AnyPS5/core/libs/prx/libc/src/Random.cpp

#include "prx/libc/include/general/VabiMacros.hpp"
#include <array>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <mutex>
#include <stdexcept>

namespace {

constexpr int MaxTypes = 5;
constexpr int LinearCongruentialType = 0;
constexpr int LinearCongruentialShuffles = 50;
constexpr std::array<std::int64_t, MaxTypes> MinimumStateBytes {8, 32, 64, 128, 256};
constexpr std::array<int, MaxTypes> Degrees {0, 7, 15, 31, 63};
constexpr std::array<int, MaxTypes> Separations {0, 3, 1, 3, 1};

std::uint32_t g_defaultTable[] {
    3,
    0x2cf41758, 0x27bb3711, 0x4916d4d1, 0x7b02f59f, 0x9b8e28eb, 0xc0e80269,
    0x696f5c16, 0x878f1ff5, 0x52d9c07f, 0x916a06cd, 0xb50b3a20, 0x2776970a,
    0xee4eb2a6, 0xe94640ec, 0xb1d65612, 0x9d1ed968, 0x1043f6b7, 0xa3432a76,
    0x17eacbb9, 0x3c09e2eb, 0x04f8c2b3, 0x708a1f57, 0xee341814, 0x95d0e4d2,
    0xb06f216c, 0x8bd2e72e, 0x8f7c38d7, 0xcfc6a8fc, 0x02a59495, 0xa20d2a69,
    0xe29d12d1
};

struct AdditiveFeedbackState {
    char* table;
    int type;
    int degree;
    int separation;
    int front;
    int rear;
};

std::mutex g_randomLock;
AdditiveFeedbackState g_random {reinterpret_cast<char*>(g_defaultTable), 3, 31, 3, 3, 0};

std::uint32_t LoadWord(const char* table, int index) {
    std::uint32_t value;
    std::memcpy(&value, table + sizeof(value) * static_cast<std::size_t>(index), sizeof(value));
    return value;
}

void StoreWord(char* table, int index, std::uint32_t value) {
    std::memcpy(table + sizeof(value) * static_cast<std::size_t>(index), &value, sizeof(value));
}

std::uint32_t GoodRand(std::uint32_t context) {
    std::int32_t x = static_cast<std::int32_t>(context % 0x7ffffffeu) + 1;
    const std::int32_t high = x / 127773;
    const std::int32_t low = x % 127773;
    x = 16807 * low - 2836 * high;
    if (x < 0) x += 0x7fffffff;
    return static_cast<std::uint32_t>(x - 1);
}

std::uint32_t NextLocked() {
    auto& state = g_random;
    if (state.type == LinearCongruentialType) {
        const std::uint32_t value = GoodRand(LoadWord(state.table, 1));
        StoreWord(state.table, 1, value);
        return value;
    }
    const std::uint32_t sum = LoadWord(state.table, 1 + state.front) + LoadWord(state.table, 1 + state.rear);
    StoreWord(state.table, 1 + state.front, sum);
    if (++state.front >= state.degree) {
        state.front = 0;
        ++state.rear;
    } else if (++state.rear >= state.degree) {
        state.rear = 0;
    }
    return sum >> 1;
}

void SeedLocked(std::uint32_t seed) {
    auto& state = g_random;
    StoreWord(state.table, 1, seed);
    int rounds = LinearCongruentialShuffles;
    if (state.type != LinearCongruentialType) {
        for (int i = 1; i < state.degree; ++i) StoreWord(state.table, 1 + i, GoodRand(LoadWord(state.table, i)));
        state.front = state.separation;
        state.rear = 0;
        rounds = 10 * state.degree;
    }
    for (int i = 0; i < rounds; ++i) NextLocked();
}

void SaveTypeWordLocked() {
    const auto& state = g_random;
    const int word = state.type == LinearCongruentialType ? state.type : MaxTypes * state.rear + state.type;
    StoreWord(state.table, 0, static_cast<std::uint32_t>(word));
}

}

extern "C" {

std::int64_t APS5_VABI random_nid_postfix() {
    std::lock_guard lock(g_randomLock);
    return static_cast<std::int64_t>(NextLocked());
}

void APS5_VABI srandom_nid_postfix(std::uint64_t seed) {
    std::lock_guard lock(g_randomLock);
    SeedLocked(static_cast<std::uint32_t>(seed));
}

char* APS5_VABI initstate_nid_postfix(std::uint64_t seed, char* state, std::int64_t size) {
    if (size < MinimumStateBytes[0]) return nullptr;
    if (state == nullptr) throw std::invalid_argument("initstate: null state");
    std::lock_guard lock(g_randomLock);
    char* previous = g_random.table;
    SaveTypeWordLocked();
    int type = MaxTypes - 1;
    while (size < MinimumStateBytes[static_cast<std::size_t>(type)]) --type;
    g_random = {state, type, Degrees[static_cast<std::size_t>(type)], Separations[static_cast<std::size_t>(type)], 0, 0};
    SeedLocked(static_cast<std::uint32_t>(seed));
    SaveTypeWordLocked();
    return previous;
}

char* APS5_VABI setstate_nid_postfix(char* state) {
    if (state == nullptr) throw std::invalid_argument("setstate: null state");
    std::lock_guard lock(g_randomLock);
    const std::uint32_t word = LoadWord(state, 0);
    const int type = static_cast<int>(word % MaxTypes);
    const std::uint32_t rear = word / MaxTypes;
    const int degree = Degrees[static_cast<std::size_t>(type)];
    if (type != LinearCongruentialType && rear >= static_cast<std::uint32_t>(degree)) return nullptr;
    char* previous = g_random.table;
    SaveTypeWordLocked();
    const int separation = Separations[static_cast<std::size_t>(type)];
    g_random.table = state;
    g_random.type = type;
    g_random.degree = degree;
    g_random.separation = separation;
    if (type != LinearCongruentialType) {
        g_random.rear = static_cast<int>(rear);
        g_random.front = (static_cast<int>(rear) + separation) % degree;
    }
    return previous;
}

}