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952e588600
Move the reverse and xnmodp functions to a separate header so that it can be reused for aarch64 implementation of av_crc.
67 lines
1.8 KiB
C
67 lines
1.8 KiB
C
/*
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* This file is part of FFmpeg.
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*
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* 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
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* 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
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* 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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*/
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#ifndef AVUTIL_CRC_INTERNAL_H
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#define AVUTIL_CRC_INTERNAL_H
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#include <stdint.h>
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#include "libavutil/reverse.h"
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static uint64_t reverse(uint64_t p, unsigned int deg)
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{
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uint64_t ret = 0;
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int i;
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for (i = 0; i < (deg / 8); i += 1) {
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ret = (ret << 8) | (ff_reverse[p & 0xff]);
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p >>= 8;
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}
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int rem = (deg + 1) - 8 * i;
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ret = (ret << rem) | (ff_reverse[p & 0xff] >> (8 - rem));
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return ret;
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}
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static uint64_t xnmodp(unsigned n, uint64_t poly, unsigned deg, uint64_t *div, int bitreverse)
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{
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uint64_t mod, mask, high;
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if (n < deg) {
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*div = 0;
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return poly;
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}
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mask = ((uint64_t)1 << deg) - 1;
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poly &= mask;
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mod = poly;
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*div = 1;
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deg--;
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while (--n > deg) {
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high = (mod >> deg) & 1;
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*div = (*div << 1) | high;
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mod <<= 1;
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if (high)
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mod ^= poly;
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}
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uint64_t ret = mod & mask;
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if (bitreverse) {
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*div = reverse(*div, deg) << 1;
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return reverse(ret, deg) << 1;
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}
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return ret;
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}
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#endif /* AVUTIL_CRC_INTERNAL_H */
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