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compress/flate: reduce memory pressure at cost of additional arithmetic operation.

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R=rsc
CC=golang-dev
https://golang.org/cl/5555070
This commit is contained in:
Ivan Krasin 2012-01-23 09:19:39 -05:00 committed by Russ Cox
parent 427b5bddcd
commit d7e34051fc
1 changed files with 11 additions and 23 deletions
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28
src/pkg/compress/flate/deflate.go
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@ -73,6 +73,7 @@ type compressor struct {
chainHead int
hashHead []int
hashPrev []int
hashOffset int
// input window: unprocessed data is window[index:windowEnd]
index int
@ -104,20 +105,7 @@ func (d *compressor) fillDeflate(b []byte) int {
} else {
d.blockStart = skipNever
}
for i, h := range d.hashHead {
v := h - windowSize
if v < -1 {
v = -1
}
d.hashHead[i] = v
}
for i, h := range d.hashPrev {
v := h - windowSize
if v < -1 {
v = -1
}
d.hashPrev[i] = v
}
d.hashOffset += windowSize
}
n := copy(d.window[d.windowEnd:], b)
d.windowEnd += n
@ -188,7 +176,7 @@ func (d *compressor) findMatch(pos int, prevHead int, prevLength int, lookahead
// hashPrev[i & windowMask] has already been overwritten, so stop now.
break
}
if i = d.hashPrev[i&windowMask]; i < minIndex || i < 0 {
if i = d.hashPrev[i&windowMask] - d.hashOffset; i < minIndex || i < 0 {
break
}
}
@ -207,7 +195,7 @@ func (d *compressor) initDeflate() {
d.hashHead = make([]int, hashSize)
d.hashPrev = make([]int, windowSize)
d.window = make([]byte, 2*windowSize)
fillInts(d.hashHead, -1)
d.hashOffset = 1
d.tokens = make([]token, maxFlateBlockTokens, maxFlateBlockTokens+1)
d.length = minMatchLength - 1
d.offset = 0
@ -263,7 +251,7 @@ Loop:
d.hash = (d.hash<<hashShift + int(d.window[d.index+2])) & hashMask
d.chainHead = d.hashHead[d.hash]
d.hashPrev[d.index&windowMask] = d.chainHead
d.hashHead[d.hash] = d.index
d.hashHead[d.hash] = d.index + d.hashOffset
}
prevLength := d.length
prevOffset := d.offset
@ -274,10 +262,10 @@ Loop:
minIndex = 0
}
if d.chainHead >= minIndex &&
if d.chainHead-d.hashOffset >= minIndex &&
(d.fastSkipHashing != skipNever && lookahead > minMatchLength-1 ||
d.fastSkipHashing == skipNever && lookahead > prevLength && prevLength < d.lazy) {
if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead, minMatchLength-1, lookahead); ok {
if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
d.length = newLength
d.offset = newOffset
}
@ -310,7 +298,7 @@ Loop:
// Our chain should point to the previous value.
d.hashPrev[d.index&windowMask] = d.hashHead[d.hash]
// Set the head of the hash chain to us.
d.hashHead[d.hash] = d.index
d.hashHead[d.hash] = d.index + d.hashOffset
}
}
if d.fastSkipHashing == skipNever {