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zstd: Replace bytes.Equal with smaller comparisons #695

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merged 1 commit into from
Nov 23, 2022
Merged

zstd: Replace bytes.Equal with smaller comparisons #695

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5 changes: 2 additions & 3 deletions zstd/decodeheader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@
package zstd

import (
"bytes"
"encoding/binary"
"errors"
"io"
Expand Down Expand Up @@ -102,8 +101,8 @@ func (h *Header) Decode(in []byte) error {
}
h.HeaderSize += 4
b, in := in[:4], in[4:]
if !bytes.Equal(b, frameMagic) {
if !bytes.Equal(b[1:4], skippableFrameMagic) || b[0]&0xf0 != 0x50 {
if string(b) != frameMagic {
if string(b[1:4]) != skippableFrameMagic || b[0]&0xf0 != 0x50 {
return ErrMagicMismatch
}
if len(in) < 4 {
Expand Down
5 changes: 2 additions & 3 deletions zstd/dict.go
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Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
package zstd

import (
"bytes"
"encoding/binary"
"errors"
"fmt"
Expand All @@ -20,7 +19,7 @@ type dict struct {
content []byte
}

var dictMagic = [4]byte{0x37, 0xa4, 0x30, 0xec}
const dictMagic = "\x37\xa4\x30\xec"

// ID returns the dictionary id or 0 if d is nil.
func (d *dict) ID() uint32 {
Expand Down Expand Up @@ -50,7 +49,7 @@ func loadDict(b []byte) (*dict, error) {
ofDec: sequenceDec{fse: &fseDecoder{}},
mlDec: sequenceDec{fse: &fseDecoder{}},
}
if !bytes.Equal(b[:4], dictMagic[:]) {
if string(b[:4]) != dictMagic {
return nil, ErrMagicMismatch
}
d.id = binary.LittleEndian.Uint32(b[4:8])
Expand Down
33 changes: 14 additions & 19 deletions zstd/framedec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
package zstd

import (
"bytes"
"encoding/binary"
"encoding/hex"
"errors"
"io"
Expand Down Expand Up @@ -43,9 +43,9 @@ const (
MaxWindowSize = 1 << 29
)

var (
frameMagic = []byte{0x28, 0xb5, 0x2f, 0xfd}
skippableFrameMagic = []byte{0x2a, 0x4d, 0x18}
const (
frameMagic = "\x28\xb5\x2f\xfd"
skippableFrameMagic = "\x2a\x4d\x18"
)

func newFrameDec(o decoderOptions) *frameDec {
Expand Down Expand Up @@ -89,9 +89,9 @@ func (d *frameDec) reset(br byteBuffer) error {
copy(signature[1:], b)
}

if !bytes.Equal(signature[1:4], skippableFrameMagic) || signature[0]&0xf0 != 0x50 {
if string(signature[1:4]) != skippableFrameMagic || signature[0]&0xf0 != 0x50 {
if debugDecoder {
println("Not skippable", hex.EncodeToString(signature[:]), hex.EncodeToString(skippableFrameMagic))
println("Not skippable", hex.EncodeToString(signature[:]), hex.EncodeToString([]byte(skippableFrameMagic)))
}
// Break if not skippable frame.
break
Expand All @@ -114,9 +114,9 @@ func (d *frameDec) reset(br byteBuffer) error {
return err
}
}
if !bytes.Equal(signature[:], frameMagic) {
if string(signature[:]) != frameMagic {
if debugDecoder {
println("Got magic numbers: ", signature, "want:", frameMagic)
println("Got magic numbers: ", signature, "want:", []byte(frameMagic))
}
return ErrMagicMismatch
}
Expand Down Expand Up @@ -305,7 +305,7 @@ func (d *frameDec) checkCRC() error {
}

// We can overwrite upper tmp now
want, err := d.rawInput.readSmall(4)
buf, err := d.rawInput.readSmall(4)
if err != nil {
println("CRC missing?", err)
return err
Expand All @@ -315,22 +315,17 @@ func (d *frameDec) checkCRC() error {
return nil
}

var tmp [4]byte
got := d.crc.Sum64()
// Flip to match file order.
tmp[0] = byte(got >> 0)
tmp[1] = byte(got >> 8)
tmp[2] = byte(got >> 16)
tmp[3] = byte(got >> 24)
want := binary.LittleEndian.Uint32(buf[:4])
got := uint32(d.crc.Sum64())

if !bytes.Equal(tmp[:], want) {
if got != want {
if debugDecoder {
println("CRC Check Failed:", tmp[:], "!=", want)
printf("CRC check failed: got %08x, want %08x\n", got, want)
}
return ErrCRCMismatch
}
if debugDecoder {
println("CRC ok", tmp[:])
printf("CRC ok %08x\n", got)
}
return nil
}
Expand Down