer
 * always check the length and will never write off the end of the
 * output buffer. If an attempt to add data that will not fit is made,
 * an internal error flag will be set and further attempts to add data
 * will not do anything.
 *
 * There is no way to ever write off the end of that buffer when
 * calling the @c UsefulOutBuf_AddXxx() and
 * @c UsefulOutBuf_InsertXxx() functions.
 *
 * The functions to add data do not report success of failure. The
 * caller only needs to check for an error in the final call, either
 * UsefulOutBuf_OutUBuf() or UsefulOutBuf_CopyOut() to get the
 * result. This makes the calling code cleaner.
 *
 * There is a utility function to get the error status anytime along
 * the way for a special circumstance. There are functions to see how
 * much room is left and see if some data will fit too, but their use
 * is generally unnecessary.
 *
 * The general call flow is:
 *
 *    - Initialize by calling @ref UsefulOutBuf_Init(). The output
 *      buffer given to it can be from the heap, stack or
 *      otherwise. @ref UsefulOutBuf_MakeOnStack is a convenience
 *      macro that makes a buffer on the stack and initializes it.
 *
 *    - Call methods like UsefulOutBuf_InsertString(),
 *      UsefulOutBuf_AppendUint32() and UsefulOutBuf_InsertUsefulBuf()
 *      to output data. The append calls add data to the end of the
 *      valid data. The insert calls take a position argument.
 *
 *    - Call UsefulOutBuf_OutUBuf() or UsefulOutBuf_CopyOut() to see
 *      there were no errors and to get the serialized output bytes.
 *
 * @ref UsefulOutBuf can be used in a mode to calculate the size of
 * what would be output without actually outputting anything.  This is
 * useful to calculate the size of a buffer that is to be allocated to
 * hold the output. See @ref SizeCalculateUsefulBuf.
 *
 * Methods like UsefulOutBuf_InsertUint64() always output in network
 * byte order (big endian).
 *
 * The possible errors are:
 *
 *  - The @ref UsefulOutBuf was not initialized or was corrupted.
 *
 *  - An attempt was made to add data that will not fit.
 *
 *  - An attempt was made to insert data at a position beyond the end of
 *    the buffer.
 *
 *  - An attempt was made to insert data at a position beyond the valid
 *    data in the buffer.
 *
 * Some inexpensive simple sanity checks are performed before every
 * data addition to guard against use of an uninitialized or corrupted
 * UsefulOutBuf.
 *
 * @ref UsefulOutBuf has been used to create a CBOR encoder. The CBOR
 * encoder has almost no pointer manipulation in it, is easier to
 * read, and easier to review.
 *
 * A @ref UsefulOutBuf is small and can go on the stack:
 *   - 32 bytes (27 bytes plus alignment padding) on a 64-bit CPU
 *   - 16 bytes (15 bytes plus alignment padding) on a 32-bit CPU
 */
typedef struct useful_out_buf {
   /* PRIVATE DATA STRUCTURE */
   UsefulBuf  UB;       /* Memory that is being output to */
   size_t     data_len; /* length of the valid data, the insertion point */
   uint16_t   magic;    /* Used to detect corruption and lack
                         * of initialization */
   uint8_t    err;
} UsefulOutBuf;


/**
 * This is a @ref UsefulBuf value that can be passed to
 * UsefulOutBuf_Init() to have it calculate the size of the output
 * buffer needed. Pass this for @c Storage, call all the append and
 * insert functions normally, then call UsefulOutBuf_OutUBuf(). The
 * returned @ref UsefulBufC has the size.
 *
 * As one can see, this is just a NULL pointer and very large size.
 * The NULL pointer tells UsefulOutputBuf to not copy any data.
 */
#ifdef __cplusplus
#define SizeCalculateUsefulBuf {NULL, SIZE_MAX}
#else
#define SizeCalculateUsefulBuf ((UsefulBuf) {NULL, SIZE_MAX})
#endif


/**
 * @brief Initialize and supply the output buffer.
 *
 * @param[out] pUOutBuf  The @ref UsefulOutBuf to initialize.
 * @param[in] Storage    Buffer to output into.
 *
 * This initializes the @ref UsefulOutBuf with storage, sets the
 * current position to the beginning of the buffer and clears the
 * error state.
 *
 * See @ref SizeCalculateUsefulBuf for instructions on how to
 * initialize a @ref UsefulOutBuf to calculate the size that would be
 * output without actually outputting.
 *
 * This must be called before the @ref UsefulOutBuf is used.
 */
void UsefulOutBuf_Init(UsefulOutBuf *pUOutBuf, UsefulBuf Storage);


/**
 * Convenience macro to make a @ref UsefulOutBuf on the stack and
 * initialize it with a stack buffer of the given size. The variable
 * will be named @c name.
 */
#define  UsefulOutBuf_MakeOnStack(name, size) \
   uint8_t       __pBuf##name[(size)];\
   UsefulOutBuf  name;\
   UsefulOutBuf_Init(&(name), (UsefulBuf){__pBuf##name, (size)});


/**
 * @brief Reset a @ref UsefulOutBuf for re use.
 *
 * @param[in] pUOutBuf Pointer to the @ref UsefulOutBuf
 *
 * This sets the amount of data in the output buffer to none and
 * clears the error state.
 *
 * The output buffer is still the same one and size as from the
 * UsefulOutBuf_Init() call.
 *
 * This doesn't zero the data, just resets to 0 bytes of valid data.
 */
static inline void UsefulOutBuf_Reset(UsefulOutBuf *pUOutBuf);


/**
 * @brief Returns position of end of data in the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 *
 * @return position of end of data.
 *
 * On a freshly initialized @ref UsefulOutBuf with no data added, this
 * will return 0. After 10 bytes have been added, it will return 10
 * and so on.
 *
 * Generally, there is no need to call this for most uses of @ref
 * UsefulOutBuf.
 */
static inline size_t UsefulOutBuf_GetEndPosition(UsefulOutBuf *pUOutBuf);


/**
 * @brief Returns whether any data has been added to the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 *
 * @return 1 if output position is at start, 0 if not.
 */
static inline int UsefulOutBuf_AtStart(UsefulOutBuf *pUOutBuf);


/**
 * @brief Inserts bytes into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] NewData   The bytes to insert.
 * @param[in] uPos      Index in output buffer at which to insert.
 *
 * @c NewData is the pointer and length for the bytes to be added to
 * the output buffer. There must be room in the output buffer for all
 * of @c NewData or an error will occur.
 *
 * The insertion point must be between 0 and the current valid
 * data. If not, an error will occur. Appending data to the output
 * buffer is achieved by inserting at the end of the valid data. This
 * can be retrieved by calling UsefulOutBuf_GetEndPosition().
 *
 * When insertion is performed, the bytes between the insertion point
 * and the end of data previously added to the output buffer are slid
 * to the right to make room for the new data.
 *
 * Overlapping buffers are OK. @c NewData can point to data in the
 * output buffer.
 *
 * NewData.len may be 0 in which case nothing will be inserted.
 *
 * If an error occurs, an error state is set in the @ref
 * UsefulOutBuf. No error is returned.  All subsequent attempts to add
 * data will do nothing.
 *
 * The intended use is that all additions are made without checking
 * for an error. The error will be taken into account when
 * UsefulOutBuf_OutUBuf() returns @c NullUsefulBufC.
 * UsefulOutBuf_GetError() can also be called to check for an error.
 */
void UsefulOutBuf_InsertUsefulBuf(UsefulOutBuf *pUOutBuf,
                                  UsefulBufC NewData,
                                  size_t uPos);


