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compress/flate: optimize history-copy decoding.
The forwardCopy function could be re-written in asm, and the copyHuff method could probably be rolled into huffmanBlock and copyHist, but I'm leaving those changes for future CLs. compress/flate benchmarks: benchmark old ns/op new ns/op delta BenchmarkDecoderBestSpeed1K 385327 435140 +12.93% BenchmarkDecoderBestSpeed10K 1245190 1062112 -14.70% BenchmarkDecoderBestSpeed100K 8512365 5833680 -31.47% BenchmarkDecoderDefaultCompression1K 382225 421301 +10.22% BenchmarkDecoderDefaultCompression10K 867950 613890 -29.27% BenchmarkDecoderDefaultCompression100K 5658240 2466726 -56.40% BenchmarkDecoderBestCompression1K 383760 421634 +9.87% BenchmarkDecoderBestCompression10K 867743 614671 -29.16% BenchmarkDecoderBestCompression100K 5660160 2464996 -56.45% image/png benchmarks: benchmark old ns/op new ns/op delta BenchmarkDecodeGray 2540834 2389624 -5.95% BenchmarkDecodeNRGBAGradient 10052700 9534565 -5.15% BenchmarkDecodeNRGBAOpaque 8704710 8163430 -6.22% BenchmarkDecodePaletted 1458779 1325017 -9.17% BenchmarkDecodeRGB 7183606 6794668 -5.41% Wall time for Denis Cheremisov's PNG-decoding program given in https://groups.google.com/group/golang-nuts/browse_thread/thread/22aa8a05040fdd49 Before: 3.07s After: 2.32s Delta: -24% Before profile: Total: 304 samples 159 52.3% 52.3% 251 82.6% compress/flate.(*decompressor).huffmanBlock 58 19.1% 71.4% 76 25.0% compress/flate.(*decompressor).huffSym 32 10.5% 81.9% 32 10.5% hash/adler32.update 16 5.3% 87.2% 22 7.2% bufio.(*Reader).ReadByte 16 5.3% 92.4% 37 12.2% compress/flate.(*decompressor).moreBits 7 2.3% 94.7% 7 2.3% hash/crc32.update 7 2.3% 97.0% 7 2.3% runtime.memmove 5 1.6% 98.7% 5 1.6% scanblock 2 0.7% 99.3% 9 3.0% runtime.copy 1 0.3% 99.7% 1 0.3% compress/flate.(*huffmanDecoder).init After profile: Total: 230 samples 59 25.7% 25.7% 70 30.4% compress/flate.(*decompressor).huffSym 45 19.6% 45.2% 45 19.6% hash/adler32.update 35 15.2% 60.4% 35 15.2% compress/flate.forwardCopy 20 8.7% 69.1% 151 65.7% compress/flate.(*decompressor).huffmanBlock 16 7.0% 76.1% 24 10.4% compress/flate.(*decompressor).moreBits 15 6.5% 82.6% 15 6.5% runtime.memmove 11 4.8% 87.4% 50 21.7% compress/flate.(*decompressor).copyHist 7 3.0% 90.4% 7 3.0% hash/crc32.update 6 2.6% 93.0% 9 3.9% bufio.(*Reader).ReadByte 4 1.7% 94.8% 4 1.7% runtime.slicearray R=rsc, rogpeppe, dave CC=golang-dev, krasin https://golang.org/cl/6127064
This commit is contained in:
Nigel Tao
parent
84ce0f7687
commit
4de15a5cda
17
src/pkg/compress/flate/copy.go
Normal file
17
src/pkg/compress/flate/copy.go
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@ -0,0 +1,17 @@
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// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package flate
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// forwardCopy is like the built-in copy function except that it always goes
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// forward from the start, even if the dst and src overlap.
