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zstd: Improve throughput of SpeedBestCompression encoder #699

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merged 1 commit into from Nov 26, 2022
Merged

zstd: Improve throughput of SpeedBestCompression encoder #699

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32 changes: 17 additions & 15 deletions zstd/enc_best.go
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Expand Up @@ -38,27 +38,29 @@ type match struct {
const highScore = 25000

// estBits will estimate output bits from predefined tables.
func (m *match) estBits(bitsPerByte int32) {
mlc := mlCode(uint32(m.length - zstdMinMatch))
var ofc uint8
if m.rep < 0 {
ofc = ofCode(uint32(m.s-m.offset) + 3)
} else {
ofc = ofCode(uint32(m.rep))
}
func (m *match) estBits(bitsPerByte int32, ofc, mlc uint8) {
// Cost, excluding
ofTT, mlTT := fsePredefEnc[tableOffsets].ct.symbolTT[ofc], fsePredefEnc[tableMatchLengths].ct.symbolTT[mlc]

// Add cost of match encoding...
m.est = int32(ofTT.outBits + mlTT.outBits)
m.est += int32(ofTT.deltaNbBits>>16 + mlTT.deltaNbBits>>16)
est := int32(ofTT.outBits + mlTT.outBits)
est += int32(ofTT.deltaNbBits>>16 + mlTT.deltaNbBits>>16)
// Subtract savings compared to literal encoding...
m.est -= (m.length * bitsPerByte) >> 10
if m.est > 0 {
length := m.length
est -= (length * bitsPerByte) >> 10
if est > 0 {
// Unlikely gain..
m.length = 0
m.est = highScore
est, length = highScore, 0
}
m.est, m.length = est, length
}

func (m *match) ofCode() uint8 {
offset := uint32(m.rep)
if offset < 0 {
offset = uint32(m.s-m.offset) + 3
}
return ofCode(offset)
}

// bestFastEncoder uses 2 tables, one for short matches (5 bytes) and one for long matches.
Expand Down Expand Up @@ -216,7 +218,7 @@ encodeLoop:
}
}
m := match{offset: offset, s: s, length: 4 + e.matchlen(s+4, offset+4, src), rep: rep}
m.estBits(bitsPerByte)
m.estBits(bitsPerByte, m.ofCode(), mlCode(uint32(m.length-zstdMinMatch)))
return m
}

Expand Down