mirror of
https://github.com/love2d/love.git
synced 2026-08-13 17:10:54 +02:00
Alex Szpakowski
144 lines
4.1 KiB
C++
144 lines
4.1 KiB
C++
/**
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* Copyright (c) 2006-2016 LOVE Development Team
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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**/
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#include "RandomGenerator.h"
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// C++
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#include <sstream>
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#include <iomanip>
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// C
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#include <cmath>
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#include <cstdlib>
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namespace love
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{
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namespace math
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{
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// Thomas Wang's 64-bit integer hashing function:
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// https://web.archive.org/web/20110807030012/http://www.cris.com/%7ETtwang/tech/inthash.htm
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static uint64 wangHash64(uint64 key)
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{
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key = (~key) + (key << 21); // key = (key << 21) - key - 1;
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key = key ^ (key >> 24);
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key = (key + (key << 3)) + (key << 8); // key * 265
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key = key ^ (key >> 14);
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key = (key + (key << 2)) + (key << 4); // key * 21
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key = key ^ (key >> 28);
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key = key + (key << 31);
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return key;
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}
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// 64 bit Xorshift implementation taken from the end of Sec. 3 (page 4) in
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// George Marsaglia, "Xorshift RNGs", Journal of Statistical Software, Vol.8 (Issue 14), 2003
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// Use an 'Xorshift*' variant, as shown here: http://xorshift.di.unimi.it
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RandomGenerator::RandomGenerator()
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: last_randomnormal(std::numeric_limits<double>::infinity())
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{
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// because it is too big for some compilers to handle ... if you know what
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// i mean
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Seed newseed;
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newseed.b32.low = 0xCBBF7A44;
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newseed.b32.high = 0x0139408D;
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setSeed(newseed);
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}
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uint64 RandomGenerator::rand()
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{
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rng_state.b64 ^= (rng_state.b64 >> 12);
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rng_state.b64 ^= (rng_state.b64 << 25);
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rng_state.b64 ^= (rng_state.b64 >> 27);
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return rng_state.b64 * 2685821657736338717ULL;
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}
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// Box–Muller transform
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double RandomGenerator::randomNormal(double stddev)
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{
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// use cached number if possible
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if (last_randomnormal != std::numeric_limits<double>::infinity())
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{
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double r = last_randomnormal;
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last_randomnormal = std::numeric_limits<double>::infinity();
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return r * stddev;
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}
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double r = sqrt(-2.0 * log(1. - random()));
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double phi = 2.0 * LOVE_M_PI * (1. - random());
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last_randomnormal = r * cos(phi);
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return r * sin(phi) * stddev;
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}
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void RandomGenerator::setSeed(RandomGenerator::Seed newseed)
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{
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seed = newseed;
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// Xorshift isn't designed to give a good distribution of values across many
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// similar seeds, so we hash the state integer before using it.
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// http://www.reedbeta.com/blog/2013/01/12/quick-and-easy-gpu-random-numbers-in-d3d11/
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// Xorshift also can't handle a state value of 0, so we avoid that.
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do
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{
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newseed.b64 = wangHash64(newseed.b64);
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} while (newseed.b64 == 0);
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rng_state = newseed;
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}
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RandomGenerator::Seed RandomGenerator::getSeed() const
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{
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return seed;
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}
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void RandomGenerator::setState(const std::string &statestr)
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{
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// For this implementation we'll accept a hex string representing the
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// 64-bit state integer xorshift uses.
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// Hex string must start with 0x.
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if (statestr.find("0x") != 0 || statestr.size() < 3)
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throw love::Exception("Invalid random state: %s", statestr.c_str());
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Seed state = {};
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char *end = nullptr;
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state.b64 = strtoull(statestr.c_str(), &end, 16);
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if (end != nullptr && *end != 0)
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throw love::Exception("Invalid random state: %s", statestr.c_str());
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rng_state = state;
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}
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std::string RandomGenerator::getState() const
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{
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// For this implementation we'll return a hex string representing the 64-bit
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// state integer xorshift uses.
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std::stringstream ss;
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ss << "0x" << std::setfill('0') << std::setw(16) << std::hex << rng_state.b64;
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return ss.str();
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}
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} // math
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} // love
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