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func forwardCopy(dst, src []byte) int {
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if len(src) > len(dst) {
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src = src[:len(dst)]
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}
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for i, x := range src {
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dst[i] = x
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}
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return len(src)
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}
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42
src/pkg/compress/flate/copy_test.go
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42
src/pkg/compress/flate/copy_test.go
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@ -0,0 +1,42 @@
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// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package flate
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import (
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"testing"
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)
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func TestForwardCopy(t *testing.T) {
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testCases := []struct {
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dst0, dst1 int
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src0, src1 int
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want string
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}{
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{0, 9, 0, 9, "012345678"},
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{0, 5, 4, 9, "45678"},
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{4, 9, 0, 5, "01230"},
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{1, 6, 3, 8, "34567"},
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{3, 8, 1, 6, "12121"},
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{0, 9, 3, 6, "345"},
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{3, 6, 0, 9, "012"},
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{1, 6, 0, 9, "00000"},
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{0, 4, 7, 8, "7"},
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{0, 1, 6, 8, "6"},
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{4, 4, 6, 9, ""},
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{2, 8, 6, 6, ""},
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{0, 0, 0, 0, ""},
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}
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for _, tc := range testCases {
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b := []byte("012345678")
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dst := b[tc.dst0:tc.dst1]
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src := b[tc.src0:tc.src1]
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n := forwardCopy(dst, src)
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got := string(dst[:n])
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if got != tc.want {
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t.Errorf("dst=b[%d:%d], src=b[%d:%d]: got %q, want %q",
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tc.dst0, tc.dst1, tc.src0, tc.src1, got, tc.want)
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}
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}
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}
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@ -505,51 +505,49 @@ func (f *decompressor) huffmanBlock() {
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return
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}
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p := f.hp - dist
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if p < 0 {
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p += len(f.hist)
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}
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for i := 0; i < length; i++ {
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f.hist[f.hp] = f.hist[p]
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f.hp++
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p++
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if f.hp == len(f.hist) {
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// After flush continue copying out of history.
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f.copyLen = length - (i + 1)
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f.copyDist = dist
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f.flush((*decompressor).copyHuff)
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return
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}
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if p == len(f.hist) {
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p = 0
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}
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f.copyLen, f.copyDist = length, dist
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if f.copyHist() {
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return
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}
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}
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panic("unreached")
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}
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func (f *decompressor) copyHuff() {
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length := f.copyLen
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dist := f.copyDist
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p := f.hp - dist
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// copyHist copies f.copyLen bytes from f.hist (f.copyDist bytes ago) to itself.
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// It reports whether the f.hist buffer is full.
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func (f *decompressor) copyHist() bool {
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p := f.hp - f.copyDist
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if p < 0 {
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p += len(f.hist)
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}
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for i := 0; i < length; i++ {
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f.hist[f.hp] = f.hist[p]
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f.hp++
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p++
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for f.copyLen > 0 {
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n := f.copyLen
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if x := len(f.hist) - f.hp; n > x {
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n = x
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}
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if x := len(f.hist) - p; n > x {
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n = x
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}
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forwardCopy(f.hist[f.hp:f.hp+n], f.hist[p:p+n])
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p += n
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f.hp += n
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f.copyLen -= n
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if f.hp == len(f.hist) {
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f.copyLen = length - (i + 1)
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// After flush continue copying out of history.
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f.flush((*decompressor).copyHuff)
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return
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return true
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}
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if p == len(f.hist) {
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p = 0
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}
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}
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return false
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}
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// Continue processing Huffman block.
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func (f *decompressor) copyHuff() {
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if f.copyHist() {
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return
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}
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f.huffmanBlock()
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}
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@ -584,9 +582,9 @@ func (f *decompressor) dataBlock() {
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f.copyData()
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}
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// copyData copies f.copyLen bytes from the underlying reader into f.hist.
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// It pauses for reads when f.hist is full.
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func (f *decompressor) copyData() {
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// Read f.dataLen bytes into history,
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// pausing for reads as history fills.
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n := f.copyLen
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for n > 0 {
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m := len(f.hist) - f.hp
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