m3tsz.go

// Copyright (c) 2016 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 (
	"errors"
	"math"
)

const (
	// DefaultIntOptimizationEnabled is the default switch for m3tsz int optimization
	DefaultIntOptimizationEnabled = true

	// OpcodeZeroSig indicates that there were zero significant digits.
	OpcodeZeroSig = 0x0
	// OpcodeNonZeroSig indicates that there were a non-zero number of significant digits.
	OpcodeNonZeroSig = 0x1

	// NumSigBits is the number of bits required to encode the maximum possible value
	// of significant digits.
	NumSigBits = 6

	opcodeZeroValueXOR        = 0x0
	opcodeContainedValueXOR   = 0x2
	opcodeUncontainedValueXOR = 0x3
	opcodeNoUpdateSig         = 0x0
	opcodeUpdateSig           = 0x1
	opcodeUpdate              = 0x0
	opcodeNoUpdate            = 0x1
	opcodeUpdateMult          = 0x1
	opcodeNoUpdateMult        = 0x0
	opcodePositive            = 0x0
	opcodeNegative            = 0x1
	opcodeRepeat              = 0x1
	opcodeNoRepeat            = 0x0
	opcodeFloatMode           = 0x1
	opcodeIntMode             = 0x0

	sigDiffThreshold   = uint8(3)
	sigRepeatThreshold = uint8(5)

	maxMult     = uint8(6)
	numMultBits = 3
)

var (
	maxInt               = float64(math.MaxInt64)
	minInt               = float64(math.MinInt64)
	maxOptInt            = math.Pow(10.0, 13) // Max int for int optimization
	multipliers          = createMultipliers()
	errInvalidMultiplier = errors.New("supplied multiplier is invalid")
)

// convertToIntFloat takes a float64 val and the current max multiplier
// and attempts to transform the float into an int with multiplier. There
// is potential for a small accuracy loss for float values that are very
// close to ints eg. 46.000000000000001 would be returned as 46. This only
// applies to values where the next possible smaller or larger float changes
// the integer component of the float
func convertToIntFloat(v float64, curMaxMult uint8) (float64, uint8, bool, error) {
	if curMaxMult == 0 && v < maxInt {
		// Quick check for vals that are already ints
		i, r := math.Modf(v)
		if r == 0 {
			return i, 0, false, nil
		}
	}

	if curMaxMult > maxMult {
		return 0.0, 0, false, errInvalidMultiplier
	}

	val := v * multipliers[int(curMaxMult)]
	sign := 1.0
	if v < 0 {
		sign = -1.0
		val = val * -1.0
	}

	for mult := curMaxMult; mult <= maxMult && val < maxOptInt; mult++ {
		i, r := math.Modf(val)
		if r == 0 {
			return sign * i, mult, false, nil
		} else if r < 0.1 {
			// Round down and check
			if math.Nextafter(val, 0) <= i {
				return sign * i, mult, false, nil
			}
		} else if r > 0.9 {
			// Round up and check
			next := i + 1
			if math.Nextafter(val, next) >= next {
				return sign * next, mult, false, nil
			}
		}
		val = val * 10.0
	}

	return v, 0, true, nil
}

func convertFromIntFloat(val float64, mult uint8) float64 {
	if mult == 0 {
		return val
	}

	return val / multipliers[int(mult)]
}

// createMultipliers creates all the multipliers up to maxMult
// and places them into a slice
func createMultipliers() []float64 {
	multipliers := make([]float64, maxMult+1)
	base := 1.0
	for i := 0; i <= int(maxMult); i++ {
		multipliers[i] = base
		base = base * 10.0
	}

	return multipliers
}