unicode/utf16: add benchmarks

For #6957

Change-Id: Ic497c12f33efc933e9fe81f6cd1b2a0a01abbabf
Reviewed-on: https://go-review.googlesource.com/19820
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/unicode/utf16/utf16_test.go

@@ -147,3 +147,56 @@ func TestIsSurrogate(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkDecodeValidASCII(b *testing.B) {
+	// "hello world"
+	data := []uint16{104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100}
+	for i := 0; i < b.N; i++ {
+		Decode(data)
+	}
+}
+
+func BenchmarkDecodeValidJapaneseChars(b *testing.B) {
+	// "日本語日本語日本語"
+	data := []uint16{26085, 26412, 35486, 26085, 26412, 35486, 26085, 26412, 35486}
+	for i := 0; i < b.N; i++ {
+		Decode(data)
+	}
+}
+
+func BenchmarkDecodeRune(b *testing.B) {
+	rs := make([]rune, 10)
+	// U+1D4D0 to U+1D4D4: MATHEMATICAL BOLD SCRIPT CAPITAL LETTERS
+	for i, u := range []rune{'𝓐', '𝓑', '𝓒', '𝓓', '𝓔'} {
+		rs[2*i], rs[2*i+1] = EncodeRune(u)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for j := 0; j < 5; j++ {
+			DecodeRune(rs[2*j], rs[2*j+1])
+		}
+	}
+}
+
+func BenchmarkEncodeValidASCII(b *testing.B) {
+	data := []rune{'h', 'e', 'l', 'l', 'o'}
+	for i := 0; i < b.N; i++ {
+		Encode(data)
+	}
+}
+
+func BenchmarkEncodeValidJapaneseChars(b *testing.B) {
+	data := []rune{'日', '本', '語'}
+	for i := 0; i < b.N; i++ {
+		Encode(data)
+	}
+}
+
+func BenchmarkEncodeRune(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, u := range []rune{'𝓐', '𝓑', '𝓒', '𝓓', '𝓔'} {
+			EncodeRune(u)
+		}
+	}
+}