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ffmpeg / libavutil / crc.c @ a08d38ee

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#include "common.h"
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#include "crc.h"
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AVCRC *av_crcEDB88320;
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AVCRC *av_crc04C11DB7;
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AVCRC *av_crc8005    ;
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AVCRC *av_crc07      ;
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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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 * @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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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(*(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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main(){
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    uint8_t buf[1999];
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    int i;
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    int p[4][4]={{1, 32, 0xedb88320L, 0x3D5CDD04},
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                 {0, 32, 0x04c11db7L, 0xC0F5BAE0},
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                 {0, 16, 0x8005     , 0x1FBB    },
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                 {0,  8, 0x07       , 0xE3      },};
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    AVCRC ctx[1 ? 1024:257];
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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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        av_crc_init(ctx, p[i][0], p[i][1], p[i][2], sizeof(ctx));
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        printf("crc %08X =%X\n", p[i][2], av_crc(ctx, 0, buf, sizeof(buf)));
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    }
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}
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#endif