src/Godosa.Core/Runs/SeedStreams.cs


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namespace Godosa.Core.Runs;

/// <summary>Independent per-purpose seeds from one run seed: SplitMix64 output number <c>stream + 1</c> of
/// <paramref name="seed"/> (audio draws then never shift the game's stream).</summary>
public static class SeedStreams
{
    public static ulong Of(ulong seed, int stream)
    {
        var z = unchecked(seed + (ulong)(stream + 1) * 0x9E3779B97F4A7C15UL);
        z = unchecked((z ^ (z >> 30)) * 0xBF58476D1CE4E5B9UL);
        z = unchecked((z ^ (z >> 27)) * 0x94D049BB133111EBUL);
        return z ^ (z >> 31);
    }
}