88 lines
2.5 KiB
C
88 lines
2.5 KiB
C
/*
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* Lagged Fibonacci PRNG
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* Copyright (c) 2008 Michael Niedermayer
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*
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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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#include <inttypes.h>
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#include <limits.h>
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#include <math.h>
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#include "lfg.h"
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#include "crc.h"
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#include "md5.h"
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#include "error.h"
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#include "intreadwrite.h"
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#include "attributes.h"
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av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
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{
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uint8_t tmp[16] = { 0 };
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int i;
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for (i = 8; i < 64; i += 4) {
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AV_WL32(tmp, seed);
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tmp[4] = i;
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av_md5_sum(tmp, tmp, 16);
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c->state[i ] = AV_RL32(tmp);
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c->state[i + 1] = AV_RL32(tmp + 4);
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c->state[i + 2] = AV_RL32(tmp + 8);
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c->state[i + 3] = AV_RL32(tmp + 12);
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}
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c->index = 0;
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}
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void av_bmg_get(AVLFG *lfg, double out[2])
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{
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double x1, x2, w;
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do {
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x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
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x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
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w = x1 * x1 + x2 * x2;
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} while (w >= 1.0);
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w = sqrt((-2.0 * log(w)) / w);
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out[0] = x1 * w;
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out[1] = x2 * w;
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}
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int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length) {
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unsigned int beg, end, segm;
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const AVCRC *avcrc;
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uint32_t crc = 1;
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/* avoid integer overflow in the loop below. */
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if (length > (UINT_MAX / 128U)) return AVERROR(EINVAL);
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c->index = 0;
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avcrc = av_crc_get_table(AV_CRC_32_IEEE); /* This can't fail. It's a well-defined table in crc.c */
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/* across 64 segments of the incoming data,
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* do a running crc of each segment and store the crc as the state for that slot.
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* this works even if the length of the segment is 0 bytes. */
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beg = 0;
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for (segm = 0;segm < 64;segm++) {
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end = (((segm + 1) * length) / 64);
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crc = av_crc(avcrc, crc, data + beg, end - beg);
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c->state[segm] = (unsigned int)crc;
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beg = end;
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}
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return 0;
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}
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