add bytes.IndexByte; common case we can make fast later.

also pick off the special case in strings.Index.   don't want strings.IndexByte
because the call site will very rarely need to allocate and we can handle the
test in the code itself.   bytes.IndexByte can avoid a common allocation.

R=rsc
CC=golang-dev
http://codereview.appspot.com/156091

2 files changed, 27 insertions, 0 deletions

diff --git a/src/pkg/strings/strings.go b/src/pkg/strings/strings.go
index 7ccfc5ca8..fb3070a1a 100644
--- a/src/pkg/strings/strings.go
+++ b/src/pkg/strings/strings.go
@@ -56,6 +56,15 @@ func Index(s, sep string) int {
 		return 0
 	}
 	c := sep[0];
+	if n == 1 {
+		// special case worth making fast
+		for i := 0; i < len(s); i++ {
+			if s[i] == c {
+				return i
+			}
+		}
+		return -1;
+	}
 	for i := 0; i+n <= len(s); i++ {
 		if s[i] == c && (n == 1 || s[i:i+n] == sep) {
 			return i
@@ -71,6 +80,15 @@ func LastIndex(s, sep string) int {
 		return len(s)
 	}
 	c := sep[0];
+	if n == 1 {
+		// special case worth making fast
+		for i := len(s) - 1; i >= 0; i-- {
+			if s[i] == c {
+				return i
+			}
+		}
+		return -1;
+	}
 	for i := len(s) - n; i >= 0; i-- {
 		if s[i] == c && (n == 1 || s[i:i+n] == sep) {
 			return i
diff --git a/src/pkg/strings/strings_test.go b/src/pkg/strings/strings_test.go
index 0073f0d0e..1171db224 100644
--- a/src/pkg/strings/strings_test.go
+++ b/src/pkg/strings/strings_test.go
@@ -46,6 +46,14 @@ var indexTests = []IndexTest{
 	IndexTest{"foo", "", 0},
 	IndexTest{"foo", "o", 1},
 	IndexTest{"abcABCabc", "A", 3},
+	// cases with one byte strings - test special case in Index()
+	IndexTest{"", "a", -1},
+	IndexTest{"x", "a", -1},
+	IndexTest{"x", "x", 0},
+	IndexTest{"abc", "a", 0},
+	IndexTest{"abc", "b", 1},
+	IndexTest{"abc", "c", 2},
+	IndexTest{"abc", "x", -1},
 }
 
 var lastIndexTests = []IndexTest{
@@ -54,6 +62,7 @@ var lastIndexTests = []IndexTest{
 	IndexTest{"", "foo", -1},
 	IndexTest{"fo", "foo", -1},
 	IndexTest{"foo", "foo", 0},
+	IndexTest{"foo", "f", 0},
 	IndexTest{"oofofoofooo", "f", 7},
 	IndexTest{"oofofoofooo", "foo", 7},
 	IndexTest{"barfoobarfoo", "foo", 9},