[lib/util] Add Strings.asciiLt

lib/util/Strings.v3

@@ -153,4 +153,16 @@ component Strings {
 	def puts(s: string) -> StringBuilder -> StringBuilder {
 		return StringBuilder.puts(_, s);
 	}
+	// Compares two strings according to 8-bit ASCII lexicographical order.
+	def asciiLt(a: string, b: string) -> bool {
+		if (a == null) return b != null; // null < non-null
+		if (b == null) return false;     // non-null > null
+		for (i < a.length) {
+			if (i >= b.length) return false;
+			var ac = a[i], bc = b[i];
+			if (ac < bc) return true;
+			if (bc < ac) return false;
+		}
+		return a.length < b.length;
+	}
 }

test/lib/StringsTest.v3

@@ -6,6 +6,7 @@ def X = [
 	T("parseLiteral", test_parseLiteral),
 	T("parseLiteralHex", test_parseLiteralHex),
 	T("parseLiteralErr", test_parseLiteralErr),
+	T("asciiLt", test_asciiLt),
 	()
 ];
 
@@ -89,3 +90,26 @@ def test_parseLiteralErr(t: LibTest) {
 	}
 
 }
+
+def test_asciiLt(t: LibTest) {
+	def empty = "", a = "a", b = "b", aa = "aa", bb = "bb";
+	def LT = Strings.asciiLt;
+
+	t.assertz(false, LT(null,  null));
+	t.assertz(true,  LT(null,  empty));
+	t.assertz(false, LT(empty, null));
+	t.assertz(false, LT(empty, empty));
+
+	t.assertz(false, LT(a, a));
+	t.assertz(true,  LT(a, b));
+	t.assertz(false, LT(b, a));
+	t.assertz(false, LT(b, b));
+
+	t.assertz(false, LT(aa, a));
+	t.assertz(true,  LT(a, aa));
+	t.assertz(false, LT(b, aa));
+	t.assertz(true,  LT(aa, b));
+
+	t.assertz(true,  LT("aaaaaa", "aazaaa"));
+	t.assertz(false, LT("BBBBBB", "BBABBB"));
+}

test/lib/main.v3

@@ -35,6 +35,9 @@ class LibTest(prefix: string, name: string, fun: LibTest -> void, tail: LibTest)
 	def assert(z: bool) -> this {
 		if (!z) fail("expected true");
 	}
+	def assertz(expected: bool, got: bool) -> this {
+		if (expected != got) fail(if(expected, "expected true", "expected false"));
+	}
 	def asserteq<T>(a: T, b: T) -> this {
 		if (a != b) fail("expected equal");
 	}