github.com/m3db/m3@v1.5.0/src/dbnode/encoding/m3tsz/int_sig_bits_tracker.go (about)

     1  // Copyright (c) 2019 Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  package m3tsz
    22  
    23  import "github.com/m3db/m3/src/dbnode/encoding"
    24  
    25  // IntSigBitsTracker is used to track the number of significant bits
    26  // which should be used to encode the delta between two integers.
    27  type IntSigBitsTracker struct {
    28  	NumSig             uint8 // current largest number of significant places for int diffs
    29  	CurHighestLowerSig uint8
    30  	NumLowerSig        uint8
    31  }
    32  
    33  // WriteIntValDiff writes the provided val diff bits along with
    34  // whether the bits are negative or not.
    35  func (t *IntSigBitsTracker) WriteIntValDiff(
    36  	stream encoding.OStream, valBits uint64, neg bool) {
    37  	if neg {
    38  		stream.WriteBit(opcodeNegative)
    39  	} else {
    40  		stream.WriteBit(opcodePositive)
    41  	}
    42  
    43  	stream.WriteBits(valBits, int(t.NumSig))
    44  }
    45  
    46  // WriteIntSig writes the number of significant bits of the diff if it has changed and
    47  // updates the IntSigBitsTracker.
    48  func (t *IntSigBitsTracker) WriteIntSig(stream encoding.OStream, sig uint8) {
    49  	if t.NumSig != sig {
    50  		stream.WriteBit(opcodeUpdateSig)
    51  		if sig == 0 {
    52  			stream.WriteBit(OpcodeZeroSig)
    53  		} else {
    54  			stream.WriteBit(OpcodeNonZeroSig)
    55  			stream.WriteBits(uint64(sig-1), NumSigBits)
    56  		}
    57  	} else {
    58  		stream.WriteBit(opcodeNoUpdateSig)
    59  	}
    60  
    61  	t.NumSig = sig
    62  }
    63  
    64  // TrackNewSig gets the new number of significant bits given the
    65  // number of significant bits of the current diff. It takes into
    66  // account thresholds to try and find a value that's best for the
    67  // current data
    68  func (t *IntSigBitsTracker) TrackNewSig(numSig uint8) uint8 {
    69  	newSig := t.NumSig
    70  
    71  	if numSig > t.NumSig {
    72  		newSig = numSig
    73  	} else if t.NumSig-numSig >= sigDiffThreshold {
    74  		if t.NumLowerSig == 0 {
    75  			t.CurHighestLowerSig = numSig
    76  		} else if numSig > t.CurHighestLowerSig {
    77  			t.CurHighestLowerSig = numSig
    78  		}
    79  
    80  		t.NumLowerSig++
    81  		if t.NumLowerSig >= sigRepeatThreshold {
    82  			newSig = t.CurHighestLowerSig
    83  			t.NumLowerSig = 0
    84  		}
    85  
    86  	} else {
    87  		t.NumLowerSig = 0
    88  	}
    89  
    90  	return newSig
    91  }