sfw/sfwl/core/random_pcg.h

119 lines
4.3 KiB
C++

#ifndef RANDOM_PCG_H
#define RANDOM_PCG_H
/*************************************************************************/
/* random_pcg.h */
/* From https://github.com/Relintai/pandemonium_engine (MIT) */
/*************************************************************************/
//--STRIP
#include <math.h>
#include "core/math_defs.h"
#include "core/pcg.h"
//--STRIP
#if defined(__GNUC__) || (_llvm_has_builtin(__builtin_clz))
#define CLZ32(x) __builtin_clz(x)
#elif defined(_MSC_VER)
#include "intrin.h"
static int __bsr_clz32(uint32_t x) {
unsigned long index;
_BitScanReverse(&index, x);
return 31 - index;
}
#define CLZ32(x) __bsr_clz32(x)
#else
#endif
#if defined(__GNUC__) || (_llvm_has_builtin(__builtin_ldexp) && _llvm_has_builtin(__builtin_ldexpf))
#define LDEXP(s, e) __builtin_ldexp(s, e)
#define LDEXPF(s, e) __builtin_ldexpf(s, e)
#else
#include "math.h"
#define LDEXP(s, e) ldexp(s, e)
#define LDEXPF(s, e) ldexp(s, e)
#endif
class RandomPCG {
pcg32_random_t pcg;
uint64_t current_seed; // The seed the current generator state started from.
uint64_t current_inc;
public:
static const uint64_t DEFAULT_SEED = 12047754176567800795U;
static const uint64_t DEFAULT_INC = PCG_DEFAULT_INC_64;
RandomPCG(uint64_t p_seed = DEFAULT_SEED, uint64_t p_inc = DEFAULT_INC);
_FORCE_INLINE_ void seed(uint64_t p_seed) {
current_seed = p_seed;
pcg32_srandom_r(&pcg, current_seed, current_inc);
}
_FORCE_INLINE_ uint64_t get_seed() { return current_seed; }
_FORCE_INLINE_ void set_state(uint64_t p_state) { pcg.state = p_state; }
_FORCE_INLINE_ uint64_t get_state() const { return pcg.state; }
void randomize();
_FORCE_INLINE_ uint32_t rand() {
return pcg32_random_r(&pcg);
}
_FORCE_INLINE_ uint32_t rand(uint32_t bounds) {
return pcg32_boundedrand_r(&pcg, bounds);
}
// Obtaining floating point numbers in [0, 1] range with "good enough" uniformity.
// These functions sample the output of rand() as the fraction part of an infinite binary number,
// with some tricks applied to reduce ops and branching:
// 1. Instead of shifting to the first 1 and connecting random bits, we simply set the MSB and LSB to 1.
// Provided that the RNG is actually uniform bit by bit, this should have the exact same effect.
// 2. In order to compensate for exponent info loss, we count zeros from another random number,
// and just add that to the initial offset.
// This has the same probability as counting and shifting an actual bit stream: 2^-n for n zeroes.
// For all numbers above 2^-96 (2^-64 for floats), the functions should be uniform.
// However, all numbers below that threshold are floored to 0.
// The thresholds are chosen to minimize rand() calls while keeping the numbers within a totally subjective quality standard.
// If clz or ldexp isn't available, fall back to bit truncation for performance, sacrificing uniformity.
_FORCE_INLINE_ double randd() {
#if defined(CLZ32)
uint32_t proto_exp_offset = rand();
if (unlikely(proto_exp_offset == 0)) {
return 0;
}
uint64_t significand = (((uint64_t)rand()) << 32) | rand() | 0x8000000000000001U;
return LDEXP((double)significand, -64 - CLZ32(proto_exp_offset));
#else
#pragma message("RandomPCG::randd - intrinsic clz is not available, falling back to bit truncation")
return (double)(((((uint64_t)rand()) << 32) | rand()) & 0x1FFFFFFFFFFFFFU) / (double)0x1FFFFFFFFFFFFFU;
#endif
}
_FORCE_INLINE_ float randf() {
#if defined(CLZ32)
uint32_t proto_exp_offset = rand();
if (unlikely(proto_exp_offset == 0)) {
return 0;
}
return LDEXPF((float)(rand() | 0x80000001), -32 - CLZ32(proto_exp_offset));
#else
#pragma message("RandomPCG::randf - intrinsic clz is not available, falling back to bit truncation")
return (float)(rand() & 0xFFFFFF) / (float)0xFFFFFF;
#endif
}
_FORCE_INLINE_ double randfn(double p_mean, double p_deviation) {
return p_mean + p_deviation * (cos(Math_TAU * randd()) * sqrt(-2.0 * log(randd()))); // Box-Muller transform
}
_FORCE_INLINE_ float randfn(float p_mean, float p_deviation) {
return p_mean + p_deviation * (cos(Math_TAU * randf()) * sqrt(-2.0 * log(randf()))); // Box-Muller transform
}
double random(double p_from, double p_to);
float random(float p_from, float p_to);
real_t randomr(real_t p_from, real_t p_to) { return random(p_from, p_to); }
int random(int p_from, int p_to);
};
#endif // RANDOM_PCG_H