asmhatre/vector-api-jep-537-demo
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Add image brightness + clamp kernel

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asmhatre
2026-07-26 11:46:16 +00:00
parent db213647d1
commit 19405ef9e4
1 changed files with 51 additions and 0 deletions
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timings/src/main/java/com/ankurm/vectorapi/Brightness.java Normal file
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package com.ankurm.vectorapi;
import jdk.incubator.vector.*;
/** Image brightness: scale, bias, clamp to [0, 255]. The clamp is two branches. */
public final class Brightness {
static final VectorSpecies<Float> SP = FloatVector.SPECIES_PREFERRED;
// Scalar: the clamp is two data-dependent branches
static void brightScalar(float[] in, float[] out, float gain, float bias) {
for (int i = 0; i < in.length; i++) {
float v = in[i] * gain + bias;
if (v < 0f) v = 0f; else if (v > 255f) v = 255f;
out[i] = v;
}
}
static void brightVector(float[] in, float[] out, float gain, float bias) {
var vg = FloatVector.broadcast(SP, gain);
var vb = FloatVector.broadcast(SP, bias);
var lo = FloatVector.zero(SP);
var hi = FloatVector.broadcast(SP, 255f);
int i = 0, bound = SP.loopBound(in.length);
for (; i < bound; i += SP.length()) {
FloatVector.fromArray(SP, in, i).fma(vg, vb).max(lo).min(hi).intoArray(out, i);
}
for (; i < in.length; i++) { // scalar tail
float v = in[i] * gain + bias;
if (v < 0f) v = 0f; else if (v > 255f) v = 255f;
out[i] = v;
}
}
static void run(int n) {
float[] in = Data.randomFloats(n, 4);
for (int i = 0; i < n; i++) in[i] = in[i] * 300f - 20f; // some pixels clamp at both ends
float[] o1 = new float[n], o2 = new float[n];
brightScalar(in, o1, 1.4f, 12f);
brightVector(in, o2, 1.4f, 12f);
Data.assertSame("brightness", o1, o2);
System.out.println("--- kernel 3: image brightness + clamp, " + n + " pixels ---");
double s = Bench.measure("scalar (branchy clamp)", () -> brightScalar(in, o1, 1.4f, 12f));
double v = Bench.measure("Vector API (max/min)", () -> brightVector(in, o2, 1.4f, 12f));
Bench.speedup("vector advantage", s, v);
System.out.println();
}
private Brightness() {}
}