/**
 * @brief Insert a data buffer into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] pBytes    Pointer to the bytes to insert
 * @param[in] uLen      Length of the bytes to insert
 * @param[in] uPos      Index in output buffer at which to insert
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same with
 * the difference being a pointer and length is passed in rather than an
 * @ref UsefulBufC.
 */
static inline void UsefulOutBuf_InsertData(UsefulOutBuf *pUOutBuf,
                                           const void *pBytes,
                                           size_t uLen,
                                           size_t uPos);


/**
 * @brief Insert a NULL-terminated string into the UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] szString  NULL-terminated string to insert.
 * @param[in] uPos      Index in output buffer at which to insert.
 */
static inline void UsefulOutBuf_InsertString(UsefulOutBuf *pUOutBuf,
                                             const char *szString,
                                             size_t uPos);


/**
 * @brief Insert a byte into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the UsefulOutBuf.
 * @param[in] byte      Bytes to insert.
 * @param[in] uPos      Index in output buffer at which to insert.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same
 * with the difference being a single byte is to be inserted.
 */
static inline void UsefulOutBuf_InsertByte(UsefulOutBuf *pUOutBuf,
                                           uint8_t byte,
                                           size_t uPos);


/**
 * @brief Insert a 16-bit integer into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf    Pointer to the @ref UsefulOutBuf.
 * @param[in] uInteger16  Integer to insert.
 * @param[in] uPos        Index in output buffer at which to insert.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same
 * with the difference being a two-byte integer is to be inserted.
 *
 * The integer will be inserted in network byte order (big endian).
 */
static inline void UsefulOutBuf_InsertUint16(UsefulOutBuf *pUOutBuf,
                                             uint16_t uInteger16,
                                             size_t uPos);


/**
 * @brief Insert a 32-bit integer into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf    Pointer to the @ref UsefulOutBuf.
 * @param[in] uInteger32  Integer to insert.
 * @param[in] uPos        Index in output buffer at which to insert.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same
 * with the difference being a four-byte integer is to be inserted.
 *
 * The integer will be inserted in network byte order (big endian).
 */
static inline void UsefulOutBuf_InsertUint32(UsefulOutBuf *pUOutBuf,
                                             uint32_t uInteger32,
                                             size_t uPos);


/**
 * @brief Insert a 64-bit integer into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf    Pointer to the @ref UsefulOutBuf.
 * @param[in] uInteger64  Integer to insert.
 * @param[in] uPos        Index in output buffer at which to insert.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same
 * with the difference being an eight-byte integer is to be inserted.
 *
 * The integer will be inserted in network byte order (big endian).
 */
static inline void UsefulOutBuf_InsertUint64(UsefulOutBuf *pUOutBuf,
                                             uint64_t uInteger64,
                                             size_t uPos);


#ifndef USEFULBUF_DISABLE_ALL_FLOAT
/**
 * @brief Insert a @c float into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] f         @c float to insert.
 * @param[in] uPos      Index in output buffer at which to insert.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same
 * with the difference being a @c float is to be inserted.
 *
 * The @c float will be inserted in network byte order (big endian).
 */
static inline void UsefulOutBuf_InsertFloat(UsefulOutBuf *pUOutBuf,
                                            float f,
                                            size_t uPos);


/**
 * @brief Insert a @c double into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] d         @c double  to insert.
 * @param[in] uPos      Index in output buffer at which to insert.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This is the same
 * with the difference being a @c double is to be inserted.
 *
 * The @c double will be inserted in network byte order (big endian).
 */
static inline void UsefulOutBuf_InsertDouble(UsefulOutBuf *pUOutBuf,
                                             double d,
                                             size_t uPos);
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */


/**
 * @brief Append a @ref UsefulBuf into the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] NewData   The @ref UsefulBuf with the bytes to append.
 *
 * See UsefulOutBuf_InsertUsefulBuf() for details. This does the same
 * with the insertion point at the end of the valid data.
 */
static inline void UsefulOutBuf_AppendUsefulBuf(UsefulOutBuf *pUOutBuf,
                                                UsefulBufC NewData);


/**
 * @brief Append bytes to the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] pBytes    Pointer to bytes to append.
 * @param[in] uLen      Length of @c pBytes to append.
 *
 * See UsefulOutBuf_InsertData() for details. This does the same with
 * the insertion point at the end of the valid data.
 */
static inline void UsefulOutBuf_AppendData(UsefulOutBuf *pUOutBuf,
                                           const void *pBytes,
                                           size_t uLen);


/**
 * @brief Append a NULL-terminated string to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] szString  NULL-terminated string to append.
 */
static inline void UsefulOutBuf_AppendString(UsefulOutBuf *pUOutBuf,
                                             const char *szString);


/**
 * @brief Append a byte to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] byte      Bytes to append.
 *
 * See UsefulOutBuf_InsertByte() for details. This does the same
 * with the insertion point at the end of the valid data.
 */
static inline void UsefulOutBuf_AppendByte(UsefulOutBuf *pUOutBuf,
                                           uint8_t byte);


/**
 * @brief Append an integer to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf    Pointer to the @ref UsefulOutBuf.
 * @param[in] uInteger16  Integer to append.
 *
 * See UsefulOutBuf_InsertUint16() for details. This does the same
 * with the insertion point at the end of the valid data.
 *
 * The integer will be appended in network byte order (big endian).
 */
static inline void UsefulOutBuf_AppendUint16(UsefulOutBuf *pUOutBuf,
                                             uint16_t uInteger16);


/**
 * @brief Append an integer to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf    Pointer to the @ref UsefulOutBuf.
 * @param[in] uInteger32  Integer to append.
 *
 * See UsefulOutBuf_InsertUint32() for details. This does the same
 * with the insertion point at the end of the valid data.
 *
 * The integer will be appended in network byte order (big endian).
 */
static inline void UsefulOutBuf_AppendUint32(UsefulOutBuf *pUOutBuf,
                                             uint32_t uInteger32);


/**
 * @brief Append an integer to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf    Pointer to the @ref UsefulOutBuf.
 * @param[in] uInteger64  Integer to append.
 *
 * See UsefulOutBuf_InsertUint64() for details. This does the same
 * with the insertion point at the end of the valid data.
 *
 * The integer will be appended in network byte order (big endian).
 */
static inline void UsefulOutBuf_AppendUint64(UsefulOutBuf *pUOutBuf,
                                             uint64_t uInteger64);


#ifndef USEFULBUF_DISABLE_ALL_FLOAT
/**
 * @brief Append a @c float to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] f         @c float to append.
 *
 * See UsefulOutBuf_InsertFloat() for details. This does the same with
 * the insertion point at the end of the valid data.
 *
 * The float will be appended in network byte order (big endian).
 */
static inline void UsefulOutBuf_AppendFloat(UsefulOutBuf *pUOutBuf,
                                            float f);


/**
 * @brief Append a @c double to the @ref UsefulOutBuf
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] d         @c double to append.
 *
 * See UsefulOutBuf_InsertDouble() for details. This does the same
 * with the insertion point at the end of the valid data.
 *
 * The double will be appended in network byte order (big endian).
 */
static inline void UsefulOutBuf_AppendDouble(UsefulOutBuf *pUOutBuf,
                                             double d);
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */


