FFmpeg
trasher.c
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1 /*
2  * Copyright (c) 2007 Michael Niedermayer
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 <stdio.h>
22 #include <stdlib.h>
23 #include <inttypes.h>
24 #include <errno.h>
25 #include <string.h>
26 
27 static uint32_t state;
28 static uint32_t ran(void)
29 {
30  return state = state * 1664525 + 1013904223;
31 }
32 
33 static void checked_seek(FILE *stream, int64_t offset, int whence)
34 {
35  offset = fseek(stream, offset, whence);
36  if (offset < 0) {
37  fprintf(stderr, "seek failed\n");
38  exit(1);
39  }
40 }
41 
42 int main(int argc, char **argv)
43 {
44  FILE *f;
45  int count, maxburst, length;
46 
47  if (argc < 5) {
48  printf("USAGE: trasher <filename> <count> <maxburst> <seed>\n");
49  return 1;
50  }
51 
52  f = fopen(argv[1], "rb+");
53  if (!f) {
54  perror(argv[1]);
55  return 2;
56  }
57  count = atoi(argv[2]);
58  maxburst = atoi(argv[3]);
59  state = atoi(argv[4]);
60 
61  checked_seek(f, 0, SEEK_END);
62  length = ftell(f);
63  checked_seek(f, 0, SEEK_SET);
64 
65  while (count--) {
66  int burst = 1 + ran() * (uint64_t) (abs(maxburst) - 1) / UINT32_MAX;
67  int pos = ran() * (uint64_t) length / UINT32_MAX;
68  checked_seek(f, pos, SEEK_SET);
69 
70  if (maxburst < 0)
71  burst = -maxburst;
72 
73  if (pos + burst > length)
74  continue;
75 
76  while (burst--) {
77  int val = ran() * 256ULL / UINT32_MAX;
78 
79  if (maxburst < 0)
80  val = 0;
81 
82  fwrite(&val, 1, 1, f);
83  }
84  }
85 
86  return 0;
87 }
it s the only field you need to keep assuming you have a context There is some magic you don t need to care about around this just let it vf offset
#define f(width, name)
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int main(int argc, char **argv)
Definition: trasher.c:42
unsigned int pos
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GLsizei count
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static uint32_t ran(void)
Definition: trasher.c:28
#define abs(x)
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Definition: trasher.c:27
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static void checked_seek(FILE *stream, int64_t offset, int whence)
Definition: trasher.c:33
static double val(void *priv, double ch)
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