/* * 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; }