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image/jpeg: small memory layout optimization for encoding.

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Before:
jpeg.BenchmarkEncodeRGBOpaque ... 23.29 MB/s
jpeg.BenchmarkEncodeRGBOpaque ... 23.27 MB/s
jpeg.BenchmarkEncodeRGBOpaque ... 23.17 MB/s

After:
jpeg.BenchmarkEncodeRGBOpaque ... 23.42 MB/s
jpeg.BenchmarkEncodeRGBOpaque ... 23.34 MB/s
jpeg.BenchmarkEncodeRGBOpaque ... 23.33 MB/s

R=rsc
CC=golang-dev
https://golang.org/cl/4538077
This commit is contained in:
Nigel Tao 2011-05-18 14:39:37 -07:00
parent e7db6d78a2
commit 0a2650f398
1 changed files with 6 additions and 7 deletions
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13
src/pkg/image/jpeg/writer.go
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@ -221,8 +221,7 @@ type encoder struct {
// buf is a scratch buffer.
buf [16]byte
// bits and nBits are accumulated bits to write to w.
bits uint32
nBits uint8
bits, nBits uint32
// quant is the scaled quantization tables.
quant [nQuantIndex][blockSize]byte
}
@ -250,7 +249,7 @@ func (e *encoder) writeByte(b byte) {
// emit emits the least significant nBits bits of bits to the bitstream.
// The precondition is bits < 1<<nBits && nBits <= 16.
func (e *encoder) emit(bits uint32, nBits uint8) {
func (e *encoder) emit(bits, nBits uint32) {
nBits += e.nBits
bits <<= 32 - nBits
bits |= e.bits
@ -269,7 +268,7 @@ func (e *encoder) emit(bits uint32, nBits uint8) {
// emitHuff emits the given value with the given Huffman encoder.
func (e *encoder) emitHuff(h huffIndex, value int) {
x := theHuffmanLUT[h][value]
e.emit(x&(1<<24-1), uint8(x>>24))
e.emit(x&(1<<24-1), x>>24)
}
// emitHuffRLE emits a run of runLength copies of value encoded with the given
@ -279,11 +278,11 @@ func (e *encoder) emitHuffRLE(h huffIndex, runLength, value int) {
if a < 0 {
a, b = -value, value-1
}
var nBits uint8
var nBits uint32
if a < 0x100 {
nBits = bitCount[a]
nBits = uint32(bitCount[a])
} else {
nBits = 8 + bitCount[a>>8]
nBits = 8 + uint32(bitCount[a>>8])
}
e.emitHuff(h, runLength<<4|int(nBits))
if nBits > 0 {