wehub-resource-sync
105 lines
3.2 KiB
C#
105 lines
3.2 KiB
C#
using T3.Core.Utils;
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namespace Lib.numbers.@int.basic;
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[Guid("74901305-773d-4246-b962-2478096159b7")]
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internal sealed class RandomChoiceIndex : Instance<RandomChoiceIndex>
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{
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[Output(Guid = "8509fd5c-8314-4f6e-906f-5bae82dfeace")]
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public readonly Slot<int> Result = new();
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public RandomChoiceIndex()
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{
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Result.UpdateAction += Update;
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}
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/// <summary>
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/// Avoiding duplicates in a deterministic random shuffle index is more complicated
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/// than you might think
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///
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/// This algorithm uses a fixed length random slice buffer.
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/// If the current random index in outside the current range of the that buffer,
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/// it is initialized with non-repeating numbers. To resolve the duplications
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/// between the end of that buffer and the next one, we walk backwards and flip
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/// new numbers until the double is resolved.
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/// </summary>
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private void Update(EvaluationContext context)
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{
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var n = Value.GetValue(context);
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var modulo = Mod.GetValue(context);
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if (modulo < 2)
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{
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Result.Value = 0;
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return;
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}
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if (modulo == 2)
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{
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Result.Value = n.Mod(2);
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return;
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}
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if (!_initialized
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|| n < _lastBufferIndex
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|| n >= _lastBufferIndex + ModBufferLength
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|| modulo != _modulo)
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{
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_modulo = modulo;
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var bufferStartIndex = n - n.Mod(ModBufferLength) - ModBufferLength/4; // counting backwards more unlikely
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FillBuffer(bufferStartIndex, modulo);
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_lastBufferIndex = bufferStartIndex;
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_initialized = true;
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}
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var rand = _buffer[n.Mod(ModBufferLength)];
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Result.Value = rand;
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}
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private int _lastBufferIndex = -1;
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private bool _initialized;
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private int _modulo = -1;
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private void FillBuffer(int startIndex, int modulo)
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{
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// Initial value
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var value = MathUtils.XxHash(startIndex).Mod(modulo);
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_buffer[0] = value;
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// Fill the rest of the buffer
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for (var i = 1; i < ModBufferLength; i++)
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{
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// Use modulo - 1 and add 1 to avoid repetition
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var offset = MathUtils.XxHash(startIndex + i).Mod(modulo - 1) + 1;
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value = (value + offset).Mod(modulo);
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_buffer[i] = value;
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}
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// Fix potential collision with the next sequence start
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var expectedNext = MathUtils.XxHash(startIndex + ModBufferLength).Mod(modulo);
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for (var i = ModBufferLength - 1; i > 0; i--)
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{
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if (_buffer[i] != expectedNext)
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break;
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var offset = MathUtils.XxHash(startIndex + i + 13331).Mod(modulo - 1) + 1;
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var newValue = (expectedNext + offset).Mod(modulo);
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_buffer[i] = newValue;
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expectedNext = newValue;
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}
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}
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private const int ModBufferLength = 100; // balance cost of buffer init with memory
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private readonly int[] _buffer = new int[ModBufferLength];
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[Input(Guid = "b84a35a2-8eb9-45a2-ae68-bfce77fc1616")]
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public readonly InputSlot<int> Value = new();
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[Input(Guid = "009e80fa-7f42-4db6-abd8-91039602bed6")]
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public readonly InputSlot<int> Mod = new();
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} |