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 "bswap.h"
23#include "crc.h"
24
25#if CONFIG_HARDCODED_TABLES
26#include "crc_data.h"
27#else
28static struct {
29    uint8_t  le;
30    uint8_t  bits;
31    uint32_t poly;
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 },
38};
39static AVCRC av_crc_table[AV_CRC_MAX][257];
40#endif
41
42/**
43 * Initializes a CRC table.
44 * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
45 * @param cts_size size of ctx in bytes
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 *           bswap_32(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 * @return <0 on failure
57 */
58int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
59    int i, j;
60    uint32_t c;
61
62    if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
63        return -1;
64    if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
65        return -1;
66
67    for (i = 0; i < 256; i++) {
68        if (le) {
69            for (c = i, j = 0; j < 8; j++)
70                c = (c>>1)^(poly & (-(c&1)));
71            ctx[i] = c;
72        } else {
73            for (c = i << 24, j = 0; j < 8; j++)
74                c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
75            ctx[i] = bswap_32(c);
76        }
77    }
78    ctx[256]=1;
79#if !CONFIG_SMALL
80    if(ctx_size >= sizeof(AVCRC)*1024)
81        for (i = 0; i < 256; i++)
82            for(j=0; j<3; j++)
83                ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
84#endif
85
86    return 0;
87}
88
89/**
90 * Gets an initialized standard CRC table.
91 * @param crc_id ID of a standard CRC
92 * @return a pointer to the CRC table or NULL on failure
93 */
94const AVCRC *av_crc_get_table(AVCRCId crc_id){
95#if !CONFIG_HARDCODED_TABLES
96    if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1])
97        if (av_crc_init(av_crc_table[crc_id],
98                        av_crc_table_params[crc_id].le,
99                        av_crc_table_params[crc_id].bits,
100                        av_crc_table_params[crc_id].poly,
101                        sizeof(av_crc_table[crc_id])) < 0)
102            return NULL;
103#endif
104    return av_crc_table[crc_id];
105}
106
107/**
108 * Calculates the CRC of a block.
109 * @param crc CRC of previous blocks if any or initial value for CRC
110 * @return CRC updated with the data from the given block
111 *
112 * @see av_crc_init() "le" parameter
113 */
114uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
115    const uint8_t *end= buffer+length;
116
117#if !CONFIG_SMALL
118    if(!ctx[256])
119        while(buffer<end-3){
120            crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
121            crc =  ctx[3*256 + ( crc     &0xFF)]
122                  ^ctx[2*256 + ((crc>>8 )&0xFF)]
123                  ^ctx[1*256 + ((crc>>16)&0xFF)]
124                  ^ctx[0*256 + ((crc>>24)     )];
125        }
126#endif
127    while(buffer<end)
128        crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
129
130    return crc;
131}
132
133#ifdef TEST
134#undef printf
135int main(void){
136    uint8_t buf[1999];
137    int i;
138    int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
139                 {AV_CRC_32_IEEE   , 0x04C11DB7, 0xC0F5BAE0},
140                 {AV_CRC_16_ANSI   , 0x8005,     0x1FBB    },
141                 {AV_CRC_8_ATM     , 0x07,       0xE3      },};
142    const AVCRC *ctx;
143
144    for(i=0; i<sizeof(buf); i++)
145        buf[i]= i+i*i;
146
147    for(i=0; i<4; i++){
148        ctx = av_crc_get_table(p[i][0]);
149        printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
150    }
151    return 0;
152}
153#endif
154