bytes: make search linear and splits consistent

lib/bytes/index_test.ww

@@ -110,6 +110,27 @@ import bytes;
 	case let i: i32 => { assert(!(i != 3)); };
 	case void => abort();
 	};
+
+	// Periodic long needles exercise the two-way path's critical-period
+	// memory. The first candidate shares a long prefix and must be skipped
+	// without missing the later match; the second never matches.
+	let hp: [18]u8;
+	let np: [7]u8;
+	let i: i32 = 0;
+	for (i < 18) { hp[i] = 'a'; i += 1; };
+	hp[8] = 'b'; hp[17] = 'b';
+	i = 0;
+	for (i < 6) { np[i] = 'a'; i += 1; };
+	np[6] = 'b';
+	match (bytes.index(hp[0:18], np[0:7])) {
+	case let off: i32 => { assert(!(off != 2)); };
+	case void => abort();
+	};
+	np[6] = 'c';
+	match (bytes.index(hp[0:18], np[0:7])) {
+	case let off: i32 => abort();
+	case void => void;
+	};
 };
 
 // ref/hare/bytes/index.ha:118.