44719ffaee3554263184c90710dd726bae9adcd1
[libav.git] / libavutil / crc.c
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;
33 } av_crc_table_params[AV_CRC_MAX] = {
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 };
40 static AVCRC av_crc_table[AV_CRC_MAX][257];
41 #endif
42
43 /**
44 * Initialize a CRC table.
45 * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
46 * @param le If 1, the lowest bit represents the coefficient for the highest
47 * exponent of the corresponding polynomial (both for poly and
48 * actual CRC).
49 * If 0, you must swap the CRC parameter and the result of av_crc
50 * if you need the standard representation (can be simplified in
51 * most cases to e.g. bswap16):
52 * av_bswap32(crc << (32-bits))
53 * @param bits number of bits for the CRC
54 * @param poly generator polynomial without the x**bits coefficient, in the
55 * representation as specified by le
56 * @param ctx_size size of ctx in bytes
57 * @return <0 on failure
58 */
59 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
60 unsigned i, j;
61 uint32_t c;
62
63 if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
64 return -1;
65 if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
66 return -1;
67
68 for (i = 0; i < 256; i++) {
69 if (le) {
70 for (c = i, j = 0; j < 8; j++)
71 c = (c>>1)^(poly & (-(c&1)));
72 ctx[i] = c;
73 } else {
74 for (c = i << 24, j = 0; j < 8; j++)
75 c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
76 ctx[i] = av_bswap32(c);
77 }
78 }
79 ctx[256]=1;
80 #if !CONFIG_SMALL
81 if(ctx_size >= sizeof(AVCRC)*1024)
82 for (i = 0; i < 256; i++)
83 for(j=0; j<3; j++)
84 ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
85 #endif
86
87 return 0;
88 }
89
90 /**
91 * Get an initialized standard CRC table.
92 * @param crc_id ID of a standard CRC
93 * @return a pointer to the CRC table or NULL on failure
94 */
95 const AVCRC *av_crc_get_table(AVCRCId crc_id){
96 #if !CONFIG_HARDCODED_TABLES
97 if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1])
98 if (av_crc_init(av_crc_table[crc_id],
99 av_crc_table_params[crc_id].le,
100 av_crc_table_params[crc_id].bits,
101 av_crc_table_params[crc_id].poly,
102 sizeof(av_crc_table[crc_id])) < 0)
103 return NULL;
104 #endif
105 return av_crc_table[crc_id];
106 }
107
108 /**
109 * Calculate the CRC of a block.
110 * @param crc CRC of previous blocks if any or initial value for CRC
111 * @return CRC updated with the data from the given block
112 *
113 * @see av_crc_init() "le" parameter
114 */
115 uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
116 const uint8_t *end= buffer+length;
117
118 #if !CONFIG_SMALL
119 if(!ctx[256]) {
120 while(((intptr_t) buffer & 3) && buffer < end)
121 crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
122
123 while(buffer<end-3){
124 crc ^= av_le2ne32(*(const uint32_t*)buffer); buffer+=4;
125 crc = ctx[3*256 + ( crc &0xFF)]
126 ^ctx[2*256 + ((crc>>8 )&0xFF)]
127 ^ctx[1*256 + ((crc>>16)&0xFF)]
128 ^ctx[0*256 + ((crc>>24) )];
129 }
130 }
131 #endif
132 while(buffer<end)
133 crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
134
135 return crc;
136 }
137
138 #ifdef TEST
139 #undef printf
140 int main(void){
141 uint8_t buf[1999];
142 int i;
143 int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
144 {AV_CRC_32_IEEE , 0x04C11DB7, 0xC0F5BAE0},
145 {AV_CRC_16_ANSI , 0x8005, 0x1FBB },
146 {AV_CRC_8_ATM , 0x07, 0xE3 },};
147 const AVCRC *ctx;
148
149 for(i=0; i<sizeof(buf); i++)
150 buf[i]= i+i*i;
151
152 for(i=0; i<4; i++){
153 ctx = av_crc_get_table(p[i][0]);
154 printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
155 }
156 return 0;
157 }
158 #endif