normalization.go

// Copyright 2017 The ObjectHash-Proto Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package protohash

import "fmt"

func floatNormalize(originalFloat float64) (string, error) {
	// Special case 0
	// Note that if we allowed f to end up > .5 or == 0, we'd get the same thing.
	if originalFloat == 0 {
		return "+0:", nil
	}

	// Sign
	f := originalFloat
	s := `+`
	if f < 0 {
		s = `-`
		f = -f
	}
	// Exponent
	e := 0
	for f > 1 {
		f /= 2
		e++
	}
	for f <= .5 {
		f *= 2
		e--
	}
	s += fmt.Sprintf("%d:", e)
	// Mantissa
	if f > 1 || f <= .5 {
		return "", fmt.Errorf("Could not normalize float: %f", originalFloat)
	}
	for f != 0 {
		if f >= 1 {
			s += `1`
			f--
		} else {
			s += `0`
		}
		if f >= 1 {
			return "", fmt.Errorf("Could not normalize float: %f", originalFloat)
		}
		if len(s) >= 1000 {
			return "", fmt.Errorf("Could not normalize float: %f", originalFloat)
		}
		f *= 2
	}
	return s, nil
}