blob: 46b04d24039f416dd84a6668c65cc323eaa6b6c2
| 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 | |
| 32 | av_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 | |
| 49 | void 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 | |
| 64 | int 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 |