1/*
2 * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
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 "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
29static 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};
40static AVCRC av_crc_table[AV_CRC_MAX][257];
41#endif
42
43/**
44 * Initializes a CRC table.
45 * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
46 * @param cts_size size of ctx in bytes
47 * @param le If 1, the lowest bit represents the coefficient for the highest
48 *           exponent of the corresponding polynomial (both for poly and
49 *           actual CRC).
50 *           If 0, you must swap the CRC parameter and the result of av_crc
51 *           if you need the standard representation (can be simplified in
52 *           most cases to e.g. bswap16):
53 *           bswap_32(crc << (32-bits))
54 * @param bits number of bits for the CRC
55 * @param poly generator polynomial without the x**bits coefficient, in the
56 *             representation as specified by le
57 * @return <0 on failure
58 */
59int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
60    int 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] = bswap_32(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 * Gets 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 */
95const 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 * Calculates 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 */
115uint32_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 ^= le2me_32(*(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
140int 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
159