Consistently use \c NULL and \c 0
diff --git a/include/mbedtls/ctr_drbg.h b/include/mbedtls/ctr_drbg.h
index f65606e..e47b769 100644
--- a/include/mbedtls/ctr_drbg.h
+++ b/include/mbedtls/ctr_drbg.h
@@ -232,7 +232,7 @@
* length of the buffer.
* \param p_entropy The entropy context to pass to \p f_entropy.
* \param custom Personalization data, that is device-specific
- * identifiers. This can be NULL, in which case the
+ * identifiers. This can be \c NULL, in which case the
* personalization data is empty regardless of the value
* of \p len.
* \param len The length of the personalization data.
@@ -330,7 +330,7 @@
* extracts data from the entropy source.
*
* \param ctx The CTR_DRBG context.
- * \param additional Additional data to add to the state. Can be NULL.
+ * \param additional Additional data to add to the state. Can be \c NULL.
* \param len The length of the additional data.
* This must be less than
* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
@@ -348,7 +348,7 @@
*
* \param ctx The CTR_DRBG context.
* \param additional The data to update the state with. This must not be
- * null unless \p add_len is 0.
+ * \c NULL unless \p add_len is \c 0.
* \param add_len Length of \p additional in bytes. This must be at
* most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
*
@@ -372,11 +372,11 @@
* #mbedtls_ctr_drbg_context structure.
* \param output The buffer to fill.
* \param output_len The length of the buffer in bytes.
- * \param additional Additional data to update. Can be NULL, in which
+ * \param additional Additional data to update. Can be \c NULL, in which
* case the additional data is empty regardless of
* the value of \p add_len.
* \param add_len The length of the additional data
- * if \p additional is non-null.
+ * if \p additional is not \c NULL.
* This must be less than #MBEDTLS_CTR_DRBG_MAX_INPUT
* and less than
* #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len