1/**
2 * Copyright (c) 2006-2023 LOVE Development Team
3 *
4 * This software is provided 'as-is', without any express or implied
5 * warranty. In no event will the authors be held liable for any damages
6 * arising from the use of this software.
7 *
8 * Permission is granted to anyone to use this software for any purpose,
9 * including commercial applications, and to alter it and redistribute it
10 * freely, subject to the following restrictions:
11 *
12 * 1. The origin of this software must not be misrepresented; you must not
13 * claim that you wrote the original software. If you use this software
14 * in a product, an acknowledgment in the product documentation would be
15 * appreciated but is not required.
16 * 2. Altered source versions must be plainly marked as such, and must not be
17 * misrepresented as being the original software.
18 * 3. This notice may not be removed or altered from any source distribution.
19 **/
20
21#include "RandomGenerator.h"
22
23// C++
24#include <sstream>
25#include <iomanip>
26
27// C
28#include <cmath>
29#include <cstdlib>
30
31namespace love
32{
33namespace math
34{
35
36// Thomas Wang's 64-bit integer hashing function:
37// https://web.archive.org/web/20110807030012/http://www.cris.com/%7ETtwang/tech/inthash.htm
38static uint64 wangHash64(uint64 key)
39{
40 key = (~key) + (key << 21); // key = (key << 21) - key - 1;
41 key = key ^ (key >> 24);
42 key = (key + (key << 3)) + (key << 8); // key * 265
43 key = key ^ (key >> 14);
44 key = (key + (key << 2)) + (key << 4); // key * 21
45 key = key ^ (key >> 28);
46 key = key + (key << 31);
47 return key;
48}
49
50love::Type RandomGenerator::type("RandomGenerator", &Object::type);
51
52// 64 bit Xorshift implementation taken from the end of Sec. 3 (page 4) in
53// George Marsaglia, "Xorshift RNGs", Journal of Statistical Software, Vol.8 (Issue 14), 2003
54// Use an 'Xorshift*' variant, as shown here: http://xorshift.di.unimi.it
55
56RandomGenerator::RandomGenerator()
57 : last_randomnormal(std::numeric_limits<double>::infinity())
58{
59 // because it is too big for some compilers to handle ... if you know what
60 // i mean
61 Seed newseed;
62 newseed.b32.low = 0xCBBF7A44;
63 newseed.b32.high = 0x0139408D;
64 setSeed(newseed);
65}
66
67uint64 RandomGenerator::rand()
68{
69 rng_state.b64 ^= (rng_state.b64 >> 12);
70 rng_state.b64 ^= (rng_state.b64 << 25);
71 rng_state.b64 ^= (rng_state.b64 >> 27);
72 return rng_state.b64 * 2685821657736338717ULL;
73}
74
75// Box–Muller transform
76double RandomGenerator::randomNormal(double stddev)
77{
78 // use cached number if possible
79 if (last_randomnormal != std::numeric_limits<double>::infinity())
80 {
81 double r = last_randomnormal;
82 last_randomnormal = std::numeric_limits<double>::infinity();
83 return r * stddev;
84 }
85
86 double r = sqrt(-2.0 * log(1. - random()));
87 double phi = 2.0 * LOVE_M_PI * (1. - random());
88
89 last_randomnormal = r * cos(phi);
90 return r * sin(phi) * stddev;
91}
92
93void RandomGenerator::setSeed(RandomGenerator::Seed newseed)
94{
95 seed = newseed;
96
97 // Xorshift isn't designed to give a good distribution of values across many
98 // similar seeds, so we hash the state integer before using it.
99 // http://www.reedbeta.com/blog/2013/01/12/quick-and-easy-gpu-random-numbers-in-d3d11/
100 // Xorshift also can't handle a state value of 0, so we avoid that.
101 do
102 {
103 newseed.b64 = wangHash64(newseed.b64);
104 } while (newseed.b64 == 0);
105
106 rng_state = newseed;
107
108 last_randomnormal = std::numeric_limits<double>::infinity();
109}
110
111RandomGenerator::Seed RandomGenerator::getSeed() const
112{
113 return seed;
114}
115
116void RandomGenerator::setState(const std::string &statestr)
117{
118 // For this implementation we'll accept a hex string representing the
119 // 64-bit state integer xorshift uses.
120
121 // Hex string must start with 0x.
122 if (statestr.find("0x") != 0 || statestr.size() < 3)
123 throw love::Exception("Invalid random state: %s", statestr.c_str());
124
125 Seed state = {};
126
127 char *end = nullptr;
128 state.b64 = strtoull(statestr.c_str(), &end, 16);
129
130 if (end != nullptr && *end != 0)
131 throw love::Exception("Invalid random state: %s", statestr.c_str());
132
133 rng_state = state;
134
135 last_randomnormal = std::numeric_limits<double>::infinity();
136}
137
138std::string RandomGenerator::getState() const
139{
140 // For this implementation we'll return a hex string representing the 64-bit
141 // state integer xorshift uses.
142 std::stringstream ss;
143 ss << "0x" << std::setfill('0') << std::setw(16) << std::hex << rng_state.b64;
144
145 return ss.str();
146}
147
148} // math
149} // love
150