code review 12694048: encoding/binary: fast path for reading slices

encoding/binary: fast path for reading slices

Again, it still allocates but the code is simple.

benchmark                       old ns/op    new ns/op    delta
BenchmarkReadSlice1000Int32s        35580        11465  -67.78%

benchmark                        old MB/s     new MB/s  speedup
BenchmarkReadSlice1000Int32s       112.42       348.86    3.10x

[r, 2013-08-09 22:07:04]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/

[bradfitz, 2013-08-09 22:24:59]

LGTM

https://codereview.appspot.com/12694048/diff/1/src/pkg/encoding/binary/binary.go
File src/pkg/encoding/binary/binary.go (right):

https://codereview.appspot.com/12694048/diff/1/src/pkg/encoding/binary/binary...
src/pkg/encoding/binary/binary.go:141: if n > 8 {
n > len(b) ?

https://codereview.appspot.com/12694048/diff/1/src/pkg/encoding/binary/binary...
src/pkg/encoding/binary/binary.go:612: // intDestSize returns the size of the
integer pointer or slice type that data points to,
this function name and/or comment should change.

the comment update didn't help me understand what it did it all.  I had to read
the code.

Maybe:

// If data is a pointer to an integer or is a slice of integers, intDestSize
returns the size of
// the referenced memory in bytes, otherwise it returns 0.

[r, 2013-08-09 22:40:40]

*** Submitted as https://code.google.com/p/go/source/detail?r=04726e184720 ***

encoding/binary: fast path for reading slices

Again, it still allocates but the code is simple.

benchmark                       old ns/op    new ns/op    delta
BenchmarkReadSlice1000Int32s        35580        11465  -67.78%

benchmark                        old MB/s     new MB/s  speedup
BenchmarkReadSlice1000Int32s       112.42       348.86    3.10x

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/12694048

[bradfitz, 2013-08-09 22:50:04]

https://codereview.appspot.com/12694048/diff/6001/src/pkg/encoding/binary/bin...
File src/pkg/encoding/binary/binary.go (right):

https://codereview.appspot.com/12694048/diff/6001/src/pkg/encoding/binary/bin...
src/pkg/encoding/binary/binary.go:612: // intDestSize returns the size of the
data required to represent the data when encoded.
this says nothing about 0 meaning unsupported anymore.