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float_encoder_iterator.go
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/
float_encoder_iterator.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 (
"math"
"github.com/m3db/m3/src/dbnode/encoding"
)
// FloatEncoderAndIterator encapsulates the state required for a logical stream of bits
// that represent a stream of float values compressed with XOR.
type FloatEncoderAndIterator struct {
PrevXOR uint64
PrevFloatBits uint64
// Only taken into account if using the WriteFloat() and ReadFloat()
// APIs.
NotFirst bool
}
// WriteFloat writes a float into the stream, writing the full value or a compressed
// XOR as appropriate.
func (eit *FloatEncoderAndIterator) WriteFloat(stream encoding.OStream, val float64) {
fb := math.Float64bits(val)
if eit.NotFirst {
eit.writeNextFloat(stream, fb)
} else {
eit.writeFullFloat(stream, fb)
eit.NotFirst = true
}
}
// ReadFloat reads a compressed float from the stream.
func (eit *FloatEncoderAndIterator) ReadFloat(stream encoding.IStream) error {
if eit.NotFirst {
return eit.readNextFloat(stream)
}
err := eit.readFullFloat(stream)
eit.NotFirst = true
return err
}
func (eit *FloatEncoderAndIterator) writeFullFloat(stream encoding.OStream, val uint64) {
eit.PrevFloatBits = val
eit.PrevXOR = val
stream.WriteBits(val, 64)
}
func (eit *FloatEncoderAndIterator) writeNextFloat(stream encoding.OStream, val uint64) {
xor := eit.PrevFloatBits ^ val
eit.writeXOR(stream, xor)
eit.PrevXOR = xor
eit.PrevFloatBits = val
}
func (eit *FloatEncoderAndIterator) writeXOR(stream encoding.OStream, currXOR uint64) {
if currXOR == 0 {
stream.WriteBits(opcodeZeroValueXOR, 1)
return
}
// NB(xichen): can be further optimized by keeping track of leading and trailing zeros in eit.
prevLeading, prevTrailing := encoding.LeadingAndTrailingZeros(eit.PrevXOR)
curLeading, curTrailing := encoding.LeadingAndTrailingZeros(currXOR)
if curLeading >= prevLeading && curTrailing >= prevTrailing {
stream.WriteBits(opcodeContainedValueXOR, 2)
stream.WriteBits(currXOR>>uint(prevTrailing), 64-prevLeading-prevTrailing)
return
}
stream.WriteBits(opcodeUncontainedValueXOR, 2)
stream.WriteBits(uint64(curLeading), 6)
numMeaningfulBits := 64 - curLeading - curTrailing
// numMeaningfulBits is at least 1, so we can subtract 1 from it and encode it in 6 bits
stream.WriteBits(uint64(numMeaningfulBits-1), 6)
stream.WriteBits(currXOR>>uint(curTrailing), numMeaningfulBits)
}
func (eit *FloatEncoderAndIterator) readFullFloat(stream encoding.IStream) error {
vb, err := stream.ReadBits(64)
if err != nil {
return err
}
eit.PrevFloatBits = vb
eit.PrevXOR = vb
return nil
}
func (eit *FloatEncoderAndIterator) readNextFloat(stream encoding.IStream) error {
cb, err := stream.ReadBits(1)
if err != nil {
return err
}
if cb == opcodeZeroValueXOR {
eit.PrevXOR = 0
eit.PrevFloatBits ^= eit.PrevXOR
return nil
}
nextCB, err := stream.ReadBits(1)
if err != nil {
return err
}
cb = (cb << 1) | nextCB
if cb == opcodeContainedValueXOR {
previousLeading, previousTrailing := encoding.LeadingAndTrailingZeros(eit.PrevXOR)
numMeaningfulBits := 64 - previousLeading - previousTrailing
meaningfulBits, err := stream.ReadBits(numMeaningfulBits)
if err != nil {
return err
}
eit.PrevXOR = meaningfulBits << uint(previousTrailing)
eit.PrevFloatBits ^= eit.PrevXOR
return nil
}
numLeadingZeros, err := stream.ReadBits(6)
if err != nil {
return err
}
numMeaningfulBits, err := stream.ReadBits(6)
if err != nil {
return err
}
numMeaningfulBits = numMeaningfulBits + 1
meaningfulBits, err := stream.ReadBits(int(numMeaningfulBits))
if err != nil {
return err
}
numTrailingZeros := 64 - numLeadingZeros - numMeaningfulBits
eit.PrevXOR = meaningfulBits << uint(numTrailingZeros)
eit.PrevFloatBits ^= eit.PrevXOR
return nil
}