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lfg.c
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1 /*
2  * Lagged Fibonacci PRNG
3  * Copyright (c) 2008 Michael Niedermayer
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #include <inttypes.h>
23 #include <limits.h>
24 #include <math.h>
25 #include "lfg.h"
26 #include "crc.h"
27 #include "md5.h"
28 #include "error.h"
29 #include "intreadwrite.h"
30 #include "attributes.h"
31 
32 av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
33 {
34  uint8_t tmp[16] = { 0 };
35  int i;
36 
37  for (i = 8; i < 64; i += 4) {
38  AV_WL32(tmp, seed);
39  tmp[4] = i;
40  av_md5_sum(tmp, tmp, 16);
41  c->state[i ] = AV_RL32(tmp);
42  c->state[i + 1] = AV_RL32(tmp + 4);
43  c->state[i + 2] = AV_RL32(tmp + 8);
44  c->state[i + 3] = AV_RL32(tmp + 12);
45  }
46  c->index = 0;
47 }
48 
49 void av_bmg_get(AVLFG *lfg, double out[2])
50 {
51  double x1, x2, w;
52 
53  do {
54  x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
55  x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
56  w = x1 * x1 + x2 * x2;
57  } while (w >= 1.0);
58 
59  w = sqrt((-2.0 * log(w)) / w);
60  out[0] = x1 * w;
61  out[1] = x2 * w;
62 }
63 
64 int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length) {
65  unsigned int beg, end, segm;
66  const AVCRC *avcrc;
67  uint32_t crc = 1;
68 
69  /* avoid integer overflow in the loop below. */
70  if (length > (UINT_MAX / 128U)) return AVERROR(EINVAL);
71 
72  c->index = 0;
73  avcrc = av_crc_get_table(AV_CRC_32_IEEE); /* This can't fail. It's a well-defined table in crc.c */
74 
75  /* across 64 segments of the incoming data,
76  * do a running crc of each segment and store the crc as the state for that slot.
77  * this works even if the length of the segment is 0 bytes. */
78  beg = 0;
79  for (segm = 0;segm < 64;segm++) {
80  end = (((segm + 1) * length) / 64);
81  crc = av_crc(avcrc, crc, data + beg, end - beg);
82  c->state[segm] = (unsigned int)crc;
83  beg = end;
84  }
85 
86  return 0;
87 }
Definition: lfg.h:27
int index
Definition: lfg.h:29
ptrdiff_t const GLvoid * data
Definition: opengl_enc.c:101
uint64_t i
Definition: intfloat.h:33
Macro definitions for various function/variable attributes.
uint8_t
#define av_cold
Definition: attributes.h:82
static av_cold int end(AVCodecContext *avctx)
Definition: avrndec.c:90
Public header for CRC hash function implementation.
void av_md5_sum(uint8_t *dst, const uint8_t *src, const int len)
Hash an array of data.
Definition: md5.c:207
void av_bmg_get(AVLFG *lfg, double out[2])
Get the next two numbers generated by a Box-Muller Gaussian generator using the random numbers issued...
Definition: lfg.c:49
#define U(x)
Definition: vp56_arith.h:37
error code definitions
#define AVERROR(e)
Definition: error.h:43
GLsizei GLsizei * length
Definition: opengl_enc.c:115
uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length)
Calculate the CRC of a block.
Definition: crc.c:357
int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length)
Seed the state of the ALFG using binary data.
Definition: lfg.c:64
static unsigned int seed
Definition: videogen.c:78
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:47
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:32
const AVCRC * av_crc_get_table(AVCRCId crc_id)
Get an initialized standard CRC table.
Definition: crc.c:343
int
unsigned int state[64]
Definition: lfg.h:28
static double c[64]
FILE * out
Definition: movenc.c:54
Public header for MD5 hash function implementation.
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_RL32
Definition: bytestream.h:87
uint32_t AVCRC
Definition: crc.h:47
#define AV_WL32(p, v)
Definition: intreadwrite.h:426
static uint8_t tmp[11]
Definition: aes_ctr.c:26