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common: Add implementation of TinyMT (Mersenne Twister RNG).

This commit is contained in:
bunnei 2021-02-08 18:05:13 -08:00
parent 6da91da08e
commit c9235764c7
2 changed files with 251 additions and 0 deletions
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1
src/common/CMakeLists.txt
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@ -167,6 +167,7 @@ add_library(common STATIC
threadsafe_queue.h
time_zone.cpp
time_zone.h
tiny_mt.h
tree.h
uint128.h
uuid.cpp

250
src/common/tiny_mt.h Normal file
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@ -0,0 +1,250 @@
// Copyright 2021 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
#pragma once
#include <array>
#include "common/alignment.h"
#include "common/common_types.h"
namespace Common {
// Implementation of TinyMT (mersenne twister RNG).
// Like Nintendo, we will use the sample parameters.
class TinyMT {
public:
static constexpr std::size_t NumStateWords = 4;
struct State {
std::array<u32, NumStateWords> data{};
};
private:
static constexpr u32 ParamMat1 = 0x8F7011EE;
static constexpr u32 ParamMat2 = 0xFC78FF1F;
static constexpr u32 ParamTmat = 0x3793FDFF;
static constexpr u32 ParamMult = 0x6C078965;
static constexpr u32 ParamPlus = 0x0019660D;
static constexpr u32 ParamXor = 0x5D588B65;
static constexpr u32 TopBitmask = 0x7FFFFFFF;
static constexpr int MinimumInitIterations = 8;
static constexpr int NumDiscardedInitOutputs = 8;
static constexpr u32 XorByShifted27(u32 value) {
return value ^ (value >> 27);
}
static constexpr u32 XorByShifted30(u32 value) {
return value ^ (value >> 30);
}
private:
State state{};
private:
// Internal API.
void FinalizeInitialization() {
const u32 state0 = this->state.data[0] & TopBitmask;
const u32 state1 = this->state.data[1];
const u32 state2 = this->state.data[2];
const u32 state3 = this->state.data[3];
if (state0 == 0 && state1 == 0 && state2 == 0 && state3 == 0) {
this->state.data[0] = 'T';
this->state.data[1] = 'I';
this->state.data[2] = 'N';
this->state.data[3] = 'Y';
}
for (int i = 0; i < NumDiscardedInitOutputs; i++) {
this->GenerateRandomU32();
}
}
u32 GenerateRandomU24() {
return (this->GenerateRandomU32() >> 8);
}
static void GenerateInitialValuePlus(TinyMT::State* state, int index, u32 value) {
u32& state0 = state->data[(index + 0) % NumStateWords];
u32& state1 = state->data[(index + 1) % NumStateWords];
u32& state2 = state->data[(index + 2) % NumStateWords];
u32& state3 = state->data[(index + 3) % NumStateWords];
const u32 x = XorByShifted27(state0 ^ state1 ^ state3) * ParamPlus;
const u32 y = x + index + value;
state0 = y;
state1 += x;
state2 += y;
}
static void GenerateInitialValueXor(TinyMT::State* state, int index) {
u32& state0 = state->data[(index + 0) % NumStateWords];
u32& state1 = state->data[(index + 1) % NumStateWords];
u32& state2 = state->data[(index + 2) % NumStateWords];
u32& state3 = state->data[(index + 3) % NumStateWords];
const u32 x = XorByShifted27(state0 + state1 + state3) * ParamXor;
const u32 y = x - index;
state0 = y;
state1 ^= x;
state2 ^= y;
}
public:
constexpr TinyMT() = default;
// Public API.
