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