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[huff0] Add x86 specialisation of Decode4X #512

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merged 1 commit into from Mar 8, 2022
Merged

[huff0] Add x86 specialisation of Decode4X #512

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4 changes: 4 additions & 0 deletions huff0/autogen.go
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@@ -0,0 +1,4 @@
package huff0

//go:generate go run generate.go
//go:generate asmfmt -w decompress_amd64.s
5 changes: 5 additions & 0 deletions huff0/bitreader.go
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Expand Up @@ -165,6 +165,11 @@ func (b *bitReaderShifted) peekBitsFast(n uint8) uint16 {
return uint16(b.value >> ((64 - n) & 63))
}

// peekTopBits(n) is equvialent to peekBitFast(64 - n)
func (b *bitReaderShifted) peekTopBits(n uint8) uint16 {
return uint16(b.value >> n)
}

func (b *bitReaderShifted) advance(n uint8) {
b.bitsRead += n
b.value <<= n & 63
Expand Down
183 changes: 0 additions & 183 deletions huff0/decompress.go
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Expand Up @@ -725,189 +725,6 @@ func (d *Decoder) decompress1X8BitExactly(dst, src []byte) ([]byte, error) {
return dst, br.close()
}

// Decompress4X will decompress a 4X encoded stream.
// The length of the supplied input must match the end of a block exactly.
// The *capacity* of the dst slice must match the destination size of
// the uncompressed data exactly.
func (d *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
if len(d.dt.single) == 0 {
return nil, errors.New("no table loaded")
}
if len(src) < 6+(4*1) {
return nil, errors.New("input too small")
}
if use8BitTables && d.actualTableLog <= 8 {
return d.decompress4X8bit(dst, src)
}

var br [4]bitReaderShifted
// Decode "jump table"
start := 6
for i := 0; i < 3; i++ {
length := int(src[i*2]) | (int(src[i*2+1]) << 8)
if start+length >= len(src) {
return nil, errors.New("truncated input (or invalid offset)")
}
err := br[i].init(src[start : start+length])
if err != nil {
return nil, err
}
start += length
}
err := br[3].init(src[start:])
if err != nil {
return nil, err
}

// destination, offset to match first output
dstSize := cap(dst)
dst = dst[:dstSize]
out := dst
dstEvery := (dstSize + 3) / 4

const tlSize = 1 << tableLogMax
const tlMask = tlSize - 1
single := d.dt.single[:tlSize]

// Use temp table to avoid bound checks/append penalty.
buf := d.buffer()
var off uint8
var decoded int

// Decode 2 values from each decoder/loop.
const bufoff = 256
for {
if br[0].off < 4 || br[1].off < 4 || br[2].off < 4 || br[3].off < 4 {
break
}

{
const stream = 0
const stream2 = 1
br[stream].fillFast()
br[stream2].fillFast()

val := br[stream].peekBitsFast(d.actualTableLog)
val2 := br[stream2].peekBitsFast(d.actualTableLog)
v := single[val&tlMask]
v2 := single[val2&tlMask]
br[stream].advance(uint8(v.entry))
br[stream2].advance(uint8(v2.entry))
buf[stream][off] = uint8(v.entry >> 8)
buf[stream2][off] = uint8(v2.entry >> 8)

val = br[stream].peekBitsFast(d.actualTableLog)
val2 = br[stream2].peekBitsFast(d.actualTableLog)
v = single[val&tlMask]
v2 = single[val2&tlMask]
br[stream].advance(uint8(v.entry))
br[stream2].advance(uint8(v2.entry))
buf[stream][off+1] = uint8(v.entry >> 8)
buf[stream2][off+1] = uint8(v2.entry >> 8)
}

{
const stream = 2
const stream2 = 3
br[stream].fillFast()
br[stream2].fillFast()

val := br[stream].peekBitsFast(d.actualTableLog)
val2 := br[stream2].peekBitsFast(d.actualTableLog)
v := single[val&tlMask]
v2 := single[val2&tlMask]
br[stream].advance(uint8(v.entry))
br[stream2].advance(uint8(v2.entry))
buf[stream][off] = uint8(v.entry >> 8)
buf[stream2][off] = uint8(v2.entry >> 8)

val = br[stream].peekBitsFast(d.actualTableLog)
val2 = br[stream2].peekBitsFast(d.actualTableLog)
v = single[val&tlMask]
v2 = single[val2&tlMask]
br[stream].advance(uint8(v.entry))
br[stream2].advance(uint8(v2.entry))
buf[stream][off+1] = uint8(v.entry >> 8)
buf[stream2][off+1] = uint8(v2.entry >> 8)
}

off += 2

if off == 0 {
if bufoff > dstEvery {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 1")
}
copy(out, buf[0][:])
copy(out[dstEvery:], buf[1][:])
copy(out[dstEvery*2:], buf[2][:])
copy(out[dstEvery*3:], buf[3][:])
out = out[bufoff:]
decoded += bufoff * 4
// There must at least be 3 buffers left.
if len(out) < dstEvery*3 {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 2")
}
}
}
if off > 0 {
ioff := int(off)
if len(out) < dstEvery*3+ioff {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 3")
}
copy(out, buf[0][:off])
copy(out[dstEvery:], buf[1][:off])
copy(out[dstEvery*2:], buf[2][:off])
copy(out[dstEvery*3:], buf[3][:off])
decoded += int(off) * 4
out = out[off:]
}

// Decode remaining.
remainBytes := dstEvery - (decoded / 4)
for i := range br {
offset := dstEvery * i
endsAt := offset + remainBytes
if endsAt > len(out) {
endsAt = len(out)
}
br := &br[i]
bitsLeft := br.remaining()
for bitsLeft > 0 {
br.fill()
if offset >= endsAt {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 4")
}

