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zstd: Faster CRC checking/skipping #696

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merged 2 commits into from Nov 25, 2022
+25 −19
Merged

zstd: Faster CRC checking/skipping #696

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eb034a2
zstd: Check ignoreChecksum option once
greatroar Nov 23, 2022
2f19fd3
zstd: Inline blockDec.checkCRC
greatroar Nov 23, 2022
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5 changes: 3 additions & 2 deletions zstd/blockdec.go
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Expand Up @@ -82,8 +82,9 @@ type blockDec struct {

err error

// Check against this crc
checkCRC []byte
// Check against this crc, if hasCRC is true.
checkCRC uint32
hasCRC bool

// Frame to use for singlethreaded decoding.
// Should not be used by the decoder itself since parent may be another frame.
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39 changes: 22 additions & 17 deletions zstd/decoder.go
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Expand Up @@ -5,7 +5,6 @@
package zstd

import (
"bytes"
"context"
"encoding/binary"
"io"
Expand Down Expand Up @@ -459,26 +458,28 @@ func (d *Decoder) nextBlock(blocking bool) (ok bool) {
println("got", len(d.current.b), "bytes, error:", d.current.err, "data crc:", tmp)
}

if !d.o.ignoreChecksum && len(next.b) > 0 {
if d.o.ignoreChecksum {
return true
}

if len(next.b) > 0 {
n, err := d.current.crc.Write(next.b)
if err == nil {
if n != len(next.b) {
d.current.err = io.ErrShortWrite
}
}
}
if next.err == nil && next.d != nil && len(next.d.checkCRC) != 0 {
got := d.current.crc.Sum64()
var tmp [4]byte
binary.LittleEndian.PutUint32(tmp[:], uint32(got))
if !d.o.ignoreChecksum && !bytes.Equal(tmp[:], next.d.checkCRC) {
if next.err == nil && next.d != nil && next.d.hasCRC {
got := uint32(d.current.crc.Sum64())
if got != next.d.checkCRC {
if debugDecoder {
println("CRC Check Failed:", tmp[:], " (got) !=", next.d.checkCRC, "(on stream)")
printf("CRC Check Failed: %08x (got) != %08x (on stream)\n", got, next.d.checkCRC)
}
d.current.err = ErrCRCMismatch
} else {
if debugDecoder {
println("CRC ok", tmp[:])
printf("CRC ok %08x\n", got)
}
}
}
Expand Down Expand Up @@ -918,18 +919,22 @@ decodeStream:
println("next block returned error:", err)
}
dec.err = err
dec.checkCRC = nil
dec.hasCRC = false
if dec.Last && frame.HasCheckSum && err == nil {
crc, err := frame.rawInput.readSmall(4)
if err != nil {
if len(crc) < 4 {
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if err == nil {
err = io.ErrUnexpectedEOF

}
println("CRC missing?", err)
dec.err = err
}
var tmp [4]byte
copy(tmp[:], crc)
dec.checkCRC = tmp[:]
if debugDecoder {
println("found crc to check:", dec.checkCRC)
} else {
dec.checkCRC = binary.LittleEndian.Uint32(crc)
dec.hasCRC = true
if debugDecoder {
printf("found crc to check: %08x\n", dec.checkCRC)
}
}
}
err = dec.err
Expand Down