aboutsummaryrefslogtreecommitdiffstats
path: root/libavutil/murmur3.c
blob: 701fa6a0ff1652df0de0064dd96a3663e8b7ff8e (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
/*
 * Copyright (C) 2013 Reimar Döffinger <Reimar.Doeffinger@gmx.de>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#include <stdint.h>
#include "mem.h"
#include "intreadwrite.h"
#include "murmur3.h"

typedef struct AVMurMur3 {
    uint64_t h1, h2;
    uint8_t state[16];
    int state_pos;
    uint64_t len;
} AVMurMur3;

AVMurMur3 *av_murmur3_alloc(void)
{
    return av_mallocz(sizeof(AVMurMur3));
}

void av_murmur3_init_seeded(AVMurMur3 *c, uint64_t seed)
{
    memset(c, 0, sizeof(*c));
    c->h1 = c->h2 = seed;
}

void av_murmur3_init(AVMurMur3 *c)
{
    // arbitrary random number as seed
    av_murmur3_init_seeded(c, 0x725acc55daddca55);
}

static const uint64_t c1 = UINT64_C(0x87c37b91114253d5);
static const uint64_t c2 = UINT64_C(0x4cf5ad432745937f);

#define ROT(a, b) ((a << b) | (a >> (64 - b)))

static uint64_t inline get_k1(const uint8_t *src)
{
    uint64_t k = AV_RL64(src);
    k *= c1;
    k = ROT(k, 31);
    k *= c2;
    return k;
}

static uint64_t inline get_k2(const uint8_t *src)
{
    uint64_t k = AV_RL64(src + 8);
    k *= c2;
    k = ROT(k, 33);
    k *= c1;
    return k;
}

static uint64_t inline update_h1(uint64_t k, uint64_t h1, uint64_t h2)
{
    k ^= h1;
    k = ROT(k, 27);
    k += h2;
    k *= 5;
    k += 0x52dce729;
    return k;
}

static uint64_t inline update_h2(uint64_t k, uint64_t h1, uint64_t h2)
{
    k ^= h2;
    k = ROT(k, 31);
    k += h1;
    k *= 5;
    k += 0x38495ab5;
    return k;
}

void av_murmur3_update(AVMurMur3 *c, const uint8_t *src, int len)
{
    const uint8_t *end;
    uint64_t h1 = c->h1, h2 = c->h2;
    uint64_t k1, k2;
    if (len <= 0) return;
    c->len += len;
    if (c->state_pos > 0) {
        while (c->state_pos < 16) {
            c->state[c->state_pos++] = *src++;
            if (--len <= 0) return;
        }
        c->state_pos = 0;
        k1 = get_k1(c->state);
        k2 = get_k2(c->state);
        h1 = update_h1(k1, h1, h2);
        h2 = update_h2(k2, h1, h2);
    }

    end = src + (len & ~15);
    while (src < end) {
        // These could be done sequentially instead
        // of interleaved, but like this is over 10% faster
        k1 = get_k1(src);
        k2 = get_k2(src);
        h1 = update_h1(k1, h1, h2);
        h2 = update_h2(k2, h1, h2);
        src += 16;
    }
    c->h1 = h1;
    c->h2 = h2;

    len &= 15;
    if (len > 0) {
        memcpy(c->state, src, len);
        c->state_pos = len;
    }
}

static inline uint64_t fmix(uint64_t k)
{
    k ^= k >> 33;
    k *= UINT64_C(0xff51afd7ed558ccd);
    k ^= k >> 33;
    k *= UINT64_C(0xc4ceb9fe1a85ec53);
    k ^= k >> 33;
    return k;
}

void av_murmur3_final(AVMurMur3 *c, uint8_t dst[16])
{
    uint64_t h1 = c->h1, h2 = c->h2;
    memset(c->state + c->state_pos, 0, sizeof(c->state) - c->state_pos);
    h1 ^= get_k1(c->state) ^ c->len;
    h2 ^= get_k2(c->state) ^ c->len;
    h1 += h2;
    h2 += h1;
    h1 = fmix(h1);
    h2 = fmix(h2);
    h1 += h2;
    h2 += h1;
    AV_WL64(dst, h1);
    AV_WL64(dst + 8, h2);
}

#ifdef TEST
int main(void)
{
    int i;
    uint8_t hash_result[16] = {0};
    AVMurMur3 *ctx = av_murmur3_alloc();
#if 1
    uint8_t in[256] = {0};
    uint8_t *hashes = av_mallocz(256 * 16);
    for (i = 0; i < 256; i++)
    {
        in[i] = i;
        av_murmur3_init_seeded(ctx, 256 - i);
        // Note: this actually tests hashing 0 bytes
        av_murmur3_update(ctx, in, i);
        av_murmur3_final(ctx, hashes + 16 * i);
    }
    av_murmur3_init_seeded(ctx, 0);
    av_murmur3_update(ctx, hashes, 256 * 16);
    av_murmur3_final(ctx, hash_result);
    av_free(hashes);
    av_freep(&ctx);
    printf("result: 0x%"PRIx64" 0x%"PRIx64"\n", AV_RL64(hash_result), AV_RL64(hash_result + 8));
    // official reference value is 32 bit
    return AV_RL32(hash_result) != 0x6384ba69;
#else
    uint8_t *in = av_mallocz(512*1024);
    av_murmur3_init(ctx);
    for (i = 0; i < 40*1024; i++)
        av_murmur3_update(ctx, in, 512*1024);
    av_murmur3_final(ctx, hash_result);
    av_free(in);
    return hash_result[0];
#endif
}
#endif