crc.h

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/*
 * Copyright (c) 2025 Shreesh Adiga <16567adigashreesh@gmail.com>
 *
 * 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
 */
 
#ifndef AVUTIL_X86_CRC_H
#define AVUTIL_X86_CRC_H
 
#include "config.h"
#include "libavutil/attributes.h"
#include "libavutil/attributes_internal.h"
#include "libavutil/avassert.h"
#include "libavutil/cpu.h"
#include "libavutil/crc.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/reverse.h"
#include "libavutil/x86/cpu.h"
 
#if HAVE_CLMUL_EXTERNAL
FF_VISIBILITY_PUSH_HIDDEN
uint32_t ff_crc_clmul(const AVCRC *ctx, uint32_t crc,
                      const uint8_t *buffer, size_t length);
uint32_t ff_crc_le_clmul(const AVCRC *ctx, uint32_t crc,
                         const uint8_t *buffer, size_t length);
FF_VISIBILITY_POP_HIDDEN
 
enum {
    CRC_C    = 0,
    CLMUL_BE,
    CLMUL_LE,
};
 
static const AVCRC crc_table_clmul[AV_CRC_MAX][17] = {
    [AV_CRC_8_ATM] = {
        CLMUL_BE,
        0x32000000, 0x0, 0xbc000000, 0x0,
        0xc4000000, 0x0, 0x94000000, 0x0,
        0x62000000, 0x0, 0x79000000, 0x0,
        0x07156a16, 0x1, 0x07000000, 0x1,
    },
    [AV_CRC_8_EBU] = {
        CLMUL_BE,
        0xb5000000, 0x0, 0xf3000000, 0x0,
        0xfc000000, 0x0, 0x0d000000, 0x0,
        0x6a000000, 0x0, 0x65000000, 0x0,
        0x1c4b8192, 0x1, 0x1d000000, 0x1,
    },
    [AV_CRC_16_ANSI] = {
        CLMUL_BE,
        0xf9e30000, 0x0, 0x807d0000, 0x0,
        0xf9130000, 0x0, 0xff830000, 0x0,
        0x807b0000, 0x0, 0x86630000, 0x0,
        0xfffbffe7, 0x1, 0x80050000, 0x1,
    },
    [AV_CRC_16_CCITT] = {
        CLMUL_BE,
        0x60190000, 0x0, 0x59b00000, 0x0,
        0xd5f60000, 0x0, 0x45630000, 0x0,
        0xaa510000, 0x0, 0xeb230000, 0x0,
        0x11303471, 0x1, 0x10210000, 0x1,
    },
    [AV_CRC_24_IEEE] = {
        CLMUL_BE,
        0x1f428700, 0x0, 0x467d2400, 0x0,
        0x2c8c9d00, 0x0, 0x64e4d700, 0x0,
        0xd9fe8c00, 0x0, 0xfd7e0c00, 0x0,
        0xf845fe24, 0x1, 0x864cfb00, 0x1,
    },
    [AV_CRC_32_IEEE] = {
        CLMUL_BE,
        0x8833794c, 0x0, 0xe6228b11, 0x0,
        0xc5b9cd4c, 0x0, 0xe8a45605, 0x0,
        0x490d678d, 0x0, 0xf200aa66, 0x0,
        0x04d101df, 0x1, 0x04c11db7, 0x1,
    },
    [AV_CRC_32_IEEE_LE] = {
        CLMUL_LE,
        0xc6e41596, 0x1, 0x54442bd4, 0x1,
        0xccaa009e, 0x0, 0x751997d0, 0x1,
        0xccaa009e, 0x0, 0x63cd6124, 0x1,
        0xf7011640, 0x1, 0xdb710641, 0x1,
    },
    [AV_CRC_16_ANSI_LE] = {
        CLMUL_LE,
        0x0000bffa, 0x0, 0x1b0c2, 0x0,
        0x00018cc2, 0x0, 0x1d0c2, 0x0,
        0x00018cc2, 0x0, 0x1bc02, 0x0,
        0xcfffbffe, 0x1, 0x14003, 0x0,
    },
};
 
