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249 lines
7.7 KiB
C++
249 lines
7.7 KiB
C++
// SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
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// SPDX-License-Identifier: GPL-2.0-or-later
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#pragma once
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#include <array>
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#include "common/alignment.h"
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#include "common/common_types.h"
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namespace Common {
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// Implementation of TinyMT (mersenne twister RNG).
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// Like Nintendo, we will use the sample parameters.
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class TinyMT {
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public:
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static constexpr std::size_t NumStateWords = 4;
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struct State {
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std::array<u32, NumStateWords> data{};
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};
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private:
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static constexpr u32 ParamMat1 = 0x8F7011EE;
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static constexpr u32 ParamMat2 = 0xFC78FF1F;
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static constexpr u32 ParamTmat = 0x3793FDFF;
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static constexpr u32 ParamMult = 0x6C078965;
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static constexpr u32 ParamPlus = 0x0019660D;
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static constexpr u32 ParamXor = 0x5D588B65;
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static constexpr u32 TopBitmask = 0x7FFFFFFF;
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static constexpr int MinimumInitIterations = 8;
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static constexpr int NumDiscardedInitOutputs = 8;
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static constexpr u32 XorByShifted27(u32 value) {
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return value ^ (value >> 27);
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}
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static constexpr u32 XorByShifted30(u32 value) {
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return value ^ (value >> 30);
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}
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private:
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State state{};
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private:
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// Internal API.
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void FinalizeInitialization() {
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const u32 state0 = this->state.data[0] & TopBitmask;
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const u32 state1 = this->state.data[1];
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const u32 state2 = this->state.data[2];
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const u32 state3 = this->state.data[3];
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if (state0 == 0 && state1 == 0 && state2 == 0 && state3 == 0) {
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this->state.data[0] = 'T';
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this->state.data[1] = 'I';
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this->state.data[2] = 'N';
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this->state.data[3] = 'Y';
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}
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for (int i = 0; i < NumDiscardedInitOutputs; i++) {
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this->GenerateRandomU32();
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}
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}
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u32 GenerateRandomU24() {
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return (this->GenerateRandomU32() >> 8);
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}
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static void GenerateInitialValuePlus(TinyMT::State* state, int index, u32 value) {
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u32& state0 = state->data[(index + 0) % NumStateWords];
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u32& state1 = state->data[(index + 1) % NumStateWords];
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u32& state2 = state->data[(index + 2) % NumStateWords];
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u32& state3 = state->data[(index + 3) % NumStateWords];
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const u32 x = XorByShifted27(state0 ^ state1 ^ state3) * ParamPlus;
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const u32 y = x + index + value;
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state0 = y;
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state1 += x;
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state2 += y;
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}
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static void GenerateInitialValueXor(TinyMT::State* state, int index) {
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u32& state0 = state->data[(index + 0) % NumStateWords];
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u32& state1 = state->data[(index + 1) % NumStateWords];
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u32& state2 = state->data[(index + 2) % NumStateWords];
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u32& state3 = state->data[(index + 3) % NumStateWords];
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const u32 x = XorByShifted27(state0 + state1 + state3) * ParamXor;
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const u32 y = x - index;
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state0 = y;
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state1 ^= x;
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state2 ^= y;
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}
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public:
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constexpr TinyMT() = default;
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// Public API.
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// Initialization.
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void Initialize(u32 seed) {
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this->state.data[0] = seed;
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this->state.data[1] = ParamMat1;
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this->state.data[2] = ParamMat2;
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this->state.data[3] = ParamTmat;
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for (int i = 1; i < MinimumInitIterations; i++) {
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const u32 mixed = XorByShifted30(this->state.data[(i - 1) % NumStateWords]);
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this->state.data[i % NumStateWords] ^= mixed * ParamMult + i;
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}
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this->FinalizeInitialization();
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}
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void Initialize(const u32* seed, int seed_count) {
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this->state.data[0] = 0;
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this->state.data[1] = ParamMat1;
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this->state.data[2] = ParamMat2;
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this->state.data[3] = ParamTmat;
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{
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const int num_init_iterations = std::max(seed_count + 1, MinimumInitIterations) - 1;
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GenerateInitialValuePlus(&this->state, 0, seed_count);
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for (int i = 0; i < num_init_iterations; i++) {
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GenerateInitialValuePlus(&this->state, (i + 1) % NumStateWords,
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(i < seed_count) ? seed[i] : 0);
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}
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for (int i = 0; i < static_cast<int>(NumStateWords); i++) {
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GenerateInitialValueXor(&this->state,
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(i + 1 + num_init_iterations) % NumStateWords);
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}
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}
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this->FinalizeInitialization();
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}
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// State management.