/**
 * @brief Returns the current error status.
 *
 * @param[in] pUOutBuf Pointer to the @ref UsefulOutBuf.
 *
 * @return 0 if all OK, 1 on error.
 *
 * This returns the error status since a call to either
 * UsefulOutBuf_Reset() of UsefulOutBuf_Init().  Once a @ref UsefulOutBuf
 * goes into the error state, it will stay until one of those
 * functions is called.
 *
 * Possible error conditions are:
 *   - bytes to be inserted will not fit
 *   - insertion point is out of buffer or past valid data
 *   - current position is off end of buffer (probably corrupted or uninitialized)
 *   - detect corruption / uninitialized by bad magic number
 */
static inline int UsefulOutBuf_GetError(UsefulOutBuf *pUOutBuf);


/**
 * @brief Returns number of bytes unused used in the output buffer.
 *
 * @param[in] pUOutBuf Pointer to the @ref UsefulOutBuf.
 *
 * @return Number of unused bytes or zero.
 *
 * Because of the error handling strategy and checks in
 * UsefulOutBuf_InsertUsefulBuf() it is usually not necessary to use
 * this.
 */
static inline size_t UsefulOutBuf_RoomLeft(UsefulOutBuf *pUOutBuf);


/**
 *@brief Returns 1 if some number of bytes will fit in the @ref UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf
 * @param[in] uLen      Number of bytes for which to check
 *
 * @return 1 if @c uLen bytes will fit, 0 if not.
 *
 * Because of the error handling strategy and checks in
 * UsefulOutBuf_InsertUsefulBuf() it is usually not necessary to use
 * this.
 */
static inline int UsefulOutBuf_WillItFit(UsefulOutBuf *pUOutBuf, size_t uLen);


 /**
  * @brief Returns 1 if buffer given to UsefulOutBuf_Init() was @c NULL.
  *
  * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf
  *
  * @return 1 if buffer given to UsefulOutBuf_Init() was @c NULL.
  *
  * Giving a @c NULL output buffer to UsefulOutBuf_Init() is used when
  * just calculating the length of the encoded data.
  */
static inline int UsefulOutBuf_IsBufferNULL(UsefulOutBuf *pUOutBuf);


/**
 * @brief Returns pointer and length of the output buffer not yet used.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 *
 * @return pointer and length of output buffer not used.
 *
 * This is an escape that allows the caller to write directly
 * to the output buffer without any checks. This doesn't
 * change the output buffer or state. It just returns a pointer
 * and length of the bytes remaining.
 *
 * This is useful to avoid having the bytes to be added all
 * in a contiguous buffer. Its use can save memory. A good
 * example is in the COSE encrypt implementation where
 * the output of the symmetric cipher can go directly
 * into the output buffer, rather than having to go into
 * an intermediate buffer.
 *
 * See UsefulOutBuf_Advance() which is used to tell
 * UsefulOutBuf how much was written.
 *
 * Warning: this bypasses the buffer safety provided by
 * UsefulOutBuf!
 */
static inline UsefulBuf
UsefulOutBuf_GetOutPlace(UsefulOutBuf *pUOutBuf);


/**
 * @brief Advance the amount output assuming it was written by the caller.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] uAmount  The amount to advance.
 *
 * This advances the position in the output buffer
 * by \c uAmount. This assumes that the
 * caller has written \c uAmount to the pointer obtained
 * with UsefulOutBuf_GetOutPlace().
 *
 * Warning: this bypasses the buffer safety provided by
 * UsefulOutBuf!
 */
void
UsefulOutBuf_Advance(UsefulOutBuf *pUOutBuf, size_t uAmount);


/**
 *  @brief Returns the data put into a UsefulOutBuf.
 *
 *  @param[in] pUOutBuf Pointer to the @ref UsefulOutBuf.
 *
 *  @return The valid data in @ref UsefulOutBuf or
 *           @ref NULLUsefulBufC if there was an error adding data.
 *
 *  The storage for the returned data is the @c Storage parameter
 *  passed to UsefulOutBuf_Init(). See also UsefulOutBuf_CopyOut().
 *
 *  This can be called anytime and many times to get intermediate
 *  results. It doesn't change the data or reset the current position,
 *  so further data can be added.
 */
UsefulBufC UsefulOutBuf_OutUBuf(UsefulOutBuf *pUOutBuf);


/**
 * @brief Copy out the data put into a UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[out] Dest     The destination buffer to copy into.
 *
 * @return Pointer and length of copied data or @c NULLUsefulBufC
 *         if it will not fit in the @c Dest buffer or the error
 *         state was entered.
 *
 * This is the same as UsefulOutBuf_OutUBuf() except it copies the
 * data to @c Dest rather than returning a pointer.
 */
UsefulBufC UsefulOutBuf_CopyOut(UsefulOutBuf *pUOutBuf, UsefulBuf Dest);


/**
 * @brief Returns data starting at an offset that was put into a UsefulOutBuf.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] uOffset    Offset to bytes to return.
 *
 * @return NULLUsefulBufC or the bytes at the offset.
 *
 * This is the same as UsefulOutBuf_OutUBuf() except a starting offset
 * maybe specified. It returns the bytes starting at @c uOffset to the
 * end of what was encoded so far. Calling this with @c uOffset 0 is
 * equivalent to UsefulOutBuf_OutUBuf().
 *
 * If there's nothing at @c uOffset or it is past the in the output
 * buffer, a \ref NULLUsefulBufC is returned.
 *
 * This is typically not needed in typical use. It is used by QCBOR
 * along with UsefulOutBuf_Compare() and UsefulOutBuf_Swap() for
 * sorting CBOR maps.
 */
UsefulBufC
UsefulOutBuf_OutUBufOffset(UsefulOutBuf *pUOutBuf, size_t uOffset);


/*
 * @brief Return a substring of the output data.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] uStart    Offset of start of substring.
 * @param[in] uLen      Length of substring.
 *
 * This is the same as UsefulOutBuf_OutUBuf(), but returns a
 * substring. @c NULLUsefulBufC is returned if the requested substring
 * is off the end of the output bytes or if in error state.
 */
UsefulBufC UsefulOutBuf_SubString(UsefulOutBuf *pUOutBuf,
                                  const size_t  uStart,
                                  const size_t  uLen);


/**
 * @brief Retrieve the storage buffer passed in to UsefulOutBuf_Init().
 *
 * @param[in] pUOutBuf  The encoding context.
 *
 * @return The output storage buffer passed to UsefulOutBuf_Init().
 *
 * This doesn't give any information about how much has been encoded
 * or the error state. It just returns the exact @ref UsefulOutBuf given
 * to UsefulOutBuf_Init().
 */
static UsefulBuf UsefulOutBuf_RetrieveOutputStorage(UsefulOutBuf *pUOutBuf);


/**
 * @brief Compare bytes at offsets.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] uStart1   Offset of first bytes to compare.
 * @param[in] uLen1     Length of first bytes to compare.
 * @param[in] uStart2   Offset of second bytes to compare.
 * @param[in] uLen2     Length of second bytes to compare.
 *
 * @return  0 for equality, positive if uStart1 is lexographically larger,
 *          negative if uStart2 is lexographically larger.
 * 
 * This looks into bytes that have been output at the offsets @c start1
 * and @c start2. It compares bytes at those two starting points until
 * they are not equal or @c uLen1 or @c uLen2 is reached. If the
 * length of the string given is off the end of the output data, the
 * string will be effectively truncated to the data in the output
 * buffer for the comparison.
 *
 * This returns positive when @c uStart1 lexographically sorts ahead
 * of @c uStart2 and vice versa.  Zero is returned if the strings
 * compare equally.
 *
 * If lengths are unequal and the first bytes are an exact subset of
 * the second string, then a positve value will be returned and vice
 * versa.
 *
 * If either start is past the end of data in the output buffer, 0
 * will be returned. It is the caller's responsibility to make sure
 * the offsets are not off the end so that a comparison is actually
 * being made. No data will ever be read off the end of the buffer so
 * this safe no matter what offsets are passed.
 *
 * This is a relatively odd function in that it works on data in the
 * output buffer. It is employed by QCBOR to sort CBOR-encoded maps
 * that are in the output buffer.
 */
int UsefulOutBuf_Compare(UsefulOutBuf *pUOutBuf,
                         size_t uStart1, size_t uLen1,
                         size_t uStart2, size_t uLen2);

