bytes, strings: add LastIndexByte

Currently the packages have the following index functions:

func Index(s, sep []byte) int
func IndexAny(s []byte, chars string) int
func IndexByte(s []byte, c byte) int
func IndexFunc(s []byte, f func(r rune) bool) int
func IndexRune(s []byte, r rune) int

func LastIndex(s, sep []byte) int
func LastIndexAny(s []byte, chars string) int
func LastIndexFunc(s []byte, f func(r rune) bool) int

Searching for the last occurrence of a byte is quite common
for string parsing algorithms (e.g. find the last paren on a line).
Also addition of LastIndexByte makes the set more orthogonal.

Change-Id: Ida168849acacf8e78dd70c1354bef9eac5effafe
Reviewed-on: https://go-review.googlesource.com/9500
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/bytes/bytes_test.go b/src/bytes/bytes_test.go
index 980c41d754..6245e48180 100644
--- a/src/bytes/bytes_test.go
+++ b/src/bytes/bytes_test.go
@@ -265,6 +265,23 @@ func TestIndexByte(t *testing.T) {
 	}
 }
 
+func TestLastIndexByte(t *testing.T) {
+	testCases := []BinOpTest{
+		{"", "q", -1},
+		{"abcdef", "q", -1},
+		{"abcdefabcdef", "a", len("abcdef")},      // something in the middle
+		{"abcdefabcdef", "f", len("abcdefabcde")}, // last byte
+		{"zabcdefabcdef", "z", 0},                 // first byte
+		{"a☺b☻c☹d", "b", len("a☺")},               // non-ascii
+	}
+	for _, test := range testCases {
+		actual := LastIndexByte([]byte(test.a), test.b[0])
+		if actual != test.i {
+			t.Errorf("LastIndexByte(%q,%c) = %v; want %v", test.a, test.b[0], actual, test.i)
+		}
+	}
+}
+
 // test a larger buffer with different sizes and alignments
 func TestIndexByteBig(t *testing.T) {
 	var n = 1024