murmur3.h (3507B)
1 /* 2 * Copyright (C) 2013 Reimar Döffinger <Reimar.Doeffinger@gmx.de> 3 * 4 * This file is part of FFmpeg. 5 * 6 * FFmpeg is free software; you can redistribute it and/or 7 * modify it under the terms of the GNU Lesser General Public 8 * License as published by the Free Software Foundation; either 9 * version 2.1 of the License, or (at your option) any later version. 10 * 11 * FFmpeg is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 * Lesser General Public License for more details. 15 * 16 * You should have received a copy of the GNU Lesser General Public 17 * License along with FFmpeg; if not, write to the Free Software 18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 19 */ 20 21 /** 22 * @file 23 * @ingroup lavu_murmur3 24 * Public header for MurmurHash3 hash function implementation. 25 */ 26 27 #ifndef AVUTIL_MURMUR3_H 28 #define AVUTIL_MURMUR3_H 29 30 #include <stddef.h> 31 #include <stdint.h> 32 33 /** 34 * @defgroup lavu_murmur3 Murmur3 35 * @ingroup lavu_hash 36 * MurmurHash3 hash function implementation. 37 * 38 * MurmurHash3 is a non-cryptographic hash function, of which three 39 * incompatible versions were created by its inventor Austin Appleby: 40 * 41 * - 32-bit output 42 * - 128-bit output for 32-bit platforms 43 * - 128-bit output for 64-bit platforms 44 * 45 * FFmpeg only implements the last variant: 128-bit output designed for 64-bit 46 * platforms. Even though the hash function was designed for 64-bit platforms, 47 * the function in reality works on 32-bit systems too, only with reduced 48 * performance. 49 * 50 * @anchor lavu_murmur3_seedinfo 51 * By design, MurmurHash3 requires a seed to operate. In response to this, 52 * libavutil provides two functions for hash initiation, one that requires a 53 * seed (av_murmur3_init_seeded()) and one that uses a fixed arbitrary integer 54 * as the seed, and therefore does not (av_murmur3_init()). 55 * 56 * To make hashes comparable, you should provide the same seed for all calls to 57 * this hash function -- if you are supplying one yourself, that is. 58 * 59 * @{ 60 */ 61 62 /** 63 * Allocate an AVMurMur3 hash context. 64 * 65 * @return Uninitialized hash context or `NULL` in case of error 66 */ 67 struct AVMurMur3 *av_murmur3_alloc(void); 68 69 /** 70 * Initialize or reinitialize an AVMurMur3 hash context with a seed. 71 * 72 * @param[out] c Hash context 73 * @param[in] seed Random seed 74 * 75 * @see av_murmur3_init() 76 * @see @ref lavu_murmur3_seedinfo "Detailed description" on a discussion of 77 * seeds for MurmurHash3. 78 */ 79 void av_murmur3_init_seeded(struct AVMurMur3 *c, uint64_t seed); 80 81 /** 82 * Initialize or reinitialize an AVMurMur3 hash context. 83 * 84 * Equivalent to av_murmur3_init_seeded() with a built-in seed. 85 * 86 * @param[out] c Hash context 87 * 88 * @see av_murmur3_init_seeded() 89 * @see @ref lavu_murmur3_seedinfo "Detailed description" on a discussion of 90 * seeds for MurmurHash3. 91 */ 92 void av_murmur3_init(struct AVMurMur3 *c); 93 94 /** 95 * Update hash context with new data. 96 * 97 * @param[out] c Hash context 98 * @param[in] src Input data to update hash with 99 * @param[in] len Number of bytes to read from `src` 100 */ 101 void av_murmur3_update(struct AVMurMur3 *c, const uint8_t *src, size_t len); 102 103 /** 104 * Finish hashing and output digest value. 105 * 106 * @param[in,out] c Hash context 107 * @param[out] dst Buffer where output digest value is stored 108 */ 109 void av_murmur3_final(struct AVMurMur3 *c, uint8_t dst[16]); 110 111 /** 112 * @} 113 */ 114 115 #endif /* AVUTIL_MURMUR3_H */