compress/flate: add pure huffman deflater
Add a "HuffmanOnly" compression level, where the input is
only entropy encoded.
The output is fully inflate compatible. Typical compression
is reduction is about 50% of typical level 1 compression, however
the compression time is very stable, and does not vary as much as
nearly as much level 1 compression (or Snappy).
This mode is useful for:
* HTTP compression in a CPU limited environment.
* Entropy encoding Snappy compressed data, for archiving, etc.
* Compression where compression time needs to be predictable.
* Fast network transfer.
Snappy "usually" performs inbetween this and level 1 compression-wise,
but at the same speed as "Huffman", so this is not a replacement,
but a good supplement for Snappy, since it usually can compress
Snappy output further.
This is implemented as level -2, since this would be too much of a
compression reduction to replace level 1.
>go test -bench=Encode -cpu=1
BenchmarkEncodeDigitsHuffman1e4 30000 52334 ns/op 191.08 MB/s
BenchmarkEncodeDigitsHuffman1e5 3000 518343 ns/op 192.92 MB/s
BenchmarkEncodeDigitsHuffman1e6 300
5356884 ns/op 186.68 MB/s
BenchmarkEncodeDigitsSpeed1e4 5000 324214 ns/op 30.84 MB/s
BenchmarkEncodeDigitsSpeed1e5 500
3952614 ns/op 25.30 MB/s
BenchmarkEncodeDigitsSpeed1e6 30
40760350 ns/op 24.53 MB/s
BenchmarkEncodeDigitsDefault1e4 5000 387056 ns/op 25.84 MB/s
BenchmarkEncodeDigitsDefault1e5 300
5950614 ns/op 16.80 MB/s
BenchmarkEncodeDigitsDefault1e6 20
63842195 ns/op 15.66 MB/s
BenchmarkEncodeDigitsCompress1e4 5000 391859 ns/op 25.52 MB/s
BenchmarkEncodeDigitsCompress1e5 300
5707112 ns/op 17.52 MB/s
BenchmarkEncodeDigitsCompress1e6 20
59839465 ns/op 16.71 MB/s
BenchmarkEncodeTwainHuffman1e4 20000 73498 ns/op 136.06 MB/s
BenchmarkEncodeTwainHuffman1e5 2000 595892 ns/op 167.82 MB/s
BenchmarkEncodeTwainHuffman1e6 200
6059016 ns/op 165.04 MB/s
BenchmarkEncodeTwainSpeed1e4 5000 321212 ns/op 31.13 MB/s
BenchmarkEncodeTwainSpeed1e5 500
2823873 ns/op 35.41 MB/s
BenchmarkEncodeTwainSpeed1e6 50
27237864 ns/op 36.71 MB/s
BenchmarkEncodeTwainDefault1e4 3000 454634 ns/op 22.00 MB/s
BenchmarkEncodeTwainDefault1e5 200
6859537 ns/op 14.58 MB/s
BenchmarkEncodeTwainDefault1e6 20
71547405 ns/op 13.98 MB/s
BenchmarkEncodeTwainCompress1e4 3000 462307 ns/op 21.63 MB/s
BenchmarkEncodeTwainCompress1e5 200
7534992 ns/op 13.27 MB/s
BenchmarkEncodeTwainCompress1e6 20
80353365 ns/op 12.45 MB/s
PASS
ok compress/flate 55.333s
Change-Id: I8e12ad13220e50d4cf7ddba6f292333efad61b0c
Reviewed-on: https://go-review.googlesource.com/20982
Reviewed-by: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Nigel Tao <nigeltao@golang.org>