FFmpeg  4.0
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 <stdint.h>
31 
32 #include "version.h"
33 
34 /**
35  * @defgroup lavu_murmur3 Murmur3
36  * @ingroup lavu_hash
37  * MurmurHash3 hash function implementation.
38  *
39  * MurmurHash3 is a non-cryptographic hash function, of which three
40  * incompatible versions were created by its inventor Austin Appleby:
41  *
42  * - 32-bit output
43  * - 128-bit output for 32-bit platforms
44  * - 128-bit output for 64-bit platforms
45  *
46  * FFmpeg only implements the last variant: 128-bit output designed for 64-bit
47  * platforms. Even though the hash function was designed for 64-bit platforms,
48  * the function in reality works on 32-bit systems too, only with reduced
49  * performance.
50  *
51  * @anchor lavu_murmur3_seedinfo
52  * By design, MurmurHash3 requires a seed to operate. In response to this,
53  * libavutil provides two functions for hash initiation, one that requires a
54  * seed (av_murmur3_init_seeded()) and one that uses a fixed arbitrary integer
55  * as the seed, and therefore does not (av_murmur3_init()).
56  *
57  * To make hashes comparable, you should provide the same seed for all calls to
58  * this hash function -- if you are supplying one yourself, that is.
59  *
60  * @{
61  */
62 
63 /**
64  * Allocate an AVMurMur3 hash context.
65  *
66  * @return Uninitialized hash context or `NULL` in case of error
67  */
68 struct AVMurMur3 *av_murmur3_alloc(void);
69 
70 /**
71  * Initialize or reinitialize an AVMurMur3 hash context with a seed.
72  *
73  * @param[out] c Hash context
74  * @param[in] seed Random seed
75  *
76  * @see av_murmur3_init()
77  * @see @ref lavu_murmur3_seedinfo "Detailed description" on a discussion of
78  * seeds for MurmurHash3.
79  */
80 void av_murmur3_init_seeded(struct AVMurMur3 *c, uint64_t seed);
81 
82 /**
83  * Initialize or reinitialize an AVMurMur3 hash context.
84  *
85  * Equivalent to av_murmur3_init_seeded() with a built-in seed.
86  *
87  * @param[out] c Hash context
88  *
89  * @see av_murmur3_init_seeded()
90  * @see @ref lavu_murmur3_seedinfo "Detailed description" on a discussion of
91  * seeds for MurmurHash3.
92  */
93 void av_murmur3_init(struct AVMurMur3 *c);
94 
95 /**
96  * Update hash context with new data.
97  *
98  * @param[out] c Hash context
99  * @param[in] src Input data to update hash with
100  * @param[in] len Number of bytes to read from `src`
101  */
102 #if FF_API_CRYPTO_SIZE_T
103 void av_murmur3_update(struct AVMurMur3 *c, const uint8_t *src, int len);
104 #else
105 void av_murmur3_update(struct AVMurMur3 *c, const uint8_t *src, size_t len);
106 #endif
107 
108 /**
109  * Finish hashing and output digest value.
110  *
111  * @param[in,out] c Hash context
112  * @param[out] dst Buffer where output digest value is stored
113  */
114 void av_murmur3_final(struct AVMurMur3 *c, uint8_t dst[16]);
115 
116 /**
117  * @}
118  */
119 
120 #endif /* AVUTIL_MURMUR3_H */
void av_murmur3_init_seeded(struct AVMurMur3 *c, uint64_t seed)
Initialize or reinitialize an AVMurMur3 hash context with a seed.
Definition: murmur3.c:37
#define src
Definition: vp8dsp.c:254
uint8_t
void av_murmur3_init(struct AVMurMur3 *c)
Initialize or reinitialize an AVMurMur3 hash context.
Definition: murmur3.c:43
Libavutil version macros.
static unsigned int seed
Definition: videogen.c:78
void av_murmur3_update(struct AVMurMur3 *c, const uint8_t *src, int len)
Update hash context with new data.
Definition: murmur3.c:93
static double c[64]
int len
struct AVMurMur3 * av_murmur3_alloc(void)
Allocate an AVMurMur3 hash context.
Definition: murmur3.c:32
void av_murmur3_final(struct AVMurMur3 *c, uint8_t dst[16])
Finish hashing and output digest value.
Definition: murmur3.c:145