FFmpeg
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 }
AVERROR
Filter the word “frame” indicates either a video frame or a group of audio as stored in an AVFrame structure Format for each input and each output the list of supported formats For video that means pixel format For audio that means channel sample they are references to shared objects When the negotiation mechanism computes the intersection of the formats supported at each end of a all references to both lists are replaced with a reference to the intersection And when a single format is eventually chosen for a link amongst the remaining all references to the list are updated That means that if a filter requires that its input and output have the same format amongst a supported all it has to do is use a reference to the same list of formats query_formats can leave some formats unset and return AVERROR(EAGAIN) to cause the negotiation mechanism toagain later. That can be used by filters with complex requirements to use the format negotiated on one link to set the formats supported on another. Frame references ownership and permissions
AV_WL32
#define AV_WL32(p, v)
Definition: intreadwrite.h:426
out
FILE * out
Definition: movenc.c:54
av_lfg_init
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:32
AVCRC
uint32_t AVCRC
Definition: crc.h:46
tmp
static uint8_t tmp[11]
Definition: aes_ctr.c:26
w
uint8_t w
Definition: llviddspenc.c:38
data
const char data[16]
Definition: mxf.c:143
crc.h
U
#define U(x)
Definition: vp56_arith.h:37
av_cold
#define av_cold
Definition: attributes.h:90
intreadwrite.h
av_lfg_get
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:53
lfg.h
av_bmg_get
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
limits.h
seed
static unsigned int seed
Definition: videogen.c:78
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
error.h
AVLFG
Context structure for the Lagged Fibonacci PRNG.
Definition: lfg.h:33
av_md5_sum
void av_md5_sum(uint8_t *dst, const uint8_t *src, size_t len)
Hash an array of data.
Definition: md5.c:201
av_crc_get_table
const AVCRC * av_crc_get_table(AVCRCId crc_id)
Get an initialized standard CRC table.
Definition: crc.c:374
attributes.h
av_lfg_init_from_data
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
i
#define i(width, name, range_min, range_max)
Definition: cbs_h2645.c:271
md5.h
AV_CRC_32_IEEE
@ AV_CRC_32_IEEE
Definition: crc.h:52
AV_RL32
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_RL32
Definition: bytestream.h:92
av_crc
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:392
int
int
Definition: ffmpeg_filter.c:156