Commit d7e34051 authored by Ivan Krasin's avatar Ivan Krasin Committed by Russ Cox

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

R=rsc
CC=golang-dev
https://golang.org/cl/5555070
parent 427b5bdd
......@@ -70,9 +70,10 @@ type compressor struct {
// If hashHead[hashValue] is within the current window, then
// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
// with the same hash value.
chainHead int
hashHead []int
hashPrev []int
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 {
......
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