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snappy: Use dedicated function for scoring #614

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merged 2 commits into from
Jun 3, 2022
Merged

snappy: Use dedicated function for scoring #614

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a093d8d
snappy: Use dedicated function for scoring
klauspost Jun 2, 2022
a73811f
Simpler
klauspost Jun 2, 2022
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24 changes: 23 additions & 1 deletion s2/encode_best.go
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Original file line number Diff line number Diff line change
Expand Up @@ -370,7 +370,7 @@ func encodeBlockBestSnappy(dst, src []byte) (d int) {
}
offset := m.s - m.offset

return score - emitCopySize(offset, m.length)
return score - emitCopyNoRepeatSize(offset, m.length)
}

matchAt := func(offset, s int, first uint32) match {
Expand Down Expand Up @@ -581,6 +581,28 @@ func emitCopySize(offset, length int) int {
return 2
}

// emitCopyNoRepeatSize returns the size to encode the offset+length
//
// It assumes that:
// 1 <= offset && offset <= math.MaxUint32
// 4 <= length && length <= 1 << 24
func emitCopyNoRepeatSize(offset, length int) int {
if offset >= 65536 {
return 5 + 5*(length/64)
}

// Offset no more than 2 bytes.
if length > 64 {
// Emit remaining as repeats, at least 4 bytes remain.
return 3 + 3*(length/60)
}
if length >= 12 || offset >= 2048 {
return 3
}
// Emit the remaining copy, encoded as 2 bytes.
return 2
}

// emitRepeatSize returns the number of bytes required to encode a repeat.
// Length must be at least 4 and < 1<<24
func emitRepeatSize(offset, length int) int {
Expand Down