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flate: Faster token writer, 1-2% on fastest #489

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merged 5 commits into from Feb 5, 2022
Merged

flate: Faster token writer, 1-2% on fastest #489

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8c3aa71
flate: Faster token writer
klauspost Feb 4, 2022
89706a7
Remove combined offsets
klauspost Feb 4, 2022
ce81e01
Revert "Remove combined offsets"
klauspost Feb 4, 2022
377f4bf
Move masking.
klauspost Feb 4, 2022
5653fe7
Update docs
klauspost Feb 4, 2022
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42 changes: 24 additions & 18 deletions flate/huffman_bit_writer.go
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Expand Up @@ -36,8 +36,11 @@ const (
bufferSize = bufferFlushSize + 8
)

// Minimum length code that emits bits.
const lengthExtraBitsMinCode = 8

// The number of extra bits needed by length code X - LENGTH_CODES_START.
var lengthExtraBits = [32]int8{
var lengthExtraBits = [32]uint8{
/* 257 */ 0, 0, 0,
/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
Expand All @@ -51,6 +54,9 @@ var lengthBase = [32]uint8{
64, 80, 96, 112, 128, 160, 192, 224, 255,
}

// Minimum offset code that emits bits.
const offsetExtraBitsMinCode = 4

// offset code word extra bits.
var offsetExtraBits = [32]int8{
0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
Expand Down Expand Up @@ -78,10 +84,10 @@ func init() {

for i := range offsetCombined[:] {
// Don't use extended window values...
if offsetBase[i] > 0x006000 {
if offsetExtraBits[i] == 0 || offsetBase[i] > 0x006000 {
continue
}
offsetCombined[i] = uint32(offsetExtraBits[i])<<16 | (offsetBase[i])
offsetCombined[i] = uint32(offsetExtraBits[i]) | (offsetBase[i] << 8)
}
}

Expand All @@ -97,7 +103,7 @@ type huffmanBitWriter struct {
// Data waiting to be written is bytes[0:nbytes]
// and then the low nbits of bits.
bits uint64
nbits uint16
nbits uint8
nbytes uint8
lastHuffMan bool
literalEncoding *huffmanEncoder
Expand Down Expand Up @@ -215,7 +221,7 @@ func (w *huffmanBitWriter) write(b []byte) {
_, w.err = w.writer.Write(b)
}

func (w *huffmanBitWriter) writeBits(b int32, nb uint16) {
func (w *huffmanBitWriter) writeBits(b int32, nb uint8) {
w.bits |= uint64(b) << (w.nbits & 63)
w.nbits += nb
if w.nbits >= 48 {
Expand Down Expand Up @@ -858,12 +864,12 @@ func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode)

// Write the length
length := t.length()
lengthCode := lengthCode(length)
lengthCode := lengthCode(length) & 31
if false {
w.writeCode(lengths[lengthCode&31])
w.writeCode(lengths[lengthCode])
} else {
// inlined
c := lengths[lengthCode&31]
c := lengths[lengthCode]
bits |= uint64(c.code) << (nbits & 63)
nbits += c.len
if nbits >= 48 {
Expand All @@ -883,10 +889,10 @@ func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode)
}
}

extraLengthBits := uint16(lengthExtraBits[lengthCode&31])
if extraLengthBits > 0 {
if lengthCode >= lengthExtraBitsMinCode {
extraLengthBits := lengthExtraBits[lengthCode]
//w.writeBits(extraLength, extraLengthBits)
extraLength := int32(length - lengthBase[lengthCode&31])
extraLength := int32(length - lengthBase[lengthCode])
bits |= uint64(extraLength) << (nbits & 63)
nbits += extraLengthBits
if nbits >= 48 {
Expand All @@ -907,10 +913,9 @@ func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode)
}
// Write the offset
offset := t.offset()
offsetCode := offset >> 16
offset &= matchOffsetOnlyMask
offsetCode := (offset >> 16) & 31
if false {
w.writeCode(offs[offsetCode&31])
w.writeCode(offs[offsetCode])
} else {
// inlined
c := offs[offsetCode]
Expand All @@ -932,11 +937,12 @@ func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode)
}
}
}
offsetComb := offsetCombined[offsetCode]
if offsetComb > 1<<16 {