/**
 * @brief Swap two regions of output bytes.
 *
 * @param[in] pUOutBuf  Pointer to the @ref UsefulOutBuf.
 * @param[in] uStartOffset   Offset to start of bytes to be swapped.
 * @param[in] uPivotOffset   Offset to pivot around which bytes are swapped.
 * @param[in] uEndOffset       Offset to end of region to be swappe.
 *
 * This reaches into bytes that have been output and swaps two
 * adjacent regions.
 *
 * If any of the offsets are outside the range of valid data, no
 * swapping will be performed. If the start is not the smallest and
 * the pivot is not in the middle no swapping will be performed.
 *
 * The byte at @c uStartOffset will participate in the swapping.  The
 * byte at @c uEndOffset will not participate in the swapping, only
 * the byte before it.
 *
 * This is a relatively odd function in that it works on data in the
 * output buffer. It is employed by QCBOR to bubble sort encoded CBOR
 * maps.
 */
void UsefulOutBuf_Swap(UsefulOutBuf *pUOutBuf,
                       size_t        uStartOffset,
                       size_t        uPivotOffset,
                       size_t        uEndOffset);




/**
 * @ref UsefulInputBuf is the counterpart to @ref UsefulOutBuf. It is
 * for parsing data received.  Initialize it with the data from the
 * network. Then use the functions like UsefulInputBuf_GetBytes() to
 * get data chunks of various types. A position cursor is maintained
 * internally.
 *
 * As long as the functions here are used, there will never be any
 * reference off the end of the given buffer (except
 * UsefulInputBuf_SetBufferLength()). This is true even if they are
 * called incorrectly, an attempt is made to seek off the end of the
 * buffer or such. This makes it easier to write safe and correct
 * code.  For example, the QCBOR decoder implementation is safer and
 * easier to review through its use of @ref UsefulInputBuf.
 *
 * @ref UsefulInputBuf maintains an internal error state.  The
 * intended use is fetching data chunks without any error checks until
 * the end.  If there was any error, such as an attempt to fetch data
 * off the end, the error state is entered and no further data will be
 * returned. In the error state the @c UsefulInputBuf_GetXxxx()
 * functions return 0, or @c NULL or @ref NULLUsefulBufC. As long as
 * null is not dereferenced, the error check can be put off until the
 * end, simplifying the calling code.
 *
 * The integer and float parsing expects network byte order (big
 * endian).  Network byte order is what is used by TCP/IP, CBOR and
 * most internet protocols.
 *
 * Lots of inline functions are used to keep code size down. The
 * optimizer, particularly with the @c -Os or @c -O3, also reduces
 * code size a lot. The only non-inline code is
 * UsefulInputBuf_GetBytes().  It is less than 100 bytes so use of
 * @ref UsefulInputBuf doesn't add much code for all the messy
 * hard-to-get right issues with parsing binary protocols in C that it
 * solves.
 *
 * The parse context size is:
 *   - 64-bit machine: 16 + 8 + 2 + 1 (+ 5 bytes padding to align) = 32 bytes
 *   - 32-bit machine: 8 + 4 + 2 + 1 (+ 1 byte padding to align) = 16 bytes
 */
typedef struct useful_input_buf {
   /* PRIVATE DATA STRUCTURE */
   UsefulBufC UB;     /* Data being parsed */
   size_t     cursor; /* Current offset in data being parse */
   uint16_t   magic;  /* Check for corrupted or uninitialized UsefulInputBuf */
   uint8_t    err;    /* Set request goes off end or magic number is bad */
} UsefulInputBuf;

#define UIB_MAGIC (0xB00F)


/**
 * @brief Initialize the @ref UsefulInputBuf structure before use.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] UB       The data to parse.
 */
static inline void UsefulInputBuf_Init(UsefulInputBuf *pUInBuf, UsefulBufC UB);


/**
 * @brief Returns current position in input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return Integer position of the cursor.
 *
 * The position that the next bytes will be returned from.
 */
static size_t UsefulInputBuf_Tell(UsefulInputBuf *pUInBuf);


/**
 * @brief Sets the current position in input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] uPos     Position to set to.
 *
 * If the position is off the end of the input buffer, the error state
 * is entered.
 *
 * Seeking to a valid position in the buffer will not reset the error
 * state. Only re-initialization will do that.
 */
static void UsefulInputBuf_Seek(UsefulInputBuf *pUInBuf, size_t uPos);


/**
 * @brief Returns the number of bytes from the cursor to the end of the buffer,
 * the unconsumed bytes.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return Number of bytes unconsumed or 0 on error.
 *
 * Returns 0 if the cursor is invalid or corruption of the
 * @ref UsefulInputBuf structure is detected.
 */
static size_t UsefulInputBuf_BytesUnconsumed(UsefulInputBuf *pUInBuf);


/**
 * @brief Check if there are unconsumed bytes.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] uLen     Number of bytes to check availability for.
 *
 * @return 1 if @c uLen bytes are available after the cursor, and 0 if not.
 */
static int UsefulInputBuf_BytesAvailable(UsefulInputBuf *pUInBuf, size_t uLen);


/**
 * @brief Convert a pointer to an offset with bounds checking.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] p        Pointer to convert to offset.
 *
 * @return SIZE_MAX if @c p is out of range, the byte offset if not.
 */
static size_t UsefulInputBuf_PointerToOffset(UsefulInputBuf *pUInBuf, const void *p);


/**
 * @brief Convert an offset to a pointer with bounds checking.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] uOffset  Offset in @c pUInBuf.
 *
 * @return @c NULL if @c uOffset is out of range, a pointer into the buffer if not.
 */
static const void *UsefulInputBuf_OffsetToPointer(UsefulInputBuf *pUInBuf, size_t uOffset);


/**
 * @brief Get pointer to bytes out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] uNum     Number of bytes to get.
 *
 * @return Pointer to bytes.
 *
 * This consumes @c uNum bytes from the input buffer. This returns a
 * pointer to the start of the @c uNum bytes.
 *
 * If there are not @c uNum bytes in the input buffer, @c NULL will be
 * returned and the error state is entered.
 *
 * This advances the position cursor by @c uNum bytes.
 */
const void * UsefulInputBuf_GetBytes(UsefulInputBuf *pUInBuf, size_t uNum);


/**
 * @brief Get @ref UsefulBuf out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] uNum     Number of bytes to get.
 *
 * @return A @ref UsefulBufC with ptr and length of bytes consumed.
 *
 * This consumes @c uNum bytes from the input buffer and returns the
 * pointer and length for them as a @ref UsefulBufC. The length
 * returned will always be @c uNum. The position cursor is advanced by
 * @c uNum bytes.
 *
 * If there are not @c uNum bytes in the input buffer, @ref
 * NULLUsefulBufC will be returned and the error state is entered.
 */
static inline UsefulBufC UsefulInputBuf_GetUsefulBuf(UsefulInputBuf *pUInBuf, size_t uNum);


