2 * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
4 * This file is part of FFmpeg.
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.
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.
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
25 #ifdef CONFIG_HARDCODED_TABLES
32 } av_crc_table_params[AV_CRC_MAX] = {
33 [AV_CRC_8_ATM] = { 0, 8, 0x07 },
34 [AV_CRC_16_ANSI] = { 0, 16, 0x8005 },
35 [AV_CRC_16_CCITT] = { 0, 16, 0x1021 },
36 [AV_CRC_32_IEEE] = { 0, 32, 0x04C11DB7 },
37 [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
39 static AVCRC av_crc_table[AV_CRC_MAX][257];
44 * @param ctx must be an array of sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
45 * @param cts_size size of ctx in bytes
46 * @param le if 1, lowest bit represents coefficient for highest exponent
47 * of corresponding polynomial (both for poly and actual CRC).
48 * If 0, you must swap the crc parameter and the result of av_crc
49 * if you need the standard representation (can be simplified in
50 * most cases to e.g. bswap16):
51 * bswap_32(crc << (32-bits))
52 * @param bits number of bits for the CRC
53 * @param poly generator polynomial without the x**bits coefficient, in the
54 * representation as specified by le
55 * @return <0 on failure
57 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
61 if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
63 if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
66 for (i = 0; i < 256; i++) {
68 for (c = i, j = 0; j < 8; j++)
69 c = (c>>1)^(poly & (-(c&1)));
72 for (c = i << 24, j = 0; j < 8; j++)
73 c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
79 if(ctx_size >= sizeof(AVCRC)*1024)
80 for (i = 0; i < 256; i++)
82 ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
89 * Get an initialized standard CRC table.
90 * @param crc_id ID of a standard CRC
91 * @return a pointer to the CRC table or NULL on failure
93 const AVCRC *av_crc_get_table(AVCRCId crc_id){
94 #ifndef CONFIG_HARDCODED_TABLES
95 if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1])
96 if (av_crc_init(av_crc_table[crc_id],
97 av_crc_table_params[crc_id].le,
98 av_crc_table_params[crc_id].bits,
99 av_crc_table_params[crc_id].poly,
100 sizeof(av_crc_table[crc_id])) < 0)
103 return av_crc_table[crc_id];
107 * Calculate the CRC of a block
108 * @param crc CRC of previous blocks if any or initial value for CRC.
109 * @return CRC updated with the data from the given block
111 * @see av_crc_init() "le" parameter
113 uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
114 const uint8_t *end= buffer+length;
119 crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
120 crc = ctx[3*256 + ( crc &0xFF)]
121 ^ctx[2*256 + ((crc>>8 )&0xFF)]
122 ^ctx[1*256 + ((crc>>16)&0xFF)]
123 ^ctx[0*256 + ((crc>>24) )];
127 crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
137 int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
138 {AV_CRC_32_IEEE , 0x04C11DB7, 0xC0F5BAE0},
139 {AV_CRC_16_ANSI , 0x8005, 0x1FBB },
140 {AV_CRC_8_ATM , 0x07, 0xE3 },};
143 for(i=0; i<sizeof(buf); i++)
147 ctx = av_crc_get_table(p[i][0]);
148 printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));