From 2143a4ad1fc79e3e601e078f86aafcb6fbabcc71 Mon Sep 17 00:00:00 2001 From: Dave Rodgman Date: Fri, 19 Jan 2024 14:08:17 +0000 Subject: [PATCH] Improve mbedtls_xor docs Signed-off-by: Dave Rodgman --- library/common.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/library/common.h b/library/common.h index 760dff49e..3b1c7e1e7 100644 --- a/library/common.h +++ b/library/common.h @@ -174,6 +174,14 @@ __attribute__((always_inline)) * \param a Pointer to input (buffer of at least \p n bytes) * \param b Pointer to input (buffer of at least \p n bytes) * \param n Number of bytes to process. + * + * \note Depending on the situation, it may be faster to use either mbedtls_xor or + * mbedtls_xor_no_simd (these are functionally equivalent). + * If the result is used immediately after the xor operation in non-SIMD code (e.g, in + * AES-CBC), there may be additional latency to transfer the data from SIMD to scalar + * registers, and in this case, mbedtls_xor_no_simd may be faster. In other cases where + * the result is not used immediately (e.g., in AES-CTR), mbedtls_xor may be faster. + * For targets without SIMD support, they will behave the same. */ static inline void mbedtls_xor(unsigned char *r, const unsigned char *a, @@ -238,6 +246,14 @@ __attribute__((always_inline)) * \param a Pointer to input (buffer of at least \p n bytes) * \param b Pointer to input (buffer of at least \p n bytes) * \param n Number of bytes to process. + * + * \note Depending on the situation, it may be faster to use either mbedtls_xor or + * mbedtls_xor_no_simd (these are functionally equivalent). + * If the result is used immediately after the xor operation in non-SIMD code (e.g, in + * AES-CBC), there may be additional latency to transfer the data from SIMD to scalar + * registers, and in this case, mbedtls_xor_no_simd may be faster. In other cases where + * the result is not used immediately (e.g., in AES-CTR), mbedtls_xor may be faster. + * For targets without SIMD support, they will behave the same. */ static inline void mbedtls_xor_no_simd(unsigned char *r, const unsigned char *a,