// Read value and increment offset.
val := br.peekBitsFast(d.actualTableLog)
v := single[val&tlMask].entry
nBits := uint8(v)
br.advance(nBits)
bitsLeft -= uint(nBits)
out[offset] = uint8(v >> 8)
offset++
}
if offset != endsAt {
d.bufs.Put(buf)
return nil, fmt.Errorf("corruption detected: short output block %d, end %d != %d", i, offset, endsAt)
}
decoded += offset - dstEvery*i
err = br.close()
if err != nil {
return nil, err
}
}
d.bufs.Put(buf)
if dstSize != decoded {
return nil, errors.New("corruption detected: short output block")
}
return dst, nil
}

// Decompress4X will decompress a 4X encoded stream.
// The length of the supplied input must match the end of a block exactly.
// The *capacity* of the dst slice must match the destination size of
Expand Down
166 changes: 166 additions & 0 deletions huff0/decompress_amd64.go
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@@ -0,0 +1,166 @@
//go:build amd64 && !appengine && !noasm && gc
// +build amd64,!appengine,!noasm,gc

// This file contains the specialisation of Decoder.Decompress4X
// that uses an asm implementation of its main loop.
package huff0

import (
"errors"
"fmt"
)

// decompress4x_main_loop_x86 is an x86 assembler implementation
// of Decompress4X that uses BMI1 instructions.
// go:noescape
func decompress4x_main_loop_x86(pbr0, pbr1, pbr2, pbr3 *bitReaderShifted,
peekBits uint8, buf *byte, tbl *dEntrySingle) uint8

// Decompress4X will decompress a 4X encoded stream.
// The length of the supplied input must match the end of a block exactly.
// The *capacity* of the dst slice must match the destination size of
// the uncompressed data exactly.
func (d *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
if len(d.dt.single) == 0 {
return nil, errors.New("no table loaded")
}
if len(src) < 6+(4*1) {
return nil, errors.New("input too small")
}
if use8BitTables && d.actualTableLog <= 8 {
return d.decompress4X8bit(dst, src)
}

var br [4]bitReaderShifted
// Decode "jump table"
start := 6
for i := 0; i < 3; i++ {
length := int(src[i*2]) | (int(src[i*2+1]) << 8)
if start+length >= len(src) {
return nil, errors.New("truncated input (or invalid offset)")
}
err := br[i].init(src[start : start+length])
if err != nil {
return nil, err
}
start += length
}
err := br[3].init(src[start:])
if err != nil {
return nil, err
}

// destination, offset to match first output
dstSize := cap(dst)
dst = dst[:dstSize]
out := dst
dstEvery := (dstSize + 3) / 4

const tlSize = 1 << tableLogMax
const tlMask = tlSize - 1
single := d.dt.single[:tlSize]

// Use temp table to avoid bound checks/append penalty.
buf := d.buffer()
var off uint8
var decoded int

const debug = false

// see: bitReaderShifted.peekBitsFast()
peekBits := uint8((64 - d.actualTableLog) & 63)

// Decode 2 values from each decoder/loop.
const bufoff = 256
for {
if br[0].off < 4 || br[1].off < 4 || br[2].off < 4 || br[3].off < 4 {
break
}

off = decompress4x_main_loop_x86(&br[0], &br[1], &br[2], &br[3], peekBits, &buf[0][0], &single[0])
if debug {
fmt.Print("DEBUG: ")
fmt.Printf("off=%d,", off)
for i := 0; i < 4; i++ {
fmt.Printf(" br[%d]={bitsRead=%d, value=%x, off=%d}",
i, br[i].bitsRead, br[i].value, br[i].off)
}
fmt.Println("")
}

if off != 0 {
break
}

if bufoff > dstEvery {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 1")
}
copy(out, buf[0][:])
copy(out[dstEvery:], buf[1][:])
copy(out[dstEvery*2:], buf[2][:])
copy(out[dstEvery*3:], buf[3][:])
out = out[bufoff:]
decoded += bufoff * 4
// There must at least be 3 buffers left.
if len(out) < dstEvery*3 {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 2")
}
}
if off > 0 {
ioff := int(off)
if len(out) < dstEvery*3+ioff {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 3")
}
copy(out, buf[0][:off])
copy(out[dstEvery:], buf[1][:off])
copy(out[dstEvery*2:], buf[2][:off])
copy(out[dstEvery*3:], buf[3][:off])
decoded += int(off) * 4
out = out[off:]
}

// Decode remaining.
remainBytes := dstEvery - (decoded / 4)
for i := range br {
offset := dstEvery * i
endsAt := offset + remainBytes
if endsAt > len(out) {
endsAt = len(out)
}
br := &br[i]
bitsLeft := br.remaining()
for bitsLeft > 0 {
br.fill()
if offset >= endsAt {
d.bufs.Put(buf)
return nil, errors.New("corruption detected: stream overrun 4")
}

// Read value and increment offset.
val := br.peekBitsFast(d.actualTableLog)
v := single[val&tlMask].entry
nBits := uint8(v)
br.advance(nBits)
bitsLeft -= uint(nBits)
out[offset] = uint8(v >> 8)
offset++
}
if offset != endsAt {
d.bufs.Put(buf)
return nil, fmt.Errorf("corruption detected: short output block %d, end %d != %d", i, offset, endsAt)
}
decoded += offset - dstEvery*i
err = br.close()
if err != nil {
return nil, err
}
}
d.bufs.Put(buf)
if dstSize != decoded {
return nil, errors.New("corruption detected: short output block")
}
return dst, nil
}