static uint64_t reverse(uint64_t p, unsigned int deg)
{
    uint64_t ret = 0;
    int i;
    for (i = 0; i < (deg / 8); i += 1) {
        ret = (ret << 8) | (ff_reverse[p & 0xff]);
        p >>= 8;
    }
    int rem = (deg + 1) - 8 * i;
    ret = (ret << rem) | (ff_reverse[p & 0xff] >> (8 - rem));
    return ret;
}
 
static uint64_t xnmodp(unsigned n, uint64_t poly, unsigned deg, uint64_t *div, int bitreverse)
{
    uint64_t mod, mask, high;
 
    if (n < deg) {
        *div = 0;
        return poly;
    }
    mask = ((uint64_t)1 << deg) - 1;
    poly &= mask;
    mod = poly;
    *div = 1;
    deg--;
    while (--n > deg) {
        high = (mod >> deg) & 1;
        *div = (*div << 1) | high;
        mod <<= 1;
        if (high)
            mod ^= poly;
    }
    uint64_t ret = mod & mask;
    if (bitreverse) {
        *div = reverse(*div, deg) << 1;
        return reverse(ret, deg) << 1;
    }
    return ret;
}
 
static inline void crc_init_x86(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
{
    uint64_t poly_;
    if (le) {
        // convert the reversed representation to regular form
        poly = reverse(poly, bits) >> 1;
    }
    // convert to 32 degree polynomial
    poly_ = ((uint64_t)poly) << (32 - bits);
 
    uint64_t div;
    uint8_t *dst = (uint8_t*)(ctx + 1);
    if (le) {
        ctx[0] = CLMUL_LE;
        AV_WN64(dst,      xnmodp(4 * 128 - 32, poly_, 32, &div, le));
        AV_WN64(dst +  8, xnmodp(4 * 128 + 32, poly_, 32, &div, le));
        uint64_t tmp = xnmodp(128 - 32, poly_, 32, &div, le);
        AV_WN64(dst + 16, tmp);
        AV_WN64(dst + 24, xnmodp(128 + 32, poly_, 32, &div, le));
        AV_WN64(dst + 32, tmp);
        AV_WN64(dst + 40, xnmodp(64, poly_, 32, &div, le));
        AV_WN64(dst + 48, div);
        AV_WN64(dst + 56, reverse(poly_ | (1ULL << 32), 32));
    } else {
        ctx[0] = CLMUL_BE;
        AV_WN64(dst,      xnmodp(4 * 128 + 64, poly_, 32, &div, le));
        AV_WN64(dst +  8, xnmodp(4 * 128, poly_, 32, &div, le));
        AV_WN64(dst + 16, xnmodp(128 + 64, poly_, 32, &div, le));
        AV_WN64(dst + 24, xnmodp(128, poly_, 32, &div, le));
        AV_WN64(dst + 32, xnmodp(64, poly_, 32, &div, le));
        AV_WN64(dst + 48, div);
        AV_WN64(dst + 40, xnmodp(96, poly_, 32, &div, le));
        AV_WN64(dst + 56, poly_ | (1ULL << 32));
    }
}
#endif
 
static inline const AVCRC *ff_crc_get_table_x86(AVCRCId crc_id)
{
#if HAVE_CLMUL_EXTERNAL
    int cpu_flags = av_get_cpu_flags();
 
    if (EXTERNAL_CLMUL(cpu_flags)) {
        return crc_table_clmul[crc_id];
    }
#endif
    return NULL;
}
 
static inline av_cold int ff_crc_init_x86(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
{
#if HAVE_CLMUL_EXTERNAL
    int cpu_flags = av_get_cpu_flags();
 
    if (EXTERNAL_CLMUL(cpu_flags)) {
        crc_init_x86(ctx, le, bits, poly, ctx_size);
        return 1;
    }
#endif
    return 0;
}
 
static inline uint32_t ff_crc_x86(const AVCRC *ctx, uint32_t crc,
                                  const uint8_t *buffer, size_t length)
{
    switch (ctx[0]) {
#if HAVE_CLMUL_EXTERNAL
    case CLMUL_BE: return ff_crc_clmul(ctx, crc, buffer, length);
    case CLMUL_LE: return ff_crc_le_clmul(ctx, crc, buffer, length);
#endif
    default: av_unreachable("x86 CRC only uses CLMUL_BE and CLMUL_LE");
    }
    return 0;
}
 
#endif /* AVUTIL_X86_CRC_H */