152 lines
4.8 KiB
C
152 lines
4.8 KiB
C
/*
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* copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "common.h"
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#include "crc.h"
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#ifdef CONFIG_HARDCODED_TABLES
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#include "crc_data.h"
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#else
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static struct {
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uint8_t le;
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uint8_t bits;
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uint32_t poly;
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} av_crc_table_params[AV_CRC_MAX] = {
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[AV_CRC_8_ATM] = { 0, 8, 0x07 },
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[AV_CRC_16_ANSI] = { 0, 16, 0x8005 },
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[AV_CRC_16_CCITT] = { 0, 16, 0x1021 },
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[AV_CRC_32_IEEE] = { 0, 32, 0x04C11DB7 },
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[AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
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};
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static AVCRC av_crc_table[AV_CRC_MAX][257];
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#endif
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/**
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* Inits a crc table.
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* @param ctx must be an array of sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
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* @param cts_size size of ctx in bytes
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* @param le if 1, lowest bit represents coefficient for highest exponent
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* of corresponding polynomial (both for poly and actual CRC).
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* If 0, you must swap the crc parameter and the result of av_crc
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* if you need the standard representation (can be simplified in
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* most cases to e.g. bswap16):
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* bswap_32(crc << (32-bits))
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* @param bits number of bits for the CRC
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* @param poly generator polynomial without the x**bits coefficient, in the
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* representation as specified by le
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* @return <0 on failure
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*/
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int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
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int i, j;
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uint32_t c;
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if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
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return -1;
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if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
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return -1;
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for (i = 0; i < 256; i++) {
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if (le) {
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for (c = i, j = 0; j < 8; j++)
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c = (c>>1)^(poly & (-(c&1)));
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ctx[i] = c;
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} else {
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for (c = i << 24, j = 0; j < 8; j++)
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c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
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ctx[i] = bswap_32(c);
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}
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}
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ctx[256]=1;
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#ifndef CONFIG_SMALL
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if(ctx_size >= sizeof(AVCRC)*1024)
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for (i = 0; i < 256; i++)
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for(j=0; j<3; j++)
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ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
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#endif
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return 0;
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}
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/**
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* Get an initialized standard CRC table.
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* @param crc_id ID of a standard CRC
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* @return a pointer to the CRC table or NULL on failure
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*/
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const AVCRC *av_crc_get_table(AVCRCId crc_id){
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#ifndef CONFIG_HARDCODED_TABLES
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if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id])-1])
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if (av_crc_init(av_crc_table[crc_id],
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av_crc_table_params[crc_id].le,
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av_crc_table_params[crc_id].bits,
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av_crc_table_params[crc_id].poly,
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sizeof(av_crc_table[crc_id])) < 0)
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return NULL;
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#endif
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return av_crc_table[crc_id];
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}
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/**
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* Calculate the CRC of a block
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* @param crc CRC of previous blocks if any or initial value for CRC.
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* @return CRC updated with the data from the given block
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*
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* @see av_crc_init() "le" parameter
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*/
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uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
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const uint8_t *end= buffer+length;
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#ifndef CONFIG_SMALL
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if(!ctx[256])
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while(buffer<end-3){
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crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
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crc = ctx[3*256 + ( crc &0xFF)]
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^ctx[2*256 + ((crc>>8 )&0xFF)]
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^ctx[1*256 + ((crc>>16)&0xFF)]
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^ctx[0*256 + ((crc>>24) )];
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}
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#endif
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while(buffer<end)
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crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
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return crc;
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}
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#ifdef TEST
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#undef printf
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int main(void){
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uint8_t buf[1999];
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int i;
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int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},
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{AV_CRC_32_IEEE , 0x04C11DB7, 0xC0F5BAE0},
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{AV_CRC_16_ANSI , 0x8005, 0x1FBB },
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{AV_CRC_8_ATM , 0x07, 0xE3 },};
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const AVCRC *ctx;
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for(i=0; i<sizeof(buf); i++)
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buf[i]= i+i*i;
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for(i=0; i<4; i++){
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ctx = av_crc_get_table(p[i][0]);
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printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
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}
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return 0;
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}
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#endif
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