encoding/csv: optimize Write by giving fieldNeedsQuotes a fast path for when Comma is ascii

name     old time/op  new time/op  delta
Write-4  2.37µs ±20%  1.90µs ±19%  -19.54%  (p=0.015 n=6+6)

Change-Id: Iadfd9a43c958704c49ceb540b44d145220f9a72f
GitHub-Last-Rev: e7d8b0bd69870a24fdd800401d721e4c5bda7750
GitHub-Pull-Request: golang/go#34507
Reviewed-on: https://go-review.googlesource.com/c/go/+/197078
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/encoding/csv/writer_test.go b/src/encoding/csv/writer_test.go
index 011f01c172..ab28b0d7c3 100644
--- a/src/encoding/csv/writer_test.go
+++ b/src/encoding/csv/writer_test.go
@@ -93,3 +93,20 @@ func TestError(t *testing.T) {
 		t.Error("Error should not be nil")
 	}
 }
+
+var benchmarkWriteData = [][]string{
+	{"abc", "def", "12356", "1234567890987654311234432141542132"},
+	{"abc", "def", "12356", "1234567890987654311234432141542132"},
+	{"abc", "def", "12356", "1234567890987654311234432141542132"},
+}
+
+func BenchmarkWrite(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		w := NewWriter(&bytes.Buffer{})
+		err := w.WriteAll(benchmarkWriteData)
+		if err != nil {
+			b.Fatal(err)
+		}
+		w.Flush()
+	}
+}