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int_sig_bits_tracker.go
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int_sig_bits_tracker.go
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// Copyright (c) 2019 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package m3tsz
import "github.com/m3db/m3/src/dbnode/encoding"
// IntSigBitsTracker is used to track the number of significant bits
// which should be used to encode the delta between two integers.
type IntSigBitsTracker struct {
NumSig uint8 // current largest number of significant places for int diffs
CurHighestLowerSig uint8
NumLowerSig uint8
}
// WriteIntValDiff writes the provided val diff bits along with
// whether the bits are negative or not.
func (t *IntSigBitsTracker) WriteIntValDiff(
stream encoding.OStream, valBits uint64, neg bool) {
if neg {
stream.WriteBit(opcodeNegative)
} else {
stream.WriteBit(opcodePositive)
}
stream.WriteBits(valBits, int(t.NumSig))
}
// WriteIntSig writes the number of significant bits of the diff if it has changed and
// updates the IntSigBitsTracker.
func (t *IntSigBitsTracker) WriteIntSig(stream encoding.OStream, sig uint8) {
if t.NumSig != sig {
stream.WriteBit(opcodeUpdateSig)
if sig == 0 {
stream.WriteBit(OpcodeZeroSig)
} else {
stream.WriteBit(OpcodeNonZeroSig)
stream.WriteBits(uint64(sig-1), NumSigBits)
}
} else {
stream.WriteBit(opcodeNoUpdateSig)
}
t.NumSig = sig
}
// TrackNewSig gets the new number of significant bits given the
// number of significant bits of the current diff. It takes into
// account thresholds to try and find a value that's best for the
// current data
func (t *IntSigBitsTracker) TrackNewSig(numSig uint8) uint8 {
newSig := t.NumSig
if numSig > t.NumSig {
newSig = numSig
} else if t.NumSig-numSig >= sigDiffThreshold {
if t.NumLowerSig == 0 {
t.CurHighestLowerSig = numSig
} else if numSig > t.CurHighestLowerSig {
t.CurHighestLowerSig = numSig
}
t.NumLowerSig++
if t.NumLowerSig >= sigRepeatThreshold {
newSig = t.CurHighestLowerSig
t.NumLowerSig = 0
}
} else {
t.NumLowerSig = 0
}
return newSig
}