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void GetState(TinyMT::State& out) const {
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out.data = this->state.data;
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}
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void SetState(const TinyMT::State& state_) {
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this->state.data = state_.data;
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}
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// Random generation.
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void GenerateRandomBytes(void* dst, std::size_t size) {
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const uintptr_t start = reinterpret_cast<uintptr_t>(dst);
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const uintptr_t end = start + size;
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const uintptr_t aligned_start = Common::AlignUp(start, 4);
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const uintptr_t aligned_end = Common::AlignDown(end, 4);
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// Make sure we're aligned.
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if (start < aligned_start) {
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const u32 rnd = this->GenerateRandomU32();
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std::memcpy(dst, &rnd, aligned_start - start);
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}
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// Write as many aligned u32s as we can.
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{
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u32* cur_dst = reinterpret_cast<u32*>(aligned_start);
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u32* const end_dst = reinterpret_cast<u32*>(aligned_end);
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while (cur_dst < end_dst) {
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*(cur_dst++) = this->GenerateRandomU32();
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}
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}
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// Handle any leftover unaligned data.
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if (aligned_end < end) {
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const u32 rnd = this->GenerateRandomU32();
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std::memcpy(reinterpret_cast<void*>(aligned_end), &rnd, end - aligned_end);
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}
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}
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u32 GenerateRandomU32() {
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// Advance state.
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const u32 x0 =
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(this->state.data[0] & TopBitmask) ^ this->state.data[1] ^ this->state.data[2];
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const u32 y0 = this->state.data[3];
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const u32 x1 = x0 ^ (x0 << 1);
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const u32 y1 = y0 ^ (y0 >> 1) ^ x1;
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const u32 state0 = this->state.data[1];
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u32 state1 = this->state.data[2];
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u32 state2 = x1 ^ (y1 << 10);
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const u32 state3 = y1;
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if ((y1 & 1) != 0) {
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state1 ^= ParamMat1;
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state2 ^= ParamMat2;
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}
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this->state.data[0] = state0;
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this->state.data[1] = state1;
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this->state.data[2] = state2;
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this->state.data[3] = state3;
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// Temper.
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const u32 t1 = state0 + (state2 >> 8);
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u32 t0 = state3 ^ t1;
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if ((t1 & 1) != 0) {
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t0 ^= ParamTmat;
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}
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return t0;
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}
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u64 GenerateRandomU64() {
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const u32 lo = this->GenerateRandomU32();
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const u32 hi = this->GenerateRandomU32();
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return (u64{hi} << 32) | u64{lo};
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}
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float GenerateRandomF32() {
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// Floats have 24 bits of mantissa.
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constexpr u32 MantissaBits = 24;
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return static_cast<float>(GenerateRandomU24()) * (1.0f / (1U << MantissaBits));
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}
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double GenerateRandomF64() {
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// Doubles have 53 bits of mantissa.
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// The smart way to generate 53 bits of random would be to use 32 bits
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// from the first rnd32() call, and then 21 from the second.
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// Nintendo does not. They use (32 - 5) = 27 bits from the first rnd32()
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// call, and (32 - 6) bits from the second. We'll do what they do, but
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// There's not a clear reason why.
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constexpr u32 MantissaBits = 53;
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constexpr u32 Shift1st = (64 - MantissaBits) / 2;
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constexpr u32 Shift2nd = (64 - MantissaBits) - Shift1st;
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const u32 first = (this->GenerateRandomU32() >> Shift1st);
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const u32 second = (this->GenerateRandomU32() >> Shift2nd);
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return (1.0 * first * (u64{1} << (32 - Shift2nd)) + second) *
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(1.0 / (u64{1} << MantissaBits));
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}
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};
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} // namespace Common
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