/**
 * @brief Get a byte out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The byte.
 *
 * This consumes 1 byte from the input buffer, returns it and advances
 * the position cursor by 1.
 *
 * If there is not 1 byte in the buffer, 0 will be returned for the
 * byte and the error state is entered. To know if the 0 returned was
 * in error or the real value, the error state must be checked.  If
 * possible, put this off until all values are retrieved to have
 * smaller and simpler code, but if not possible
 * UsefulInputBuf_GetError() can be called. Also, in the error state
 * UsefulInputBuf_GetBytes() returns @c NULL *or the @c ptr from
 * UsefulInputBuf_GetUsefulBuf() is @c NULL.
 */
static inline uint8_t UsefulInputBuf_GetByte(UsefulInputBuf *pUInBuf);


/**
 * @brief Get a @c uint16_t out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The @c uint16_t.
 *
 * See UsefulInputBuf_GetByte(). This works the same, except it returns
 * a @c uint16_t and two bytes are consumed.
 *
 * The input bytes are interpreted in network order (big endian).
 */
static inline uint16_t UsefulInputBuf_GetUint16(UsefulInputBuf *pUInBuf);


/**
 * @brief Get a @c uint32_t out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The @c uint32_t.
 *
 * See UsefulInputBuf_GetByte(). This works the same, except it
 * returns a @c uint32_t and four bytes are consumed.
 *
 * The input bytes are interpreted in network order (big endian).
 */
static uint32_t UsefulInputBuf_GetUint32(UsefulInputBuf *pUInBuf);


/**
 * @brief Get a @c uint64_t out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The uint64_t.
 *
 * See UsefulInputBuf_GetByte(). This works the same, except it returns
 * a @c uint64_t and eight bytes are consumed.
 *
 * The input bytes are interpreted in network order (big endian).
 */
static uint64_t UsefulInputBuf_GetUint64(UsefulInputBuf *pUInBuf);


#ifndef USEFULBUF_DISABLE_ALL_FLOAT
/**
 * @brief Get a float out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The float.
 *
 * See UsefulInputBuf_GetByte(). This works the same, except it
 * returns a float and four bytes are consumed.
 *
 * The input bytes are interpreted in network order (big endian).
 */
static float UsefulInputBuf_GetFloat(UsefulInputBuf *pUInBuf);


/**
 * @brief Get a double out of the input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The double.
 *
 * See UsefulInputBuf_GetByte(). This works the same, except it
 * returns a double and eight bytes are consumed.
 *
 * The input bytes are interpreted in network order (big endian).
 */
static double UsefulInputBuf_GetDouble(UsefulInputBuf *pUInBuf);
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */


/**
 * @brief Get the error status.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return 0 if not in the error state, 1 if in the error state.
 *
 * This returns whether the @ref UsefulInputBuf is in the
 * error state or not.
 *
 * The error state is entered for one of these reasons:
 * - Attempt to fetch data past the end of the buffer
 * - Attempt to seek to a position past the end of the buffer
 * - Attempt to get data from an uninitialized  or corrupt instance
 *   of @ref UsefulInputBuf
 *
 * Once in the error state, it can only be cleared by calling
 * UsefulInputBuf_Init().
 *
 * For many use cases, it is possible to only call this once after all
 * the @c UsefulInputBuf_GetXxxx() calls have been made.  This is
 * possible if no reference to the data returned are needed before the
 * error state is checked.
 *
 * In some cases UsefulInputBuf_GetUsefulBuf() or
 * UsefulInputBuf_GetBytes() can stand in for this because they return
 * @c NULL if the error state has been entered. (The others can't stand
 * in because they don't return a clearly distinct error value.)
 */
static int UsefulInputBuf_GetError(UsefulInputBuf *pUInBuf);


/**
 * @brief Gets the input buffer length.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The length of the input buffer.
 *
 * This returns the length of the input buffer set by
 * UsefulInputBuf_Init() or UsefulInputBuf_SetBufferLength().
 */
static inline size_t UsefulInputBuf_GetBufferLength(UsefulInputBuf *pUInBuf);


/**
 * @brief Alters the input buffer length (use with caution).
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 * @param[in] uNewLen  The new length of the input buffer.
 *
 * This alters the internal remembered length of the input buffer set
 * when UsefulInputBuf_Init() was called.
 *
 * The new length given here should always be equal to or less than
 * the length given when UsefulInputBuf_Init() was called. Making it
 * larger allows @ref UsefulInputBuf to run off the input buffer.
 *
 * The typical use is to set a length shorter than that when
 * initialized to constrain parsing. If
 * UsefulInputBuf_GetBufferLength() was called before this, then the
 * original length can be restored with another call to this.
 *
 * This should be used with caution. It is the only
 * @ref UsefulInputBuf method that can violate the safety of input
 * buffer parsing.
 */
static void UsefulInputBuf_SetBufferLength(UsefulInputBuf *pUInBuf, size_t uNewLen);


/** @brief  Retrieve the undecoded input buffer.
 *
 * @param[in] pUInBuf  Pointer to the @ref UsefulInputBuf.
 *
 * @return The input that was given to UsefulInputBuf_Init().
 *
 * A simple convenience method, should it be useful to get the original input back.
 */
static UsefulBufC UsefulInputBuf_RetrieveUndecodedInput(UsefulInputBuf *pUInBuf);


/**
 * @brief Compare two ranges of bytes somewhere in the input buffer.
 *
 * @param[in] pUInBuf   The input buffer.
 * @param[in] uOffset1  Offset of first range of bytes.
 * @param[in] uLen1     Length of first range of bytes.
 * @param[in] uOffset2  Offset of second range of bytes.
 * @param[in] uLen2     Length of second range of bytes.
 *
 * This returns the same as UsefulBuf_Compare().
 * 
 * If the offset or the length plus offset or a range extends outside
 * the input buffer, that range of bytes will be considered greater
 * than the other string. If both are outside this is considered a
 * degenerate condition and the first string is considered larger.
 *
 * This is a somewhat odd function of UsefulInputBuf as it is not used
 * for consuming data. QCBOR uses it for map order and duplicate
 * checking.
 */
int
UsefulInputBuf_Compare(UsefulInputBuf *pUInBuf,
                       const size_t    uOffset1,
                       const size_t    uLen1,
                       const size_t    uOffset2,
                       const size_t    uLen2);




/*----------------------------------------------------------
 Inline implementations.
 */
static inline int UsefulBuf_IsNULL(UsefulBuf UB)
{
   return !UB.ptr;
}


static inline int UsefulBuf_IsNULLC(UsefulBufC UB)
{
   return !UB.ptr;
}


static inline int UsefulBuf_IsEmpty(UsefulBuf UB)
{
   return !UB.len;
}


static inline int UsefulBuf_IsEmptyC(UsefulBufC UB)
{
   return !UB.len;
}


static inline int UsefulBuf_IsNULLOrEmpty(UsefulBuf UB)
{
   return UsefulBuf_IsEmpty(UB) || UsefulBuf_IsNULL(UB);
}


static inline int UsefulBuf_IsNULLOrEmptyC(UsefulBufC UB)
{
   return UsefulBuf_IsEmptyC(UB) || UsefulBuf_IsNULLC(UB);
}


static inline UsefulBufC UsefulBuf_Const(const UsefulBuf UB)
{
   UsefulBufC UBC;
   UBC.ptr = UB.ptr;
   UBC.len = UB.len;

   return UBC;
}

static inline UsefulBuf UsefulBuf_Unconst(const UsefulBufC UBC)
{
   UsefulBuf UB;

   /* -Wcast-qual is a good warning flag to use in general. This is
    * the one place in UsefulBuf where it needs to be quieted.
    */
   UB.ptr = (void *)(uintptr_t)UBC.ptr;

