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137 lines
6.0 KiB
C++
137 lines
6.0 KiB
C++
/*************************************************************************/
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/* random_pcg.h */
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/*************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/*************************************************************************/
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/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur. */
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/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md). */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/*************************************************************************/
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#ifndef RANDOM_PCG_H
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#define RANDOM_PCG_H
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#include <math.h>
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#include "core/math/math_defs.h"
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#include "thirdparty/misc/pcg.h"
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#if defined(__GNUC__) || (_llvm_has_builtin(__builtin_clz))
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#define CLZ32(x) __builtin_clz(x)
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#elif defined(_MSC_VER)
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#include "intrin.h"
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static int __bsr_clz32(uint32_t x) {
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unsigned long index;
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_BitScanReverse(&index, x);
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return 31 - index;
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}
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#define CLZ32(x) __bsr_clz32(x)
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#else
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#endif
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#if defined(__GNUC__) || (_llvm_has_builtin(__builtin_ldexp) && _llvm_has_builtin(__builtin_ldexpf))
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#define LDEXP(s, e) __builtin_ldexp(s, e)
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#define LDEXPF(s, e) __builtin_ldexpf(s, e)
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#else
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#include "math.h"
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#define LDEXP(s, e) ldexp(s, e)
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#define LDEXPF(s, e) ldexp(s, e)
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#endif
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class RandomPCG {
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pcg32_random_t pcg;
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uint64_t current_seed; // seed with this to get the same state
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uint64_t current_inc;
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public:
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static const uint64_t DEFAULT_SEED = 12047754176567800795U;
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static const uint64_t DEFAULT_INC = PCG_DEFAULT_INC_64;
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static const uint64_t RANDOM_MAX = 0xFFFFFFFF;
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RandomPCG(uint64_t p_seed = DEFAULT_SEED, uint64_t p_inc = DEFAULT_INC);
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_FORCE_INLINE_ void seed(uint64_t p_seed) {
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current_seed = p_seed;
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pcg32_srandom_r(&pcg, current_seed, current_inc);
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}
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_FORCE_INLINE_ uint64_t get_seed() { return current_seed; }
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void randomize();
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_FORCE_INLINE_ uint32_t rand() {
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current_seed = pcg.state;
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return pcg32_random_r(&pcg);
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}
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// Obtaining floating point numbers in [0, 1] range with "good enough" uniformity.
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// These functions sample the output of rand() as the fraction part of an infinite binary number,
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// with some tricks applied to reduce ops and branching:
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// 1. Instead of shifting to the first 1 and connecting random bits, we simply set the MSB and LSB to 1.
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// Provided that the RNG is actually uniform bit by bit, this should have the exact same effect.
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// 2. In order to compensate for exponent info loss, we count zeros from another random number,
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// and just add that to the initial offset.
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// This has the same probability as counting and shifting an actual bit stream: 2^-n for n zeroes.
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// For all numbers above 2^-96 (2^-64 for floats), the functions should be uniform.
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// However, all numbers below that threshold are floored to 0.
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// The thresholds are chosen to minimize rand() calls while keeping the numbers within a totally subjective quality standard.
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// If clz or ldexp isn't available, fall back to bit truncation for performance, sacrificing uniformity.
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_FORCE_INLINE_ double randd() {
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#if defined(CLZ32)
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uint32_t proto_exp_offset = rand();
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if (unlikely(proto_exp_offset == 0)) {
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return 0;
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}
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uint64_t significand = (((uint64_t)rand()) << 32) | rand() | 0x8000000000000001U;
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return LDEXP((double)significand, -64 - CLZ32(proto_exp_offset));
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#else
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#pragma message("RandomPCG::randd - intrinsic clz is not available, falling back to bit truncation")
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return (double)(((((uint64_t)rand()) << 32) | rand()) & 0x1FFFFFFFFFFFFFU) / (double)0x1FFFFFFFFFFFFFU;
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#endif
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}
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_FORCE_INLINE_ float randf() {
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#if defined(CLZ32)
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uint32_t proto_exp_offset = rand();
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if (unlikely(proto_exp_offset == 0)) {
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return 0;
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}
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return LDEXPF((float)(rand() | 0x80000001), -32 - CLZ32(proto_exp_offset));
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#else
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#pragma message("RandomPCG::randf - intrinsic clz is not available, falling back to bit truncation")
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return (float)(rand() & 0xFFFFFF) / (float)0xFFFFFF;
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#endif
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}
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_FORCE_INLINE_ double randfn(double p_mean, double p_deviation) {
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return p_mean + p_deviation * (cos(Math_TAU * randd()) * sqrt(-2.0 * log(randd()))); // Box-Muller transform
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}
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_FORCE_INLINE_ float randfn(float p_mean, float p_deviation) {
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return p_mean + p_deviation * (cos(Math_TAU * randf()) * sqrt(-2.0 * log(randf()))); // Box-Muller transform
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}
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double random(double p_from, double p_to);
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float random(float p_from, float p_to);
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real_t random(int p_from, int p_to) { return (real_t)random((real_t)p_from, (real_t)p_to); }
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};
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#endif // RANDOM_PCG_H
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