LibHac/tests/LibHac.Tests/Random.cs

using System;
using System.Numerics;
using System.Runtime.InteropServices;

namespace LibHac.Tests;

public struct Random
{
    private ulong _state1;
    private ulong _state2;

    public Random(ulong seed)
    {
        unchecked
        {
            ulong x = seed;
            ulong z = x + 0x9e3779b97f4a7c15;
            z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
            z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
            x = z ^ (z >> 31);
            z = (x += 0x9e3779b97f4a7c15);
            z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
            z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
            _state1 = z ^ (z >> 31);
            _state2 = x;
        }
    }

    ulong Next()
    {
        ulong s0 = _state1;
        ulong s1 = _state2;
        ulong result = unchecked(BitOperations.RotateLeft(s0 + s1, 17) + s0);

        s1 ^= s0;
        _state1 = BitOperations.RotateLeft(s0, 49) ^ s1 ^ (s1 << 21);
        _state2 = BitOperations.RotateLeft(s1, 28);

        return result;
    }

    public int Next(int minValue, int maxValue)
    {
        if (minValue > maxValue)
        {
            throw new ArgumentOutOfRangeException(nameof(minValue));
        }

        unchecked
        {
            long range = (long)maxValue - minValue;
            return (int)((uint)Next() * (1.0 / uint.MaxValue) * range) + minValue;
        }
    }

    public void NextBytes(Span<byte> buffer)
    {
        Span<ulong> bufferUlong = MemoryMarshal.Cast<byte, ulong>(buffer);

        for (int i = 0; i < bufferUlong.Length; i++)
        {
            bufferUlong[i] = Next();
        }

        for (int i = bufferUlong.Length * sizeof(ulong); i < buffer.Length; i++)
        {
            buffer[i] = unchecked((byte)Next());
        }
    }
}