Make functions static
These functions are only used as an auxiliary function for constant-time functions.
Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/constant_time.c b/library/constant_time.c
index 4fad1b2..6e8a7c2 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -167,8 +167,19 @@
return( 1 ^ diff1 );
}
-unsigned mbedtls_cf_size_gt( size_t x,
- size_t y )
+/** Constant-flow "greater than" comparison:
+ * return x > y
+ *
+ * This is equivalent to \p x > \p y, but is likely to be compiled
+ * to code using bitwise operation rather than a branch.
+ *
+ * \param x The first value to analyze.
+ * \param y The second value to analyze.
+ *
+ * \return 1 if \p x greater than \p y, otherwise 0.
+ */
+static unsigned mbedtls_cf_size_gt( size_t x,
+ size_t y )
{
/* Return the sign bit (1 for negative) of (y - x). */
return( ( y - x ) >> ( sizeof( size_t ) * 8 - 1 ) );
@@ -214,17 +225,42 @@
return( ( mask & if1 ) | (~mask & if0 ) );
}
-size_t mbedtls_cf_size_if( unsigned condition,
- size_t if1,
- size_t if0 )
+/** Choose between two integer values without branches.
+ *
+ * This is equivalent to `condition ? if1 : if0`, but is likely to be compiled
+ * to code using bitwise operation rather than a branch.
+ *
+ * \param condition Condition to test.
+ * \param if1 Value to use if \p condition is nonzero.
+ * \param if0 Value to use if \p condition is zero.
+ *
+ * \return \c if1 if \p condition is nonzero, otherwise \c if0.
+ */
+static size_t mbedtls_cf_size_if( unsigned condition,
+ size_t if1,
+ size_t if0 )
{
size_t mask = mbedtls_cf_size_mask( condition );
return( ( mask & if1 ) | (~mask & if0 ) );
}
-int mbedtls_cf_cond_select_sign( unsigned char condition,
- int if1,
- int if0 )
+/** Select between two sign values witout branches.
+ *
+ * This is functionally equivalent to `condition ? if1 : if0` but uses only bit
+ * operations in order to avoid branches.
+ *
+ * \note if1 and if0 must be either 1 or -1, otherwise the result
+ * is undefined.
+ *
+ * \param condition Condition to test.
+ * \param if1 The first sign; must be either +1 or -1.
+ * \param if0 The second sign; must be either +1 or -1.
+ *
+ * \return \c if1 if \p condition is nonzero, otherwise \c if0.
+ * */
+static int mbedtls_cf_cond_select_sign( unsigned char condition,
+ int if1,
+ int if0 )
{
/* In order to avoid questions about what we can reasonnably assume about
* the representations of signed integers, move everything to unsigned
@@ -271,9 +307,25 @@
#endif /* MBEDTLS_BIGNUM_C */
-void mbedtls_cf_mem_move_to_left( void *start,
- size_t total,
- size_t offset )
+/** Shift some data towards the left inside a buffer.
+ *
+ * `mbedtls_cf_mem_move_to_left(start, total, offset)` is functionally
+ * equivalent to
+ * ```
+ * memmove(start, start + offset, total - offset);
+ * memset(start + offset, 0, total - offset);
+ * ```
+ * but it strives to use a memory access pattern (and thus total timing)
+ * that does not depend on \p offset. This timing independence comes at
+ * the expense of performance.
+ *
+ * \param start Pointer to the start of the buffer.
+ * \param total Total size of the buffer.
+ * \param offset Offset from which to copy \p total - \p offset bytes.
+ */
+static void mbedtls_cf_mem_move_to_left( void *start,
+ size_t total,
+ size_t offset )
{
volatile unsigned char *buf = start;
size_t i, n;
diff --git a/library/constant_time.h b/library/constant_time.h
index 11a07f3..6dfac8b 100644
--- a/library/constant_time.h
+++ b/library/constant_time.h
@@ -122,19 +122,6 @@
unsigned mbedtls_cf_size_bool_eq( size_t x,
size_t y );
-/** Constant-flow "greater than" comparison:
- * return x > y
- *
- * This is equivalent to \p x > \p y, but is likely to be compiled
- * to code using bitwise operation rather than a branch.
- *
- * \param x The first value to analyze.
- * \param y The second value to analyze.
- *
- * \return 1 if \p x greater than \p y, otherwise 0.
- */
-unsigned mbedtls_cf_size_gt( size_t x,
- size_t y );
#if defined(MBEDTLS_BIGNUM_C)
@@ -168,38 +155,6 @@
unsigned if1,
unsigned if0 );
-/** Choose between two integer values without branches.
- *
- * This is equivalent to `condition ? if1 : if0`, but is likely to be compiled
- * to code using bitwise operation rather than a branch.
- *
- * \param condition Condition to test.
- * \param if1 Value to use if \p condition is nonzero.
- * \param if0 Value to use if \p condition is zero.
- *
- * \return \c if1 if \p condition is nonzero, otherwise \c if0.
- */
-size_t mbedtls_cf_size_if( unsigned condition,
- size_t if1,
- size_t if0 );
-
-/** Select between two sign values witout branches.
- *
- * This is functionally equivalent to `condition ? if1 : if0` but uses only bit
- * operations in order to avoid branches.
- *
- * \note if1 and if0 must be either 1 or -1, otherwise the result
- * is undefined.
- *
- * \param condition Condition to test.
- * \param if1 The first sign; must be either +1 or -1.
- * \param if0 The second sign; must be either +1 or -1.
- *
- * \return \c if1 if \p condition is nonzero, otherwise \c if0. */
-int mbedtls_cf_cond_select_sign( unsigned char condition,
- int if1,
- int if0 );
-
#if defined(MBEDTLS_BIGNUM_C)
/** Conditionally assign a value without branches.
@@ -222,26 +177,6 @@
#endif /* MBEDTLS_BIGNUM_C */
-/** Shift some data towards the left inside a buffer.
- *
- * `mbedtls_cf_mem_move_to_left(start, total, offset)` is functionally
- * equivalent to
- * ```
- * memmove(start, start + offset, total - offset);
- * memset(start + offset, 0, total - offset);
- * ```
- * but it strives to use a memory access pattern (and thus total timing)
- * that does not depend on \p offset. This timing independence comes at
- * the expense of performance.
- *
- * \param start Pointer to the start of the buffer.
- * \param total Total size of the buffer.
- * \param offset Offset from which to copy \p total - \p offset bytes.
- */
-void mbedtls_cf_mem_move_to_left( void *start,
- size_t total,
- size_t offset );
-
/** Conditional memcpy without branches.
*
* This is equivalent to `if ( c1 == c2 ) memcpy(dst, src, len)`, but is likely