libavutil/murmur3.c

   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 #include <stddef.h>
  22 #include <stdint.h>
  23 #include <string.h>
  24 #include "mem.h"
  25 #include "intreadwrite.h"
  26 #include "murmur3.h"
  27
  28 typedef struct AVMurMur3 {
  29     uint64_t h1, h2;
  30     uint8_t state[16];
  31     int state_pos;
  32     uint64_t len;
  33 } AVMurMur3;
  34
  35 AVMurMur3 *av_murmur3_alloc(void)
  36 {
  37     return av_mallocz(sizeof(AVMurMur3));
  38 }
  39
  40 void av_murmur3_init_seeded(AVMurMur3 *c, uint64_t seed)
  41 {
  42     memset(c, 0, sizeof(*c));
  43     c->h1 = c->h2 = seed;
  44 }
  45
  46 void av_murmur3_init(AVMurMur3 *c)
  47 {
  48     // arbitrary random number as seed
  49     av_murmur3_init_seeded(c, 0x725acc55daddca55);
  50 }
  51
  52 static const uint64_t c1 = UINT64_C(0x87c37b91114253d5);
  53 static const uint64_t c2 = UINT64_C(0x4cf5ad432745937f);
  54
  55 #define ROT(a, b) (((a) << (b)) | ((a) >> (64 - (b))))
  56
  57 static uint64_t inline get_k1(const uint8_t *src)
  58 {
  59     uint64_t k = AV_RL64(src);
  60     k *= c1;
  61     k = ROT(k, 31);
  62     k *= c2;
  63     return k;
  64 }
  65
  66 static inline uint64_t get_k2(const uint8_t *src)
  67 {
  68     uint64_t k = AV_RL64(src + 8);
  69     k *= c2;
  70     k = ROT(k, 33);
  71     k *= c1;
  72     return k;
  73 }
  74
  75 static inline uint64_t update_h1(uint64_t k, uint64_t h1, uint64_t h2)
  76 {
  77     k ^= h1;
  78     k = ROT(k, 27);
  79     k += h2;
  80     k *= 5;
  81     k += 0x52dce729;
  82     return k;
  83 }
  84
  85 static inline uint64_t update_h2(uint64_t k, uint64_t h1, uint64_t h2)
  86 {
  87     k ^= h2;
  88     k = ROT(k, 31);
  89     k += h1;
  90     k *= 5;
  91     k += 0x38495ab5;
  92     return k;
  93 }
  94
  95 void av_murmur3_update(AVMurMur3 *c, const uint8_t *src, size_t len)
  96 {
  97     const uint8_t *end;
  98     uint64_t h1 = c->h1, h2 = c->h2;
  99     uint64_t k1, k2;
 100     if (len <= 0) return;
 101     c->len += len;
 102     if (c->state_pos > 0) {
 103         while (c->state_pos < 16) {
 104             c->state[c->state_pos++] = *src++;
 105             if (--len <= 0) return;
 106         }
 107         c->state_pos = 0;
 108         k1 = get_k1(c->state);
 109         k2 = get_k2(c->state);
 110         h1 = update_h1(k1, h1, h2);
 111         h2 = update_h2(k2, h1, h2);
 112     }
 113
 114     end = src + (len & ~15);
 115     while (src < end) {
 116         // These could be done sequentially instead
 117         // of interleaved, but like this is over 10% faster
 118         k1 = get_k1(src);
 119         k2 = get_k2(src);
 120         h1 = update_h1(k1, h1, h2);
 121         h2 = update_h2(k2, h1, h2);
 122         src += 16;
 123     }
 124     c->h1 = h1;
 125     c->h2 = h2;
 126
 127     len &= 15;
 128     if (len > 0) {
 129         memcpy(c->state, src, len);
 130         c->state_pos = len;
 131     }
 132 }
 133
 134 static inline uint64_t fmix(uint64_t k)
 135 {
 136     k ^= k >> 33;
 137     k *= UINT64_C(0xff51afd7ed558ccd);
 138     k ^= k >> 33;
 139     k *= UINT64_C(0xc4ceb9fe1a85ec53);
 140     k ^= k >> 33;
 141     return k;
 142 }
 143
 144 void av_murmur3_final(AVMurMur3 *c, uint8_t dst[16])
 145 {
 146     uint64_t h1 = c->h1, h2 = c->h2;
 147     memset(c->state + c->state_pos, 0, sizeof(c->state) - c->state_pos);
 148     h1 ^= get_k1(c->state) ^ c->len;
 149     h2 ^= get_k2(c->state) ^ c->len;
 150     h1 += h2;
 151     h2 += h1;
 152     h1 = fmix(h1);
 153     h2 = fmix(h2);
 154     h1 += h2;
 155     h2 += h1;
 156     AV_WL64(dst, h1);
 157     AV_WL64(dst + 8, h2);
 158 }