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>
diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
index 60de451..b868240 100644
--- a/src/bytes/bytes.go
+++ b/src/bytes/bytes.go
@@ -138,6 +138,16 @@
return -1
}
+// LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
+func LastIndexByte(s []byte, c byte) int {
+ for i := len(s) - 1; i >= 0; i-- {
+ if s[i] == c {
+ return i
+ }
+ }
+ return -1
+}
+
// IndexRune interprets s as a sequence of UTF-8-encoded Unicode code points.
// It returns the byte index of the first occurrence in s of the given rune.
// It returns -1 if rune is not present in s.
diff --git a/src/bytes/bytes_test.go b/src/bytes/bytes_test.go
index 980c41d..6245e48 100644
--- a/src/bytes/bytes_test.go
+++ b/src/bytes/bytes_test.go
@@ -265,6 +265,23 @@
}
}
+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
diff --git a/src/strings/strings.go b/src/strings/strings.go
index c6085f5..7b8a6b5 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -271,6 +271,16 @@
return -1
}
+// LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
+func LastIndexByte(s string, c byte) int {
+ for i := len(s) - 1; i >= 0; i-- {
+ if s[i] == c {
+ return i
+ }
+ }
+ return -1
+}
+
// Generic split: splits after each instance of sep,
// including sepSave bytes of sep in the subarrays.
func genSplit(s, sep string, sepSave, n int) []string {
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index ee0c260..4e21dea 100644
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -120,6 +120,23 @@
func TestIndexAny(t *testing.T) { runIndexTests(t, IndexAny, "IndexAny", indexAnyTests) }
func TestLastIndexAny(t *testing.T) { runIndexTests(t, LastIndexAny, "LastIndexAny", lastIndexAnyTests) }
+func TestLastIndexByte(t *testing.T) {
+ testCases := []IndexTest{
+ {"", "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(test.s, test.sep[0])
+ if actual != test.out {
+ t.Errorf("LastIndexByte(%q,%c) = %v; want %v", test.s, test.sep[0], actual, test.out)
+ }
+ }
+}
+
var indexRuneTests = []struct {
s string
rune rune
