tree 8b0e3d1aac786833efbac1bf4e6fcd6a241ec1b3
parent 51195a16b052437072a3e46972e348569f2a2f7a
author Nigel Tao <nigeltao@golang.org> 1455333098 +1100
committer Nigel Tao <nigeltao@golang.org> 1455333098 +1100

Change the encoder's hash table values from int to int32.

Doing s/int/int32/ in "var table [maxTableSize]int" saves 64 KiB of
stack space that needed zero'ing. maxTableSize is 1<<14, or 16384.

The benchmarks show the biggest effect for small src lengths, or for
mostly uncompressible data such as the JPEG file (possibly because the
multiple-byte skipping means that the src is effectively short).

On amd64:

benchmark                     old MB/s     new MB/s     speedup
BenchmarkWordsEncode1e1-8     3.05         5.71         1.87x
BenchmarkWordsEncode1e2-8     26.98        44.87        1.66x
BenchmarkWordsEncode1e3-8     130.87       156.72       1.20x
BenchmarkWordsEncode1e4-8     162.48       180.89       1.11x
BenchmarkWordsEncode1e5-8     132.35       131.27       0.99x
BenchmarkWordsEncode1e6-8     159.97       158.49       0.99x
BenchmarkRandomEncode-8       12340.86     13485.69     1.09x
Benchmark_ZFlat0-8            329.92       329.17       1.00x
Benchmark_ZFlat1-8            165.06       164.46       1.00x
Benchmark_ZFlat2-8            8955.25      10530.49     1.18x
Benchmark_ZFlat3-8            47.79        80.06        1.68x
Benchmark_ZFlat4-8            2650.55      2732.00      1.03x
Benchmark_ZFlat5-8            336.52       334.94       1.00x
Benchmark_ZFlat6-8            147.99       145.85       0.99x
Benchmark_ZFlat7-8            136.32       137.20       1.01x
Benchmark_ZFlat8-8            153.03       152.15       0.99x
Benchmark_ZFlat9-8            133.18       131.74       0.99x
Benchmark_ZFlat10-8           376.02       378.28       1.01x
Benchmark_ZFlat11-8           224.16       216.81       0.97x

Thanks to Klaus Post for the original suggestion on
https://github.com/golang/snappy/pull/23 but I hesitate to accept that
pull request in its entirety as it makes many changes, some more
complicated than this separable, self-contained s/int/int32/ change.