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zstd: Increase speed on incompressible data for best #314

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Feb 5, 2021
Merged

zstd: Increase speed on incompressible data for best #314

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10 changes: 6 additions & 4 deletions zstd/enc_best.go
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ func (e *bestFastEncoder) Encode(blk *blockEnc, src []byte) {
// Override src
src = e.hist
sLimit := int32(len(src)) - inputMargin
const kSearchStrength = 12
const kSearchStrength = 10

// nextEmit is where in src the next emitLiteral should start from.
nextEmit := s
Expand Down Expand Up @@ -186,9 +186,11 @@ encodeLoop:
best = bestOf(best, matchAt(s-offset1+1, s+1, uint32(cv>>8), 1))
best = bestOf(best, matchAt(s-offset2+1, s+1, uint32(cv>>8), 2))
best = bestOf(best, matchAt(s-offset3+1, s+1, uint32(cv>>8), 3))
best = bestOf(best, matchAt(s-offset1+3, s+3, uint32(cv>>24), 1))
best = bestOf(best, matchAt(s-offset2+3, s+3, uint32(cv>>24), 2))
best = bestOf(best, matchAt(s-offset3+3, s+3, uint32(cv>>24), 3))
if best.length > 0 {
best = bestOf(best, matchAt(s-offset1+3, s+3, uint32(cv>>24), 1))
best = bestOf(best, matchAt(s-offset2+3, s+3, uint32(cv>>24), 2))
best = bestOf(best, matchAt(s-offset3+3, s+3, uint32(cv>>24), 3))
}
}
// Load next and check...
e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: candidateL.offset}
Expand Down
2 changes: 1 addition & 1 deletion zstd/enc_fast.go
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Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,7 @@ func (e *fastEncoder) Encode(blk *blockEnc, src []byte) {
// TEMPLATE
const hashLog = tableBits
// seems global, but would be nice to tweak.
const kSearchStrength = 8
const kSearchStrength = 7

// nextEmit is where in src the next emitLiteral should start from.
nextEmit := s
Expand Down
2 changes: 1 addition & 1 deletion zstd/encoder_test.go
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Expand Up @@ -1024,7 +1024,7 @@ func BenchmarkRandom10MBEncodeAllFastest(b *testing.B) {
rng := rand.New(rand.NewSource(1))
data := make([]byte, 10<<20)
rng.Read(data)
enc, _ := NewWriter(nil, WithEncoderLevel(SpeedFastest), WithEncoderConcurrency(1))
enc, _ := NewWriter(nil, WithEncoderLevel(SpeedFastest), WithEncoderConcurrency(2))
defer enc.Close()
dst := enc.EncodeAll(data, nil)
wantSize := len(dst)
Expand Down