mirror of
https://github.com/libretro/bsnes-libretro.git
synced 2024-11-23 17:09:44 +00:00
97 lines
2.2 KiB
C++
97 lines
2.2 KiB
C++
#pragma once
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namespace Emulator {
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struct Random {
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enum class Entropy : uint { None, Low, High };
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auto operator()() -> uint64 {
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return random();
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}
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auto entropy(Entropy entropy) -> void {
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_entropy = entropy;
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seed();
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}
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auto seed(maybe<uint32> seed = nothing, maybe<uint32> sequence = nothing) -> void {
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if(!seed) seed = (uint32)clock();
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if(!sequence) sequence = 0;
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_state = 0;
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_increment = sequence() << 1 | 1;
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step();
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_state += seed();
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step();
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}
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auto random() -> uint64 {
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if(_entropy == Entropy::None) return 0;
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return (uint64)step() << 32 | (uint64)step() << 0;
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}
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auto bias(uint64 bias) -> uint64 {
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if(_entropy == Entropy::None) return bias;
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return random();
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}
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auto bound(uint64 bound) -> uint64 {
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uint64 threshold = -bound % bound;
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while(true) {
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uint64 result = random();
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if(result >= threshold) return result % bound;
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}
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}
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auto array(uint8* data, uint32 size) -> void {
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if(_entropy == Entropy::None) {
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memory::fill(data, size);
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return;
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}
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if(_entropy == Entropy::High) {
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for(uint32 address : range(size)) {
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data[address] = random();
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}
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return;
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}
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//Entropy::Low
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uint lobit = random() & 3;
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uint hibit = (lobit + 8 + (random() & 3)) & 15;
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uint lovalue = random() & 255;
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uint hivalue = random() & 255;
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if((random() & 3) == 0) lovalue = 0;
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if((random() & 1) == 0) hivalue = ~lovalue;
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for(uint32 address : range(size)) {
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uint8 value = (address & 1ull << lobit) ? lovalue : hivalue;
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if((address & 1ull << hibit)) value = ~value;
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if((random() & 511) == 0) value ^= 1 << (random() & 7);
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if((random() & 2047) == 0) value ^= 1 << (random() & 7);
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data[address] = value;
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}
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}
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auto serialize(serializer& s) -> void {
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s.integer((uint&)_entropy);
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s.integer(_state);
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s.integer(_increment);
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}
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private:
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auto step() -> uint32 {
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uint64 state = _state;
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_state = state * 6364136223846793005ull + _increment;
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uint32 xorshift = (state >> 18 ^ state) >> 27;
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uint32 rotate = state >> 59;
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return xorshift >> rotate | xorshift << (-rotate & 31);
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}
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Entropy _entropy = Entropy::High;
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uint64 _state;
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uint64 _increment;
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};
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}
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