if offsetCode >= offsetExtraBitsMinCode {
offsetComb := offsetCombined[offsetCode]
//w.writeBits(extraOffset, extraOffsetBits)
bits |= uint64(offset-(offsetComb&0xffff)) << (nbits & 63)
nbits += uint16(offsetComb >> 16)
bits |= uint64((offset-(offsetComb>>8))&matchOffsetOnlyMask) << (nbits & 63)
nbits += uint8(offsetComb)
if nbits >= 48 {
binary.LittleEndian.PutUint64(w.bytes[nbytes:], bits)
//*(*uint64)(unsafe.Pointer(&w.bytes[nbytes])) = bits
Expand Down
11 changes: 6 additions & 5 deletions flate/huffman_code.go
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Expand Up @@ -17,7 +17,8 @@ const (

// hcode is a huffman code with a bit code and bit length.
type hcode struct {
code, len uint16
code uint16
len uint8
}

type huffmanEncoder struct {
Expand Down Expand Up @@ -56,7 +57,7 @@ type levelInfo struct {
}

// set sets the code and length of an hcode.
func (h *hcode) set(code uint16, length uint16) {
func (h *hcode) set(code uint16, length uint8) {
h.len = length
h.code = code
}
Expand All @@ -80,7 +81,7 @@ func generateFixedLiteralEncoding() *huffmanEncoder {
var ch uint16
for ch = 0; ch < literalCount; ch++ {
var bits uint16
var size uint16
var size uint8
switch {
case ch < 144:
// size 8, 000110000 .. 10111111
Expand All @@ -99,7 +100,7 @@ func generateFixedLiteralEncoding() *huffmanEncoder {
bits = ch + 192 - 280
size = 8
}
codes[ch] = hcode{code: reverseBits(bits, byte(size)), len: size}
codes[ch] = hcode{code: reverseBits(bits, size), len: size}
}
return h
}
Expand Down Expand Up @@ -296,7 +297,7 @@ func (h *huffmanEncoder) assignEncodingAndSize(bitCount []int32, list []literalN

sortByLiteral(chunk)
for _, node := range chunk {
h.codes[node.literal] = hcode{code: reverseBits(code, uint8(n)), len: uint16(n)}
h.codes[node.literal] = hcode{code: reverseBits(code, uint8(n)), len: uint8(n)}
code++
}
list = list[0 : len(list)-int(bits)]
Expand Down
13 changes: 6 additions & 7 deletions flate/token.go
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Expand Up @@ -13,11 +13,10 @@ import (
)

const (
// From top
// 2 bits: type 0 = literal 1=EOF 2=Match 3=Unused
// 8 bits: xlength = length - MIN_MATCH_LENGTH
// 5 bits offsetcode
// 16 bits xoffset = offset - MIN_OFFSET_SIZE, or literal
// bits 0-16 xoffset = offset - MIN_OFFSET_SIZE, or literal - 16 bits
// bits 16-22 offsetcode - 5 bits
// bits 22-30 xlength = length - MIN_MATCH_LENGTH - 8 bits
// bits 30-32 type 0 = literal 1=EOF 2=Match 3=Unused - 2 bits
lengthShift = 22
offsetMask = 1<<lengthShift - 1
typeMask = 3 << 30
Expand Down Expand Up @@ -356,8 +355,8 @@ func (t token) offset() uint32 { return uint32(t) & offsetMask }

func (t token) length() uint8 { return uint8(t >> lengthShift) }

// The code is never more than 8 bits, but is returned as uint32 for convenience.
func lengthCode(len uint8) uint32 { return uint32(lengthCodes[len]) }
// Convert length to code.
func lengthCode(len uint8) uint8 { return lengthCodes[len] }

// Returns the offset code corresponding to a specific offset
func offsetCode(off uint32) uint32 {
Expand Down