Fix and refactor indexOfDiff

Zhenming-Lin · Zhenming-Lin · commit b3ad9d8dadd8 · 2025-06-09T11:34:54.000+08:00
diff --git a/lib/std/mem.zig b/lib/std/mem.zig
@@ -844,7 +844,8 @@ fn indexOfDiffBytes(a: []const u8, b: []const u8) ?usize {
                     return mask != 0;
                 }
                 inline fn firstDiff(mask: Mask) usize {
-                    return @ctz(mask);
+                    // Endian-aware
+                    return if (native_endian == .little) @ctz(mask) else @clz(mask);
                 }
             } else struct { // SWAR path
                 const size = @sizeOf(usize);

Original file line number	Diff line number	Diff line change
`@@ -844,7 +844,8 @@ fn indexOfDiffBytes(a: []const u8, b: []const u8) ?usize {`
`844`	`844`	`return mask != 0;`
`845`	`845`	`}`
`846`	`846`	`inline fn firstDiff(mask: Mask) usize {`
`847`		`- return @ctz(mask);`
	`847`	`+ // Endian-aware`
	`848`	`+ return if (native_endian == .little) @ctz(mask) else @clz(mask);`
`848`	`849`	`}`
`849`	`850`	`} else struct { // SWAR path`
`850`	`851`	`const size = @sizeOf(usize);`