encoding/binary: fix error message

In the process, simplified internal sizeOf and
dataSize functions. Minor positive impact on
performance. Added test case.

benchmark                         old ns/op     new ns/op     delta
BenchmarkReadSlice1000Int32s      14006         14122         +0.83%
BenchmarkReadStruct               2508          2447          -2.43%
BenchmarkReadInts                 921           928           +0.76%
BenchmarkWriteInts                2086          2081          -0.24%
BenchmarkWriteSlice1000Int32s     13440         13497         +0.42%
BenchmarkPutUvarint32             28.5          26.3          -7.72%
BenchmarkPutUvarint64             81.3          76.7          -5.66%

benchmark                         old MB/s     new MB/s     speedup
BenchmarkReadSlice1000Int32s      285.58       283.24       0.99x
BenchmarkReadStruct               27.90        28.60        1.03x
BenchmarkReadInts                 32.57        32.31        0.99x
BenchmarkWriteInts                14.38        14.41        1.00x
BenchmarkWriteSlice1000Int32s     297.60       296.36       1.00x
BenchmarkPutUvarint32             140.55       151.92       1.08x
BenchmarkPutUvarint64             98.36        104.33       1.06x

Fixes #6818.

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/149290045

1 files changed, 21 insertions, 2 deletions

diff --git a/src/encoding/binary/binary_test.go b/src/encoding/binary/binary_test.go
index c80c90383a..8ee595fa47 100644
--- a/src/encoding/binary/binary_test.go
+++ b/src/encoding/binary/binary_test.go
@@ -289,6 +289,26 @@ func TestUnexportedRead(t *testing.T) {
 	Read(&buf, LittleEndian, &u2)
 }
 
+func TestReadErrorMsg(t *testing.T) {
+	var buf bytes.Buffer
+	read := func(data interface{}) {
+		err := Read(&buf, LittleEndian, data)
+		want := "binary.Read: invalid type " + reflect.TypeOf(data).String()
+		if err == nil {
+			t.Errorf("%T: got no error; want %q", data, want)
+			return
+		}
+		if got := err.Error(); got != want {
+			t.Errorf("%T: got %q; want %q", data, got, want)
+		}
+	}
+	read(0)
+	s := new(struct{})
+	read(&s)
+	p := &s
+	read(&p)
+}
+
 type byteSliceReader struct {
 	remain []byte
 }
@@ -315,8 +335,7 @@ func BenchmarkReadStruct(b *testing.B) {
 	bsr := &byteSliceReader{}
 	var buf bytes.Buffer
 	Write(&buf, BigEndian, &s)
-	n, _ := dataSize(reflect.ValueOf(s))
-	b.SetBytes(int64(n))
+	b.SetBytes(int64(dataSize(reflect.ValueOf(s))))
 	t := s
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {