PeerStreamer

/*

 * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * FFmpeg is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include "common.h"

#include "crc.h"

#ifdef CONFIG_HARDCODED_TABLES

#include "crc_data.h"

#else

static struct {

    uint8_t  le;

    uint8_t  bits;

    uint32_t poly;

} av_crc_table_params[AV_CRC_MAX] = {

    [AV_CRC_8_ATM]      = { 0,  8,       0x07 },

    [AV_CRC_16_ANSI]    = { 0, 16,     0x8005 },

    [AV_CRC_16_CCITT]   = { 0, 16,     0x1021 },

    [AV_CRC_32_IEEE]    = { 0, 32, 0x04C11DB7 },

    [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },

};

static AVCRC av_crc_table[AV_CRC_MAX][257];

#endif

/**

 * 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

 * @param le if 1, lowest bit represents coefficient for highest exponent

 *           of corresponding polynomial (both for poly and actual CRC).

 *           If 0, you must swap the crc parameter and the result of av_crc

 *           if you need the standard representation (can be simplified in

 *           most cases to e.g. bswap16):

 *           bswap_32(crc << (32-bits))

 * @param bits number of bits for the CRC

 * @param poly generator polynomial without the x**bits coefficient, in the

 *             representation as specified by le

 * @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;

#ifndef CONFIG_SMALL

    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 ];

#endif

    return 0;

}

/**

 * Get an initialized standard CRC table.

 * @param crc_id ID of a standard CRC

 * @return a pointer to the CRC table or NULL on failure

 */

const AVCRC *av_crc_get_table(AVCRCId crc_id){

#ifndef CONFIG_HARDCODED_TABLES

    if (!av_crc_table[crc_id][sizeof(av_crc_table[crc_id])/sizeof(av_crc_table[crc_id][0])-1])

        if (av_crc_init(av_crc_table[crc_id],

                        av_crc_table_params[crc_id].le,

                        av_crc_table_params[crc_id].bits,

                        av_crc_table_params[crc_id].poly,

                        sizeof(av_crc_table[crc_id])) < 0)

            return NULL;

#endif

    return av_crc_table[crc_id];

}

/**

 * Calculate the CRC of a block

 * @param crc CRC of previous blocks if any or initial value for CRC.

 * @return CRC updated with the data from the given block

 *

 * @see av_crc_init() "le" parameter

 */

uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length){

    const uint8_t *end= buffer+length;

#ifndef CONFIG_SMALL

    if(!ctx[256])

        while(buffer<end-3){

            crc ^= le2me_32(*(const 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)     )];

        }

#endif

    while(buffer<end)

        crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);

    return crc;

}

#ifdef TEST

#undef printf

int main(void){

    uint8_t buf[1999];

    int i;

    int p[4][3]={{AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04},

                 {AV_CRC_32_IEEE   , 0x04C11DB7, 0xC0F5BAE0},

                 {AV_CRC_16_ANSI   , 0x8005,     0x1FBB    },

                 {AV_CRC_8_ATM     , 0x07,       0xE3      },};

    const AVCRC *ctx;

    for(i=0; i<sizeof(buf); i++)

        buf[i]= i+i*i;

    for(i=0; i<4; i++){

        ctx = av_crc_get_table(p[i][0]);

        printf("crc %08X =%X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));

    }

    return 0;

}

#endif