Livt.ML

src/activation/SiLUApprox.lvt

namespace Livt.ML.Activation

/**
 * Applies a fixed 8-element integer SiLU approximation using a sigmoid table.
 */
component SiLUApprox
{
	// Number of integer activations processed by Compute.
	public const VECTOR_SIZE: int = 8

	// Number of entries in the clamped sigmoid lookup table.
	public const LUT_SIZE: int = 16

	// Fixed-point scale used for sigmoid table values.
	public const SCALE_FACTOR: int = 256

	// Owned approximation table in the component numeric scale.
	sigLut: int[16]

	// Latest computed result, retained for the caller.
	output: int[8]

	/**
	 * Initializes the 16-entry sigmoid approximation table.
	 */
	new()
	{
		sigLut[0] = 128
		sigLut[1] = 187
		sigLut[2] = 225
		sigLut[3] = 244
		sigLut[4] = 251
		sigLut[5] = 254
		sigLut[6] = 255
		sigLut[7] = 255
		sigLut[8] = 255
		sigLut[9] = 255
		sigLut[10] = 255
		sigLut[11] = 255
		sigLut[12] = 255
		sigLut[13] = 255
		sigLut[14] = 255
		sigLut[15] = 255
	}

	/**
	 * Computes input * sigmoid(input) for each element and stores the outputs.
	 */
	public fn Compute(input: int[8])
	{
		for (var i = 0; i < VECTOR_SIZE; i++) {
			var clamped = input[i]

			if (clamped < 0) {
				clamped = 0
			}

			if (clamped > 15) {
				clamped = 15
			}

			var sig = sigLut[clamped]
			output[i] = input[i] * sig / SCALE_FACTOR
		}
	}

	/**
	 * Returns one computed output element, or zero when index is out of range.
	 */
	public fn GetOutput(index: int) int
	{
		if (index < 0) {
			return 0
		}

		if (index >= VECTOR_SIZE) {
			return 0
		}

		return output[index]
	}
}