   UB.len = UBC.len;

   return UB;
}


static inline UsefulBufC UsefulBuf_FromSZ(const char *szString)
{
   UsefulBufC UBC;
   UBC.ptr = szString;
   UBC.len = strlen(szString);
   return UBC;
}


static inline UsefulBufC UsefulBuf_Copy(UsefulBuf Dest, const UsefulBufC Src)
{
   return UsefulBuf_CopyOffset(Dest, 0, Src);
}


static inline UsefulBufC UsefulBuf_Set(UsefulBuf Dest, uint8_t value)
{
   memset(Dest.ptr, value, Dest.len);

   UsefulBufC UBC;
   UBC.ptr = Dest.ptr;
   UBC.len = Dest.len;

   return UBC;
}


static inline UsefulBufC UsefulBuf_CopyPtr(UsefulBuf Dest, const void *ptr, size_t len)
{
   UsefulBufC UBC;
   UBC.ptr = ptr;
   UBC.len = len;
   return UsefulBuf_Copy(Dest, UBC);
}


static inline UsefulBufC UsefulBuf_Head(UsefulBufC UB, size_t uAmount)
{
   if(uAmount > UB.len) {
      return NULLUsefulBufC;
   }
   UsefulBufC UBC;

   UBC.ptr = UB.ptr;
   UBC.len = uAmount;

   return UBC;
}


static inline UsefulBufC UsefulBuf_Tail(UsefulBufC UB, size_t uAmount)
{
   UsefulBufC ReturnValue;

   if(uAmount > UB.len) {
      ReturnValue = NULLUsefulBufC;
   } else if(UB.ptr == NULL) {
      ReturnValue.ptr = NULL;
      ReturnValue.len = UB.len - uAmount;
   } else {
      ReturnValue.ptr = (const uint8_t *)UB.ptr + uAmount;
      ReturnValue.len = UB.len - uAmount;
   }

   return ReturnValue;
}


static inline size_t UsefulBuf_PointerToOffset(UsefulBufC UB, const void *p)
{
   if(UB.ptr == NULL) {
      return SIZE_MAX;
   }

   if(p < UB.ptr) {
      /* given pointer is before start of buffer */
      return SIZE_MAX;
   }

   /* Cast to size_t (from ptrdiff_t) is OK because of check above */
   const size_t uOffset = (size_t)((const uint8_t *)p - (const uint8_t *)UB.ptr);

    if(uOffset >= UB.len) {
      /* given pointer is off the end of the buffer */
      return SIZE_MAX;
   }

   return uOffset;
}


static inline const void *UsefulBuf_OffsetToPointer(UsefulBufC UB, size_t uOffset)
{
   if(UsefulBuf_IsNULLC(UB) || uOffset >= UB.len) {
      return NULL;
   }

   return (const uint8_t *)UB.ptr + uOffset;
}




#ifndef USEFULBUF_DISABLE_ALL_FLOAT
static inline uint32_t UsefulBufUtil_CopyFloatToUint32(float f)
{
   uint32_t u32;
   memcpy(&u32, &f, sizeof(uint32_t));
   return u32;
}

static inline uint64_t UsefulBufUtil_CopyDoubleToUint64(double d)
{
   uint64_t u64;
   memcpy(&u64, &d, sizeof(uint64_t));
   return u64;
}

static inline double UsefulBufUtil_CopyUint64ToDouble(uint64_t u64)
{
   double d;
   memcpy(&d, &u64, sizeof(uint64_t));
   return d;
}

static inline float UsefulBufUtil_CopyUint32ToFloat(uint32_t u32)
{
   float f;
   memcpy(&f, &u32, sizeof(uint32_t));
   return f;
}
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */




static inline void UsefulOutBuf_Reset(UsefulOutBuf *pMe)
{
   pMe->data_len = 0;
   pMe->err      = 0;
}


static inline size_t UsefulOutBuf_GetEndPosition(UsefulOutBuf *pMe)
{
   return pMe->data_len;
}


static inline int UsefulOutBuf_AtStart(UsefulOutBuf *pMe)
{
   return 0 == pMe->data_len;
}


static inline void UsefulOutBuf_InsertData(UsefulOutBuf *pMe,
                                           const void *pBytes,
                                           size_t uLen,
                                           size_t uPos)
{
   UsefulBufC Data = {pBytes, uLen};
   UsefulOutBuf_InsertUsefulBuf(pMe, Data, uPos);
}


static inline void UsefulOutBuf_InsertString(UsefulOutBuf *pMe,
                                             const char *szString,
                                             size_t uPos)
{
   UsefulBufC UBC;
   UBC.ptr = szString;
   UBC.len = strlen(szString);

   UsefulOutBuf_InsertUsefulBuf(pMe, UBC, uPos);
}


static inline void UsefulOutBuf_InsertByte(UsefulOutBuf *me,
                                           uint8_t byte,
                                           size_t uPos)
{
   UsefulOutBuf_InsertData(me, &byte, 1, uPos);
}


static inline void UsefulOutBuf_InsertUint16(UsefulOutBuf *me,
                                             uint16_t uInteger16,
                                             size_t uPos)
{
   /* See UsefulOutBuf_InsertUint64() for comments on this code */

   const void *pBytes;

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN)
   pBytes = &uInteger16;

#elif defined(USEFULBUF_CONFIG_HTON)
   uint16_t uTmp = htons(uInteger16);
   pBytes        = &uTmp;

#elif defined(USEFULBUF_CONFIG_LITTLE_ENDIAN) && defined(USEFULBUF_CONFIG_BSWAP)
   uint16_t uTmp = __builtin_bswap16(uInteger16);
   pBytes = &uTmp;

#else
   uint8_t aTmp[2];

   aTmp[0] = (uint8_t)((uInteger16 & 0xff00) >> 8);
   aTmp[1] = (uint8_t)(uInteger16 & 0xff);

   pBytes = aTmp;
#endif

   UsefulOutBuf_InsertData(me, pBytes, 2, uPos);
}


static inline void UsefulOutBuf_InsertUint32(UsefulOutBuf *pMe,
                                             uint32_t uInteger32,
                                             size_t uPos)
{
   /* See UsefulOutBuf_InsertUint64() for comments on this code */

   const void *pBytes;

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN)
   pBytes = &uInteger32;

#elif defined(USEFULBUF_CONFIG_HTON)
   uint32_t uTmp = htonl(uInteger32);
   pBytes = &uTmp;

#elif defined(USEFULBUF_CONFIG_LITTLE_ENDIAN) && defined(USEFULBUF_CONFIG_BSWAP)
   uint32_t uTmp = __builtin_bswap32(uInteger32);

   pBytes = &uTmp;

#else
   uint8_t aTmp[4];

   aTmp[0] = (uint8_t)((uInteger32 & 0xff000000) >> 24);
   aTmp[1] = (uint8_t)((uInteger32 & 0xff0000) >> 16);
   aTmp[2] = (uint8_t)((uInteger32 & 0xff00) >> 8);
   aTmp[3] = (uint8_t)(uInteger32 & 0xff);

   pBytes = aTmp;
#endif

   UsefulOutBuf_InsertData(pMe, pBytes, 4, uPos);
}

static inline void UsefulOutBuf_InsertUint64(UsefulOutBuf *pMe,
                                             uint64_t      uInteger64,
                                             size_t        uPos)
{
   const void *pBytes;

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN)
   /* We have been told explicitly we are running on a big-endian
    * machine. Network byte order is big endian, so just copy.  There
    * is no issue with alignment here because uInteger64 is always
    * aligned (and it doesn't matter if pBytes is aligned).
    */
   pBytes = &uInteger64;

