1 /**
2  * \file ctr.h
3  *
4  * \brief    This file contains common functionality for counter algorithms.
5  *
6  *  Copyright The Mbed TLS Contributors
7  *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
8  */
9 
10 #ifndef MBEDTLS_CTR_H
11 #define MBEDTLS_CTR_H
12 
13 #include "common.h"
14 
15 /**
16  * \brief               Increment a big-endian 16-byte value.
17  *                      This is quite performance-sensitive for AES-CTR and CTR-DRBG.
18  *
19  * \param n             A 16-byte value to be incremented.
20  */
mbedtls_ctr_increment_counter(uint8_t n[16])21 static inline void mbedtls_ctr_increment_counter(uint8_t n[16])
22 {
23     // The 32-bit version seems to perform about the same as a 64-bit version
24     // on 64-bit architectures, so no need to define a 64-bit version.
25     for (int i = 3;; i--) {
26         uint32_t x = MBEDTLS_GET_UINT32_BE(n, i << 2);
27         x += 1;
28         MBEDTLS_PUT_UINT32_BE(x, n, i << 2);
29         if (x != 0 || i == 0) {
30             break;
31         }
32     }
33 }
34 
35 #endif /* MBEDTLS_CTR_H */
36