strings: speed up byteReplacer.Replace

benchmark                         old ns/op    new ns/op    delta
BenchmarkByteReplacerWriteString       7359         3661  -50.25%

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://golang.org/cl/102550043

1 files changed, 10 insertions, 1 deletions

diff --git a/src/pkg/strings/replace_test.go b/src/pkg/strings/replace_test.go
index ca57f08251..2cb318b69d 100644
--- a/src/pkg/strings/replace_test.go
+++ b/src/pkg/strings/replace_test.go
@@ -480,7 +480,7 @@ func BenchmarkHTMLEscapeOld(b *testing.B) {
 	}
 }
 
-func BenchmarkWriteString(b *testing.B) {
+func BenchmarkByteStringReplacerWriteString(b *testing.B) {
 	str := Repeat("I <3 to escape HTML & other text too.", 100)
 	buf := new(bytes.Buffer)
 	for i := 0; i < b.N; i++ {
@@ -489,6 +489,15 @@ func BenchmarkWriteString(b *testing.B) {
 	}
 }
 
+func BenchmarkByteReplacerWriteString(b *testing.B) {
+	str := Repeat("abcdefghijklmnopqrstuvwxyz", 100)
+	buf := new(bytes.Buffer)
+	for i := 0; i < b.N; i++ {
+		capitalLetters.WriteString(buf, str)
+		buf.Reset()
+	}
+}
+
 // BenchmarkByteByteReplaces compares byteByteImpl against multiple Replaces.
 func BenchmarkByteByteReplaces(b *testing.B) {
 	str := Repeat("a", 100) + Repeat("b", 100)