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crc.c 2.18 KiB
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  • #include "common.h"
    #include "crc.h"
    
    AVCRC *av_crcEDB88320;
    AVCRC *av_crc04C11DB7;
    AVCRC *av_crc8005    ;
    AVCRC *av_crc07      ;
    
    /**
     * Inits a crc table.
     * @param ctx must be an array of sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
     * @param cts_size size of ctx in bytes
     * @return <0 on failure
     */
    int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size){
        int i, j;
        uint32_t c;
    
        if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
            return -1;
        if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
            return -1;
    
        for (i = 0; i < 256; i++) {
            if (le) {
                for (c = i, j = 0; j < 8; j++)
                    c = (c>>1)^(poly & (-(c&1)));
                ctx[i] = c;
            } else {
                for (c = i << 24, j = 0; j < 8; j++)
                    c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
                ctx[i] = bswap_32(c);
            }
        }
        ctx[256]=1;
        if(ctx_size >= sizeof(AVCRC)*1024)
            for (i = 0; i < 256; i++)
                for(j=0; j<3; j++)
                    ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
    
        return 0;
    }
    
    uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){
        const uint8_t *end= buffer+length;
    
        if(!ctx[256])
            while(buffer<end-3){
                crc ^= le2me_32(*(uint32_t*)buffer); buffer+=4;
                crc =  ctx[3*256 + ( crc     &0xFF)]
                      ^ctx[2*256 + ((crc>>8 )&0xFF)]
                      ^ctx[1*256 + ((crc>>16)&0xFF)]
                      ^ctx[0*256 + ((crc>>24)     )];
            }
        while(buffer<end)
            crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);
    
        return crc;
    }
    
    #ifdef TEST
    #undef printf
    main(){
        uint8_t buf[1999];
        int i;
        int p[4][4]={{1, 32, 0xedb88320L, 0x3D5CDD04},
                     {0, 32, 0x04c11db7L, 0xC0F5BAE0},
                     {0, 16, 0x8005     , 0x1FBB    },
                     {0,  8, 0x07       , 0xE3      },};
        AVCRC ctx[1 ? 1024:257];
    
        for(i=0; i<sizeof(buf); i++)
            buf[i]= i+i*i;
    
        for(i=0; i<4; i++){
            av_crc_init(ctx, p[i][0], p[i][1], p[i][2], sizeof(ctx));
            printf("crc %08X =%X\n", p[i][2], av_crc(ctx, 0, buf, sizeof(buf)));
        }
    }
    #endif