fix bug in bytes.Map and add test cases for Map in both strings and bytes packages.

thanks to ulrik.sverdrup for the test case.

Fixes #191.

R=rsc
CC=golang-dev
https://golang.org/cl/155056

src/pkg/bytes/bytes.go

@@ -220,9 +220,7 @@ func Map(mapping func(rune int) int, s []byte) []byte {
 	for i := 0; i < len(s); {
 		wid := 1;
 		rune := int(s[i]);
-		if rune < utf8.RuneSelf {
-			rune = mapping(rune)
-		} else {
+		if rune >= utf8.RuneSelf {
 			rune, wid = utf8.DecodeRune(s[i:len(s)])
 		}
 		rune = mapping(rune);

src/pkg/bytes/bytes_test.go

@@ -268,9 +268,22 @@ func tenRunes(rune int) string {
 	return string(r);
 }
 
+// User-defined self-inverse mapping function
+func rot13(rune int) int {
+	step := 13;
+	if rune >= 'a' && rune <= 'z' {
+		return ((rune - 'a' + step) % 26) + 'a'
+	}
+	if rune >= 'A' && rune <= 'Z' {
+		return ((rune - 'A' + step) % 26) + 'A'
+	}
+	return rune;
+}
+
 func TestMap(t *testing.T) {
 	// Run a couple of awful growth/shrinkage tests
 	a := tenRunes('a');
+
 	// 1.  Grow.  This triggers two reallocations in Map.
 	maxRune := func(rune int) int { return unicode.MaxRune };
 	m := Map(maxRune, Bytes(a));
@@ -278,6 +291,7 @@ func TestMap(t *testing.T) {
 	if string(m) != expect {
 		t.Errorf("growing: expected %q got %q", expect, m)
 	}
+
 	// 2. Shrink
 	minRune := func(rune int) int { return 'a' };
 	m = Map(minRune, Bytes(tenRunes(unicode.MaxRune)));
@@ -285,6 +299,20 @@ func TestMap(t *testing.T) {
 	if string(m) != expect {
 		t.Errorf("shrinking: expected %q got %q", expect, m)
 	}
+
+	// 3. Rot13
+	m = Map(rot13, Bytes("a to zed"));
+	expect = "n gb mrq";
+	if string(m) != expect {
+		t.Errorf("rot13: expected %q got %q", expect, m)
+	}
+
+	// 4. Rot13^2
+	m = Map(rot13, Map(rot13, Bytes("a to zed")));
+	expect = "a to zed";
+	if string(m) != expect {
+		t.Errorf("rot13: expected %q got %q", expect, m)
+	}
 }
 
 func TestToUpper(t *testing.T)	{ runStringTests(t, ToUpper, "ToUpper", upperTests) }

src/pkg/strings/strings_test.go

@@ -226,6 +226,18 @@ func tenRunes(rune int) string {
 	return string(r);
 }
 
+// User-defined self-inverse mapping function
+func rot13(rune int) int {
+	step := 13;
+	if rune >= 'a' && rune <= 'z' {
+		return ((rune - 'a' + step) % 26) + 'a'
+	}
+	if rune >= 'A' && rune <= 'Z' {
+		return ((rune - 'A' + step) % 26) + 'A'
+	}
+	return rune;
+}
+
 func TestMap(t *testing.T) {
 	// Run a couple of awful growth/shrinkage tests
 	a := tenRunes('a');
@@ -236,6 +248,7 @@ func TestMap(t *testing.T) {
 	if m != expect {
 		t.Errorf("growing: expected %q got %q", expect, m)
 	}
+
 	// 2. Shrink
 	minRune := func(rune int) int { return 'a' };
 	m = Map(minRune, tenRunes(unicode.MaxRune));
@@ -243,6 +256,20 @@ func TestMap(t *testing.T) {
 	if m != expect {
 		t.Errorf("shrinking: expected %q got %q", expect, m)
 	}
+
+	// 3. Rot13
+	m = Map(rot13, "a to zed");
+	expect = "n gb mrq";
+	if m != expect {
+		t.Errorf("rot13: expected %q got %q", expect, m)
+	}
+
+	// 4. Rot13^2
+	m = Map(rot13, Map(rot13, "a to zed"));
+	expect = "a to zed";
+	if m != expect {
+		t.Errorf("rot13: expected %q got %q", expect, m)
+	}
 }
 
 func TestToUpper(t *testing.T)	{ runStringTests(t, ToUpper, "ToUpper", upperTests) }