ｗ

tests/pixel-contract.mjs

@@ -0,0 +1,62 @@
+import '../kernels.js';
+
+const K = globalThis.MANDEL_KERNELS;
+const decode = b64 => Uint8Array.from(atob(b64), c => c.charCodeAt(0));
+
+function instantiate() {
+  for (const [name, payload] of [['simd', K.WASM_SIMD_B64], ['scalar', K.WASM_SCALAR_B64]]) {
+    try {
+      const instance = new WebAssembly.Instance(new WebAssembly.Module(decode(payload)), {});
+      return { name, ex: instance.exports };
+    } catch {}
+  }
+  throw new Error('Neither shallow WASM backend could be instantiated.');
+}
+
+function jsPixel(cre, cim, span, width, height, x, y, iter) {
+  const scale = span / width;
+  // Match the public ABI operation order: JavaScript shifts the center once,
+  // then the kernel applies the historical integer-grid formula.  The
+  // algebraically equivalent single expression can round differently at a
+  // chaotic boundary and is not a useful backend-equivalence oracle.
+  const shiftedRe = cre + scale * 0.5;
+  const shiftedIm = cim - scale * 0.5;
+  const cr = shiftedRe + scale * (x - width * 0.5);
+  const ci = shiftedIm + scale * (height * 0.5 - y);
+  let zr = 0, zi = 0, zr2 = 0, zi2 = 0, n = 0;
+  while (n < iter && zr2 + zi2 <= 4) {
+    zi = 2 * zr * zi + ci;
+    zr = zr2 - zi2 + cr;
+    zr2 = zr * zr;
+    zi2 = zi * zi;
+    n++;
+  }
+  return n;
+}
+
+const backend = instantiate();
+const scenes = [
+  { cre: -0.5, cim: 0, span: 3.4, width: 31, height: 19, iter: 350 },
+  { cre: -0.743643887037151, cim: 0.13182590420533, span: 4e-4, width: 37, height: 23, iter: 700 }
+];
+
+let samples = 0;
+let mismatches = 0;
+const mismatchDetails = [];
+for (const s of scenes) {
+  const scale = s.span / s.width;
+  const npx = backend.ex.render_rows(s.cre + scale * 0.5, s.cim - scale * 0.5, s.span, s.width, s.height, 0, s.height, s.iter);
+  const counts = new Uint32Array(backend.ex.memory.buffer, backend.ex.counts_ptr(), npx);
+  for (let y = 0; y < s.height; y++) for (let x = 0; x < s.width; x++) {
+    samples++;
+    const wasmCount = counts[y * s.width + x];
+    const jsCount = jsPixel(s.cre, s.cim, s.span, s.width, s.height, x, y, s.iter);
+    if (wasmCount !== jsCount) {
+      mismatches++;
+      if (mismatchDetails.length < 12) mismatchDetails.push({ scene: scenes.indexOf(s), x, y, wasmCount, jsCount });
+    }
+  }
+}
+
+if (mismatches) throw new Error(`Pixel contract mismatch: ${mismatches}/${samples} ${JSON.stringify(mismatchDetails)}`);
+console.log(JSON.stringify({ status: 'pass', backend: backend.name, samples, mismatches, contract: '(x+0.5,y+0.5)' }));