crc.c 5.18 KB
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/*
 * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
 *
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 * This file is part of FFmpeg.
 *
 * 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
 * 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
 * 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
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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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#include "config.h"
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#include "common.h"
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#include "bswap.h"
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#include "crc.h"

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#if CONFIG_HARDCODED_TABLES
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#include "crc_data.h"
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#else
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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];
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#endif
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/**
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 * Initialize a CRC table.
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 * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
 * @param le If 1, the lowest bit represents the coefficient for the highest
 *           exponent of the corresponding polynomial (both for poly and
 *           actual CRC).
 *           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
 *           most cases to e.g. bswap16):
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 *           av_bswap32(crc << (32-bits))
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 * @param bits number of bits for the CRC
 * @param poly generator polynomial without the x**bits coefficient, in the
 *             representation as specified by le
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 * @param ctx_size size of ctx in bytes
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 * @return <0 on failure
 */
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int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
{
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    unsigned 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;

    for (i = 0; i < 256; i++) {
        if (le) {
            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;
        } else {
            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] = av_bswap32(c);
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        }
    }
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    ctx[256] = 1;
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#if !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++)
                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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 * Get an initialized standard CRC table.
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 * @param crc_id ID of a standard CRC
 * @return a pointer to the CRC table or NULL on failure
 */
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const AVCRC *av_crc_get_table(AVCRCId crc_id)
{
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#if !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],
                        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];
}

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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
 *
 * @see av_crc_init() "le" parameter
 */
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uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
                const uint8_t *buffer, size_t length)
{
    const uint8_t *end = buffer + length;
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#if !CONFIG_SMALL
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    if (!ctx[256]) {
        while (((intptr_t) buffer & 3) && buffer < end)
            crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
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        while (buffer < end - 3) {
            crc ^= av_le2ne32(*(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)       )];
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        }
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    }
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#endif
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    while (buffer < end)
        crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
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    return crc;
}

#ifdef TEST
#undef printf
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int main(void)
{
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    uint8_t buf[1999];
    int i;
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    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       }
    };
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    const AVCRC *ctx;
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    for (i = 0; i < sizeof(buf); i++)
        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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}
#endif