FFmpeg  5.1
murmur3.h
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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 */
struct AVMurMur3 * av_murmur3_alloc(void)
Allocate an AVMurMur3 hash context.
void av_murmur3_update(struct AVMurMur3 *c, const uint8_t *src, size_t len)
Update hash context with new data.
void av_murmur3_init(struct AVMurMur3 *c)
Initialize or reinitialize an AVMurMur3 hash context.
void av_murmur3_init_seeded(struct AVMurMur3 *c, uint64_t seed)
Initialize or reinitialize an AVMurMur3 hash context with a seed.
void av_murmur3_final(struct AVMurMur3 *c, uint8_t dst[16])
Finish hashing and output digest value.