#elif defined(USEFULBUF_CONFIG_HTON)
   /* Use system function to handle big- and little-endian. This works
    * on both big- and little-endian machines, but hton() is not
    * always available or in a standard place so it is not used by
    * default. With some compilers and CPUs the code for this is very
    * compact through use of a special swap instruction and on
    * big-endian machines hton() will reduce to nothing.
    */
   uint64_t uTmp = htonll(uInteger64);

   pBytes = &uTmp;

#elif defined(USEFULBUF_CONFIG_LITTLE_ENDIAN) && defined(USEFULBUF_CONFIG_BSWAP)
   /* Use built-in function for byte swapping. This usually compiles
    * to an efficient special byte swap instruction. Unlike hton() it
    * does not do this conditionally on the CPU endianness, so this
    * code is also conditional on USEFULBUF_CONFIG_LITTLE_ENDIAN
    */
   uint64_t uTmp = __builtin_bswap64(uInteger64);

   pBytes = &uTmp;

#else
   /* Default which works on every CPU with no dependency on anything
    * from the CPU, compiler, libraries or OS.  This always works, but
    * it is usually a little larger and slower than hton().
    */
   uint8_t aTmp[8];

   aTmp[0] = (uint8_t)((uInteger64 & 0xff00000000000000) >> 56);
   aTmp[1] = (uint8_t)((uInteger64 & 0xff000000000000) >> 48);
   aTmp[2] = (uint8_t)((uInteger64 & 0xff0000000000) >> 40);
   aTmp[3] = (uint8_t)((uInteger64 & 0xff00000000) >> 32);
   aTmp[4] = (uint8_t)((uInteger64 & 0xff000000) >> 24);
   aTmp[5] = (uint8_t)((uInteger64 & 0xff0000) >> 16);
   aTmp[6] = (uint8_t)((uInteger64 & 0xff00) >> 8);
   aTmp[7] = (uint8_t)(uInteger64 & 0xff);

   pBytes = aTmp;
#endif

   /* Do the insert */
   UsefulOutBuf_InsertData(pMe, pBytes, sizeof(uint64_t), uPos);
}


#ifndef USEFULBUF_DISABLE_ALL_FLOAT
static inline void UsefulOutBuf_InsertFloat(UsefulOutBuf *pMe,
                                            float f,
                                            size_t uPos)
{
   UsefulOutBuf_InsertUint32(pMe, UsefulBufUtil_CopyFloatToUint32(f), uPos);
}


static inline void UsefulOutBuf_InsertDouble(UsefulOutBuf *pMe,
                                             double d,
                                             size_t uPos)
{
   UsefulOutBuf_InsertUint64(pMe, UsefulBufUtil_CopyDoubleToUint64(d), uPos);
}
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */


static inline void UsefulOutBuf_AppendUsefulBuf(UsefulOutBuf *pMe,
                                                UsefulBufC NewData)
{
   /* An append is just a insert at the end */
   UsefulOutBuf_InsertUsefulBuf(pMe, NewData, UsefulOutBuf_GetEndPosition(pMe));
}


static inline void UsefulOutBuf_AppendData(UsefulOutBuf *pMe,
                                           const void *pBytes,
                                           size_t uLen)
{
   UsefulBufC Data = {pBytes, uLen};
   UsefulOutBuf_AppendUsefulBuf(pMe, Data);
}


static inline void UsefulOutBuf_AppendString(UsefulOutBuf *pMe,
                                             const char *szString)
{
   UsefulBufC UBC;
   UBC.ptr = szString;
   UBC.len = strlen(szString);

   UsefulOutBuf_AppendUsefulBuf(pMe, UBC);
}


static inline void UsefulOutBuf_AppendByte(UsefulOutBuf *pMe,
                                           uint8_t byte)
{
   UsefulOutBuf_AppendData(pMe, &byte, 1);
}


static inline void UsefulOutBuf_AppendUint16(UsefulOutBuf *pMe,
                                             uint16_t uInteger16)
{
   UsefulOutBuf_InsertUint16(pMe, uInteger16, UsefulOutBuf_GetEndPosition(pMe));
}

static inline void UsefulOutBuf_AppendUint32(UsefulOutBuf *pMe,
                                             uint32_t uInteger32)
{
   UsefulOutBuf_InsertUint32(pMe, uInteger32, UsefulOutBuf_GetEndPosition(pMe));
}


static inline void UsefulOutBuf_AppendUint64(UsefulOutBuf *pMe,
                                             uint64_t uInteger64)
{
   UsefulOutBuf_InsertUint64(pMe, uInteger64, UsefulOutBuf_GetEndPosition(pMe));
}


#ifndef USEFULBUF_DISABLE_ALL_FLOAT
static inline void UsefulOutBuf_AppendFloat(UsefulOutBuf *pMe,
                                            float f)
{
   UsefulOutBuf_InsertFloat(pMe, f, UsefulOutBuf_GetEndPosition(pMe));
}


static inline void UsefulOutBuf_AppendDouble(UsefulOutBuf *pMe,
                                             double d)
{
   UsefulOutBuf_InsertDouble(pMe, d, UsefulOutBuf_GetEndPosition(pMe));
}
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */


static inline int UsefulOutBuf_GetError(UsefulOutBuf *pMe)
{
   return pMe->err;
}


static inline size_t UsefulOutBuf_RoomLeft(UsefulOutBuf *pMe)
{
   return pMe->UB.len - pMe->data_len;
}


static inline int UsefulOutBuf_WillItFit(UsefulOutBuf *pMe, size_t uLen)
{
   return uLen <= UsefulOutBuf_RoomLeft(pMe);
}


static inline int UsefulOutBuf_IsBufferNULL(UsefulOutBuf *pMe)
{
   return pMe->UB.ptr == NULL;
}


static inline UsefulBuf UsefulOutBuf_GetOutPlace(UsefulOutBuf *pUOutBuf)
{
   UsefulBuf R;

   R.len = UsefulOutBuf_RoomLeft(pUOutBuf);
   if(R.len > 0 && pUOutBuf->UB.ptr != NULL) {
      R.ptr = (uint8_t *)pUOutBuf->UB.ptr + pUOutBuf->data_len;
   } else {
      R.ptr = NULL;
   }

   return R;
}


static inline UsefulBuf UsefulOutBuf_RetrieveOutputStorage(UsefulOutBuf *pMe)
{
   return pMe->UB;
}




static inline void UsefulInputBuf_Init(UsefulInputBuf *pMe, UsefulBufC UB)
{
   pMe->cursor = 0;
   pMe->err    = 0;
   pMe->magic  = UIB_MAGIC;
   pMe->UB     = UB;
}

static inline size_t UsefulInputBuf_Tell(UsefulInputBuf *pMe)
{
   return pMe->cursor;
}


static inline size_t UsefulInputBuf_GetBufferLength(UsefulInputBuf *pMe)
{
    return pMe->UB.len;
}


static inline void UsefulInputBuf_Seek(UsefulInputBuf *pMe, size_t uPos)
{
   if(uPos > pMe->UB.len) {
      pMe->err = 1;
   } else {
      pMe->cursor = uPos;
   }
}


static inline size_t UsefulInputBuf_BytesUnconsumed(UsefulInputBuf *pMe)
{
   /* Code Reviewers: THIS FUNCTION DOES POINTER MATH */

   /* Magic number is messed up. Either the structure got overwritten
    * or was never initialized.
    */
   if(pMe->magic != UIB_MAGIC) {
      return 0;
   }

