code review 14488043: encoding/binary: faster littleEndian on i386/amd64 and ...

encoding/binary: faster littleEndian on i386/amd64 and varint

Make use of unsafe.Pointer casting on i386/amd for little endian
read/write.
(change of BigEndian speed is benchmark noise)
Unroll a bit PutUvarint.

benchmark                          old ns/op    new ns/op    delta
BenchmarkReadSlice1000Int32sBE         10640        10679   +0.37%
BenchmarkReadSlice1000Int32sLE         10515         9096  -13.50%
BenchmarkReadStructBE                   2068         2163   +4.59%
BenchmarkReadStructLE                   2073         2070   -0.14%
BenchmarkReadIntsBE                      808          797   -1.36%
BenchmarkReadIntsLE                      807          780   -3.35%
BenchmarkWriteIntsBE                    1445         1474   +2.01%
BenchmarkWriteIntsLE                    1448         1422   -1.80%
BenchmarkWriteSlice1000Int32sBE        10661        10660   -0.01%
BenchmarkWriteSlice1000Int32sLE        10549         9242  -12.39%
BenchmarkPutUvarint32                     31           29   -6.62%
BenchmarkPutUvarint64                     89           86   -3.36%

benchmark                           old MB/s     new MB/s  speedup
BenchmarkReadSlice1000Int32sBE        375.92       374.54    1.00x
BenchmarkReadSlice1000Int32sLE        380.40       439.73    1.16x
BenchmarkReadStructBE                  33.83        32.35    0.96x
BenchmarkReadStructLE                  33.77        33.82    1.00x
BenchmarkReadIntsBE                    37.13        37.63    1.01x
BenchmarkReadIntsLE                    37.14        38.43    1.03x
BenchmarkWriteIntsBE                   20.76        20.34    0.98x
BenchmarkWriteIntsLE                   20.71        21.09    1.02x
BenchmarkWriteSlice1000Int32sBE       375.16       375.23    1.00x
BenchmarkWriteSlice1000Int32sLE       379.16       432.80    1.14x
BenchmarkPutUvarint32                 126.30       135.05    1.07x
BenchmarkPutUvarint64                  89.51        92.65    1.04x

[funny.falcon, 2013-10-07 12:42:54]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

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

[0xjnml, 2013-10-07 12:53:15]

On 2013/10/07 12:42:54, funny.falcon wrote:
> Hello mailto:golang-dev@googlegroups.com (cc:
mailto:golang-dev@googlegroups.com),
> 
> I'd like you to review this change to
> https://code.google.com/p/go

The averaged gain is IMHO not worth of introducing package unsafe into
encoding/binary.

-j

[r, 2013-10-07 16:34:21]

encoding/binary will not use unsafe. Also, we're in a freeze so changes
like this must wait until after the release.

-rob