core/src/Random.cpp

#include "core/Random.hpp"

#include <cstring>

using Core::Random;

Random::Random(u32 seed) : data(), index(0) {
    for(u32& u : data) {
        u = seed;
        seed = seed * 7 + 31;
    }
}

void Random::update() {
    constexpr int M = 7;
    static const u32 map[2] = {0, 0x8EBF'D028};
    for(size_t i = 0; i < data.getLength() - M; i++) {
        data[i] = data[i + M] ^ (data[i] >> 1) ^ map[data[i] & 1];
    }
    for(size_t i = data.getLength() - M; i < data.getLength(); i++) {
        data[i] = data[i + (M - data.getLength())] ^ (data[i] >> 1) ^
                  map[data[i] & 1];
    }
    index = 0;
}

u32 Random::nextU32() {
    if(index >= data.getLength()) {
        update();
    }
    u32 u = data[index++];
    u ^= (u << 7) & 0x2B5B'2500;
    u ^= (u << 15) & 0xDB8B'0000;
    u ^= (u >> 16);
    return u;
}

template<typename T>
T limit(T value, T min, T exclusiveMax) {
    return min + value % (exclusiveMax - min);
}

u32 Random::nextU32(u32 min, u32 exclusiveMax) {
    return limit(nextU32(), min, exclusiveMax);
}

i32 Random::nextI32(i32 min, i32 exclusiveMax) {
    return limit(static_cast<i32>(nextU32() >> 1), min, exclusiveMax);
}

size_t Core::Random::nextSize(size_t min, size_t exclusiveMax) {
    return limit<size_t>(nextU32(), min, exclusiveMax);
}

bool Core::Random::nextBool() {
    return nextU32() & 1;
}

float Core::Random::nextFloat() {
    float f = static_cast<float>(nextU32()) / static_cast<float>(0xFFFF'FFFFu);
    return f >= 1.0f ? nextFloat() : f;
}