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/strings/strings.go b/src/strings/strings.go
index 02c032046b..7d3ed37edd 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -8,6 +8,7 @@
 package strings
 
 import (
+	"internal/bytealg"
 	"unicode"
 	"unicode/utf8"
 )
@@ -72,12 +73,16 @@ func hashStrRev(sep string) (uint32, uint32) {
 	return hash, pow
 }
 
-// countGeneric implements Count.
-func countGeneric(s, substr string) int {
+// Count counts the number of non-overlapping instances of substr in s.
+// If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
+func Count(s, substr string) int {
 	// special case
 	if len(substr) == 0 {
 		return utf8.RuneCountInString(s) + 1
 	}
+	if len(substr) == 1 {
+		return bytealg.CountString(s, substr[0])
+	}
 	n := 0
 	for {
 		i := Index(s, substr)