Apply restrict optimizations to ImagingQuantize's output loop

Tests/benchmarks.py

@@ -818,12 +818,27 @@ def test_font_getmask(bench: BenchmarkFixture, mode: str) -> None:
 
 
 @pytest.mark.benchmark(group="quantize")
-@pytest.mark.parametrize("mode", [m for m in MODES if m in ("L", "RGB", "RGBA")])
+@pytest.mark.parametrize(
+    "mode, method",
+    [
+        ("L", Image.Quantize.MEDIANCUT),
+        ("L", Image.Quantize.MAXCOVERAGE),
+        ("RGB", Image.Quantize.MEDIANCUT),
+        ("RGB", Image.Quantize.MAXCOVERAGE),
+        ("RGBA", Image.Quantize.FASTOCTREE),
+    ],
+    ids=lambda p: getattr(p, "name", p),
+)
 @pytest.mark.parametrize("size", SIZES, ids=_format_size)
-def test_quantize(bench: BenchmarkFixture, mode: str, size: tuple[int, int]) -> None:
+def test_quantize(
+    bench: BenchmarkFixture,
+    mode: str,
+    method: Image.Quantize,
+    size: tuple[int, int],
+) -> None:
     im = make_pillow_image(mode, size)
-    bench.extra_info["label"] = [f"quantize {mode}"]
-    result = bench(im.quantize, 256)
+    bench.extra_info["label"] = [f"quantize {mode} {method.name}"]
+    result = bench(im.quantize, 256, method=method)
     assert result.mode == "P"
 
 

src/libImaging/Quant.c

@@ -1831,10 +1831,15 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         }
         ImagingSectionEnter(&cookie);
 
+        // restrict safe: imOut is a fresh allocation and
+        //                newData was just allocated by the quantizer.
         for (i = y = 0; y < ysize; y++) {
+            UINT8 *restrict out = imOut->image8[y];
+            const uint32_t *restrict in = newData + i;
             for (x = 0; x < xsize; x++) {
-                imOut->image8[y][x] = (unsigned char)newData[i++];
+                out[x] = (UINT8)in[x];
             }
+            i += xsize;
         }
 
         free(newData);