1/* 2 * Lagged Fibonacci PRNG 3 * Copyright (c) 2008 Michael Niedermayer 4 * 5 * This file is part of FFmpeg. 6 * 7 * FFmpeg is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2.1 of the License, or (at your option) any later version. 11 * 12 * FFmpeg is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with FFmpeg; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22#include <inttypes.h> 23#include <limits.h> 24#include <math.h> 25#include "lfg.h" 26#include "crc.h" 27#include "md5.h" 28#include "error.h" 29#include "intreadwrite.h" 30#include "attributes.h" 31 32av_cold void av_lfg_init(AVLFG *c, unsigned int seed) 33{ 34 uint8_t tmp[16] = { 0 }; 35 int i; 36 37 for (i = 8; i < 64; i += 4) { 38 AV_WL32(tmp, seed); 39 tmp[4] = i; 40 av_md5_sum(tmp, tmp, 16); 41 c->state[i ] = AV_RL32(tmp); 42 c->state[i + 1] = AV_RL32(tmp + 4); 43 c->state[i + 2] = AV_RL32(tmp + 8); 44 c->state[i + 3] = AV_RL32(tmp + 12); 45 } 46 c->index = 0; 47} 48 49void av_bmg_get(AVLFG *lfg, double out[2]) 50{ 51 double x1, x2, w; 52 53 do { 54 x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; 55 x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; 56 w = x1 * x1 + x2 * x2; 57 } while (w >= 1.0); 58 59 w = sqrt((-2.0 * log(w)) / w); 60 out[0] = x1 * w; 61 out[1] = x2 * w; 62} 63 64int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length) { 65 unsigned int beg, end, segm; 66 const AVCRC *avcrc; 67 uint32_t crc = 1; 68 69 /* avoid integer overflow in the loop below. */ 70 if (length > (UINT_MAX / 128U)) return AVERROR(EINVAL); 71 72 c->index = 0; 73 avcrc = av_crc_get_table(AV_CRC_32_IEEE); /* This can't fail. It's a well-defined table in crc.c */ 74 75 /* across 64 segments of the incoming data, 76 * do a running crc of each segment and store the crc as the state for that slot. 77 * this works even if the length of the segment is 0 bytes. */ 78 beg = 0; 79 for (segm = 0;segm < 64;segm++) { 80 end = (((segm + 1) * length) / 64); 81 crc = av_crc(avcrc, crc, data + beg, end - beg); 82 c->state[segm] = (unsigned int)crc; 83 beg = end; 84 } 85 86 return 0; 87} 88