internal/bytealg: move Count to bytealg

Move bytes.Count and strings.Count to bytealg.

Update #19792

Change-Id: I3e4e14b504a0b71758885bb131e5656e342cf8cb
Reviewed-on: https://go-review.googlesource.com/98495
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
index 9af177fa88..08d8260e9e 100644
--- a/src/bytes/bytes.go
+++ b/src/bytes/bytes.go
@@ -7,6 +7,7 @@
 package bytes
 
 import (
+	"internal/bytealg"
 	"unicode"
 	"unicode/utf8"
 )
@@ -46,12 +47,16 @@ func explode(s []byte, n int) [][]byte {
 	return a[0:na]
 }
 
-// countGeneric actually implements Count
-func countGeneric(s, sep []byte) int {
+// Count counts the number of non-overlapping instances of sep in s.
+// If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.
+func Count(s, sep []byte) int {
 	// special case
 	if len(sep) == 0 {
 		return utf8.RuneCount(s) + 1
 	}
+	if len(sep) == 1 {
+		return bytealg.Count(s, sep[0])
+	}
 	n := 0
 	for {
 		i := Index(s, sep)