include/mbedtls/constant_time.h

/**
 *  Constant-time functions
 */
/*
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

#ifndef MBEDTLS_CONSTANT_TIME_H
#define MBEDTLS_CONSTANT_TIME_H

#include <stddef.h>

#ifdef __GNUC__
    #pragma GCC diagnostic push
    #pragma GCC diagnostic ignored "-Wredundant-decls"
#endif

/** Constant-time buffer comparison without branches.
 *
 * This is equivalent to the standard memcmp function, but is likely to be
 * compiled to code using bitwise operation rather than a branch.
 *
 * This function can be used to write constant-time code by replacing branches
 * with bit operations using masks.
 *
 * \param a     Pointer to the first buffer.
 * \param b     Pointer to the second buffer.
 * \param n     The number of bytes to compare in the buffer.
 *
 * \return      Zero if the content of the two buffer is the same,
 *              otherwise non-zero.
 */
int mbedtls_ct_memcmp(const void *a,
                      const void *b,
                      size_t n);

#ifdef __GNUC__
    #pragma GCC diagnostic pop
#endif

#endif /* MBEDTLS_CONSTANT_TIME_H */