crc.c
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1 /*
2  * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
3  *
4  * This file is part of Libav.
5  *
6  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 #include "config.h"
22 #include "common.h"
23 #include "bswap.h"
24 #include "crc.h"
25 
26 #if CONFIG_HARDCODED_TABLES
27 #include "crc_data.h"
28 #else
29 static struct {
30  uint8_t le;
31  uint8_t bits;
32  uint32_t poly;
34  [AV_CRC_8_ATM] = { 0, 8, 0x07 },
35  [AV_CRC_16_ANSI] = { 0, 16, 0x8005 },
36  [AV_CRC_16_CCITT] = { 0, 16, 0x1021 },
37  [AV_CRC_32_IEEE] = { 0, 32, 0x04C11DB7 },
38  [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
39 };
41 #endif
42 
59 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
60 {
61  unsigned i, j;
62  uint32_t c;
63 
64  if (bits < 8 || bits > 32 || poly >= (1LL << bits))
65  return -1;
66  if (ctx_size != sizeof(AVCRC) * 257 && ctx_size != sizeof(AVCRC) * 1024)
67  return -1;
68 
69  for (i = 0; i < 256; i++) {
70  if (le) {
71  for (c = i, j = 0; j < 8; j++)
72  c = (c >> 1) ^ (poly & (-(c & 1)));
73  ctx[i] = c;
74  } else {
75  for (c = i << 24, j = 0; j < 8; j++)
76  c = (c << 1) ^ ((poly << (32 - bits)) & (((int32_t) c) >> 31));
77  ctx[i] = av_bswap32(c);
78  }
79  }
80  ctx[256] = 1;
81 #if !CONFIG_SMALL
82  if (ctx_size >= sizeof(AVCRC) * 1024)
83  for (i = 0; i < 256; i++)
84  for (j = 0; j < 3; j++)
85  ctx[256 *(j + 1) + i] =
86  (ctx[256 * j + i] >> 8) ^ ctx[ctx[256 * j + i] & 0xFF];
87 #endif
88 
89  return 0;
90 }
91 
98 {
99 #if !CONFIG_HARDCODED_TABLES
100  if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id]) - 1])
101  if (av_crc_init(av_crc_table[crc_id],
102  av_crc_table_params[crc_id].le,
103  av_crc_table_params[crc_id].bits,
104  av_crc_table_params[crc_id].poly,
105  sizeof(av_crc_table[crc_id])) < 0)
106  return NULL;
107 #endif
108  return av_crc_table[crc_id];
109 }
110 
118 uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
119  const uint8_t *buffer, size_t length)
120 {
121  const uint8_t *end = buffer + length;
122 
123 #if !CONFIG_SMALL
124  if (!ctx[256]) {
125  while (((intptr_t) buffer & 3) && buffer < end)
126  crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
127 
128  while (buffer < end - 3) {
129  crc ^= av_le2ne32(*(const uint32_t *) buffer); buffer += 4;
130  crc = ctx[3 * 256 + ( crc & 0xFF)] ^
131  ctx[2 * 256 + ((crc >> 8 ) & 0xFF)] ^
132  ctx[1 * 256 + ((crc >> 16) & 0xFF)] ^
133  ctx[0 * 256 + ((crc >> 24) )];
134  }
135  }
136 #endif
137  while (buffer < end)
138  crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
139 
140  return crc;
141 }
142 
143 #ifdef TEST
144 #undef printf
145 int main(void)
146 {
147  uint8_t buf[1999];
148  int i;
149  int p[4][3] = { { AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04 },
150  { AV_CRC_32_IEEE , 0x04C11DB7, 0xC0F5BAE0 },
151  { AV_CRC_16_ANSI , 0x8005 , 0x1FBB },
152  { AV_CRC_8_ATM , 0x07 , 0xE3 }
153  };
154  const AVCRC *ctx;
155 
156  for (i = 0; i < sizeof(buf); i++)
157  buf[i] = i + i * i;
158 
159  for (i = 0; i < 4; i++) {
160  ctx = av_crc_get_table(p[i][0]);
161  printf("crc %08X = %X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
162  }
163  return 0;
164 }
165 #endif