// Initialization.
void Initialize(u32 seed) {
this->state.data[0] = seed;
this->state.data[1] = ParamMat1;
this->state.data[2] = ParamMat2;
this->state.data[3] = ParamTmat;
for (int i = 1; i < MinimumInitIterations; i++) {
const u32 mixed = XorByShifted30(this->state.data[(i - 1) % NumStateWords]);
this->state.data[i % NumStateWords] ^= mixed * ParamMult + i;
}
this->FinalizeInitialization();
}
void Initialize(const u32* seed, int seed_count) {
this->state.data[0] = 0;
this->state.data[1] = ParamMat1;
this->state.data[2] = ParamMat2;
this->state.data[3] = ParamTmat;
{
const int num_init_iterations = std::max(seed_count + 1, MinimumInitIterations) - 1;
GenerateInitialValuePlus(&this->state, 0, seed_count);
for (int i = 0; i < num_init_iterations; i++) {
GenerateInitialValuePlus(&this->state, (i + 1) % NumStateWords,
(i < seed_count) ? seed[i] : 0);
}
for (int i = 0; i < static_cast<int>(NumStateWords); i++) {
GenerateInitialValueXor(&this->state,
(i + 1 + num_init_iterations) % NumStateWords);
}
}
this->FinalizeInitialization();
}
// State management.
void GetState(TinyMT::State& out) const {
out.data = this->state.data;
}
void SetState(const TinyMT::State& state_) {
this->state.data = state_.data;
}
// Random generation.
void GenerateRandomBytes(void* dst, std::size_t size) {
const uintptr_t start = reinterpret_cast<uintptr_t>(dst);
const uintptr_t end = start + size;
const uintptr_t aligned_start = Common::AlignUp(start, 4);
const uintptr_t aligned_end = Common::AlignDown(end, 4);
// Make sure we're aligned.
if (start < aligned_start) {
const u32 rnd = this->GenerateRandomU32();
std::memcpy(dst, &rnd, aligned_start - start);
}
// Write as many aligned u32s as we can.
{
u32* cur_dst = reinterpret_cast<u32*>(aligned_start);
u32* const end_dst = reinterpret_cast<u32*>(aligned_end);
while (cur_dst < end_dst) {
*(cur_dst++) = this->GenerateRandomU32();
}
}
// Handle any leftover unaligned data.
if (aligned_end < end) {
const u32 rnd = this->GenerateRandomU32();
std::memcpy(reinterpret_cast<void*>(aligned_end), &rnd, end - aligned_end);
}
}
u32 GenerateRandomU32() {
// Advance state.
const u32 x0 =
(this->state.data[0] & TopBitmask) ^ this->state.data[1] ^ this->state.data[2];
const u32 y0 = this->state.data[3];
const u32 x1 = x0 ^ (x0 << 1);
const u32 y1 = y0 ^ (y0 >> 1) ^ x1;
const u32 state0 = this->state.data[1];
u32 state1 = this->state.data[2];
u32 state2 = x1 ^ (y1 << 10);
const u32 state3 = y1;
if ((y1 & 1) != 0) {
state1 ^= ParamMat1;
state2 ^= ParamMat2;
}
this->state.data[0] = state0;
this->state.data[1] = state1;
this->state.data[2] = state2;
this->state.data[3] = state3;
// Temper.
const u32 t1 = state0 + (state2 >> 8);
u32 t0 = state3 ^ t1;
if ((t1 & 1) != 0) {
t0 ^= ParamTmat;
}
return t0;
}
u64 GenerateRandomU64() {
const u32 lo = this->GenerateRandomU32();
const u32 hi = this->GenerateRandomU32();
return (u64{hi} << 32) | u64{lo};
}
float GenerateRandomF32() {
// Floats have 24 bits of mantissa.
constexpr u32 MantissaBits = 24;
return static_cast<float>(GenerateRandomU24()) * (1.0f / (1U << MantissaBits));
}
double GenerateRandomF64() {
// Doubles have 53 bits of mantissa.
// The smart way to generate 53 bits of random would be to use 32 bits
// from the first rnd32() call, and then 21 from the second.
// Nintendo does not. They use (32 - 5) = 27 bits from the first rnd32()
// call, and (32 - 6) bits from the second. We'll do what they do, but
// There's not a clear reason why.
constexpr u32 MantissaBits = 53;
constexpr u32 Shift1st = (64 - MantissaBits) / 2;
constexpr u32 Shift2nd = (64 - MantissaBits) - Shift1st;
const u32 first = (this->GenerateRandomU32() >> Shift1st);
const u32 second = (this->GenerateRandomU32() >> Shift2nd);
return (1.0 * first * (u64{1} << (32 - Shift2nd)) + second) *
(1.0 / (u64{1} << MantissaBits));
}
};
} // namespace Common