   /* The cursor is off the end of the input buffer given.
    * Presuming there are no bugs in this code, this should never happen.
    * If it is so, the struct was corrupted. The check is retained as
    * as a defense in case there is a bug in this code or the struct is
    * corrupted by an attacker or accidentally.
    */
   if(pMe->cursor > pMe->UB.len) {
      return 0;
   }

   /* subtraction can't go negative because of check above */
   return pMe->UB.len - pMe->cursor;
}


static inline int UsefulInputBuf_BytesAvailable(UsefulInputBuf *pMe, size_t uLen)
{
   return UsefulInputBuf_BytesUnconsumed(pMe) >= uLen ? 1 : 0;
}


static inline size_t UsefulInputBuf_PointerToOffset(UsefulInputBuf *pUInBuf, const void *p)
{
   return UsefulBuf_PointerToOffset(pUInBuf->UB, p);
}


static inline const void *UsefulInputBuf_OffsetToPointer(UsefulInputBuf *pUInBuf, size_t uOffset)
 {
    return UsefulBuf_OffsetToPointer(pUInBuf->UB, uOffset);
 }


static inline UsefulBufC UsefulInputBuf_GetUsefulBuf(UsefulInputBuf *pMe, size_t uNum)
{
   const void *pResult = UsefulInputBuf_GetBytes(pMe, uNum);
   if(!pResult) {
      return NULLUsefulBufC;
   } else {
      UsefulBufC UBC;
      UBC.ptr = pResult;
      UBC.len = uNum;
      return UBC;
   }
}


static inline uint8_t UsefulInputBuf_GetByte(UsefulInputBuf *pMe)
{
   const void *pResult = UsefulInputBuf_GetBytes(pMe, sizeof(uint8_t));

   /* The ternary operator is subject to integer promotion, because
    * the operands are smaller than int, so cast back to uint8_t is
    * needed to be completely explicit about types (for static
    * analyzers).
    */
   return (uint8_t)(pResult ? *(const uint8_t *)pResult : 0);
}

static inline uint16_t UsefulInputBuf_GetUint16(UsefulInputBuf *pMe)
{
   const uint8_t *pResult = (const uint8_t *)UsefulInputBuf_GetBytes(pMe, sizeof(uint16_t));

   if(!pResult) {
      return 0;
   }

   /* See UsefulInputBuf_GetUint64() for comments on this code */
#if defined(USEFULBUF_CONFIG_BIG_ENDIAN) || defined(USEFULBUF_CONFIG_HTON) || defined(USEFULBUF_CONFIG_BSWAP)
   uint16_t uTmp;
   memcpy(&uTmp, pResult, sizeof(uint16_t));

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN)
   return uTmp;

#elif defined(USEFULBUF_CONFIG_HTON)
   return ntohs(uTmp);

#else
   return __builtin_bswap16(uTmp);

#endif

#else

   /* The operations here are subject to integer promotion because the
    * operands are smaller than int. They will be promoted to unsigned
    * int for the shift and addition. The cast back to uint16_t is is
    * needed to be completely explicit about types (for static
    * analyzers).
    */
   return (uint16_t)((pResult[0] << 8) + pResult[1]);

#endif
}


static inline uint32_t UsefulInputBuf_GetUint32(UsefulInputBuf *pMe)
{
   const uint8_t *pResult = (const uint8_t *)UsefulInputBuf_GetBytes(pMe, sizeof(uint32_t));

   if(!pResult) {
      return 0;
   }

   /* See UsefulInputBuf_GetUint64() for comments on this code */
#if defined(USEFULBUF_CONFIG_BIG_ENDIAN) || defined(USEFULBUF_CONFIG_HTON) || defined(USEFULBUF_CONFIG_BSWAP)
   uint32_t uTmp;
   memcpy(&uTmp, pResult, sizeof(uint32_t));

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN)
   return uTmp;

#elif defined(USEFULBUF_CONFIG_HTON)
   return ntohl(uTmp);

#else
   return __builtin_bswap32(uTmp);

#endif

#else
   return ((uint32_t)pResult[0]<<24) +
          ((uint32_t)pResult[1]<<16) +
          ((uint32_t)pResult[2]<<8)  +
           (uint32_t)pResult[3];
#endif
}


static inline uint64_t UsefulInputBuf_GetUint64(UsefulInputBuf *pMe)
{
   const uint8_t *pResult = (const uint8_t *)UsefulInputBuf_GetBytes(pMe, sizeof(uint64_t));

   if(!pResult) {
      return 0;
   }

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN) || defined(USEFULBUF_CONFIG_HTON) || defined(USEFULBUF_CONFIG_BSWAP)
   /* pResult will probably not be aligned.  This memcpy() moves the
    * bytes into a temp variable safely for CPUs that can or can't do
    * unaligned memory access. Many compilers will optimize the
    * memcpy() into a simple move instruction.
    */
   uint64_t uTmp;
   memcpy(&uTmp, pResult, sizeof(uint64_t));

#if defined(USEFULBUF_CONFIG_BIG_ENDIAN)
   /* We have been told expliclity this is a big-endian CPU.  Since
    * network byte order is big-endian, there is nothing to do.
    */

   return uTmp;

#elif defined(USEFULBUF_CONFIG_HTON)
   /* We have been told to use ntoh(), the system function to handle
    * big- and little-endian. This works on both big- and
    * little-endian machines, but ntoh() is not always available or in
    * a standard place so it is not used by default. On some CPUs the
    * code for this is very compact through use of a special swap
    * instruction.
    */

   return ntohll(uTmp);

#else
   /* Little-endian (since it is not USEFULBUF_CONFIG_BIG_ENDIAN) and
    * USEFULBUF_CONFIG_BSWAP (since it is not USEFULBUF_CONFIG_HTON).
    * __builtin_bswap64() and friends are not conditional on CPU
    * endianness so this must only be used on little-endian machines.
    */

   return __builtin_bswap64(uTmp);


#endif

#else
   /* This is the default code that works on every CPU and every
    * endianness with no dependency on ntoh().  This works on CPUs
    * that either allow or do not allow unaligned access. It will
    * always work, but usually is a little less efficient than ntoh().
    */

   return   ((uint64_t)pResult[0]<<56) +
            ((uint64_t)pResult[1]<<48) +
            ((uint64_t)pResult[2]<<40) +
            ((uint64_t)pResult[3]<<32) +
            ((uint64_t)pResult[4]<<24) +
            ((uint64_t)pResult[5]<<16) +
            ((uint64_t)pResult[6]<<8)  +
            (uint64_t)pResult[7];
#endif
}


#ifndef USEFULBUF_DISABLE_ALL_FLOAT
static inline float UsefulInputBuf_GetFloat(UsefulInputBuf *pMe)
{
   uint32_t uResult = UsefulInputBuf_GetUint32(pMe);

   return uResult ? UsefulBufUtil_CopyUint32ToFloat(uResult) : 0;
}


static inline double UsefulInputBuf_GetDouble(UsefulInputBuf *pMe)
{
   uint64_t uResult = UsefulInputBuf_GetUint64(pMe);

   return uResult ? UsefulBufUtil_CopyUint64ToDouble(uResult) : 0;
}
#endif /* USEFULBUF_DISABLE_ALL_FLOAT */


static inline int UsefulInputBuf_GetError(UsefulInputBuf *pMe)
{
   return pMe->err;
}


static inline void UsefulInputBuf_SetBufferLength(UsefulInputBuf *pMe, size_t uNewLen)
{
    pMe->UB.len = uNewLen;
}

static inline UsefulBufC UsefulInputBuf_RetrieveUndecodedInput(UsefulInputBuf *pMe)
{
   return pMe->UB;
}


#ifdef __cplusplus
}
#endif

#endif  /* _UsefulBuf_h */