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Since compiler is now able to generate conditional moves, we can replace
bit-tricks with simple if/else. This even results in slightly better performance:
name old time/op new time/op delta
DecodeDigits-6 13.4ms ± 4% 13.0ms ± 2% -2.63% (p=0.003 n=10+10)
DecodeTwain-6 37.5ms ± 1% 36.3ms ± 1% -3.03% (p=0.000 n=10+9)
DecodeRand-6 4.23ms ± 1% 4.07ms ± 1% -3.67% (p=0.000 n=10+9)
name old speed new speed delta
DecodeDigits-6 7.47MB/s ± 4% 7.67MB/s ± 2% +2.69% (p=0.002 n=10+10)
DecodeTwain-6 10.4MB/s ± 1% 10.7MB/s ± 1% +3.25% (p=0.000 n=10+8)
DecodeRand-6 3.87MB/s ± 1% 4.03MB/s ± 2% +4.08% (p=0.000 n=10+10)
diff --git a/src/compress/bzip2/huffman.go b/src/compress/bzip2/huffman.go
Change-Id: Ie96ef1a9e07013b07e78f22cdccd531f3341caca
Reviewed-on: https://go-review.googlesource.com/102015
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
Reviewed-by: Joe Tsai <joetsai@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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Change-Id: Ie4d23cdb81473a4c989a977a127479cf825084dc
Reviewed-on: https://go-review.googlesource.com/77850
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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The logic performs a series of shifts, which are useless given
that they are followed by an assignment that overrides the
value of the previous computation.
I suspect (but cannot prove) that this is leftover logic from an
original approach that attempted to store both the Huffman code
and the length within the same variable instead of using two
different variables as it currently does now.
Fixes #17949
Change-Id: Ibf6c807c6cef3b28bfdaf2b68d9bc13503ac21b2
Reviewed-on: https://go-review.googlesource.com/44091
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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Issue 6754 reports that Go bzip2 Decode function is much slower
(about 2.5x in go1.5) than the Python equivalent (which is
actually just a wrapper around the usual C library) on random data.
Profiling the code shows that half a dozen of CMP instructions in a
tight loop are responsibile for most of the execution time.
This patch reduces the number of branches of the loop, greatly
improving performance on random data and speeding up decoding of
real data.
name old time/op new time/op delta
DecodeDigits-4 9.28ms ± 1% 8.05ms ± 1% -13.18% (p=0.000 n=15+14)
DecodeTwain-4 28.9ms ± 2% 26.4ms ± 1% -8.57% (p=0.000 n=15+14)
DecodeRand-4 3.94ms ± 1% 3.06ms ± 1% -22.45% (p=0.000 n=15+14)
name old speed new speed delta
DecodeDigits-4 4.65MB/s ± 1% 5.36MB/s ± 1% +15.21% (p=0.000 n=13+14)
DecodeTwain-4 4.32MB/s ± 2% 4.72MB/s ± 1% +9.36% (p=0.000 n=15+14)
DecodeRand-4 4.27MB/s ± 1% 5.51MB/s ± 1% +28.86% (p=0.000 n=15+14)
I've run some benchmark comparing Go bzip2 implementation with the
usual Linux bzip2 command (which is written in C). On my machine
this patch brings go1.5
from ~2.26x to ~1.50x of bzip2 time (on 64MB random data)
from ~1.70x to ~1.50x of bzip2 time (on 100MB english text)
from ~2.00x to ~1.88x of bzip2 time (on 64MB /dev/zero data)
Fixes #6754
Change-Id: I3cb12d2c0c2243c1617edef1edc88f05f91d26d1
Reviewed-on: https://go-review.googlesource.com/13853
Reviewed-by: Nigel Tao <nigeltao@golang.org>
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Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.
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