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bitarray.go
149 lines (128 loc) · 3.79 KB
/
bitarray.go
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/*
* Copyright 2018 Insolar
*
* 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 packets
import (
"bytes"
"encoding/binary"
"math"
"github.com/pkg/errors"
)
const sizeOfBlock = 8
type bitArray struct {
array []uint8
bitsSize int
}
func round(dividend, divider int) float64 {
return math.Round(float64(dividend/divider) + 0.5)
}
func newBitArray(size int) *bitArray {
totalSize := uint64(round(size, sizeOfBlock))
return &bitArray{
array: make([]uint8, totalSize),
bitsSize: int(size),
}
}
func (arr *bitArray) Len() int {
return arr.bitsSize
}
func (arr *bitArray) put(bit, index int) error {
if index >= arr.bitsSize {
return errors.New("[ put ] failed to put a bit. out of range")
}
block := getBlockInBitArray(index)
step := getStepToMove(index)
mask := uint8(1 << step)
if bit == 0 {
arr.array[block] &= ^(mask) // change index bit to 0
} else if bit == 1 {
arr.array[block] |= mask // change index bit to 1
} else {
return errors.New("trying to set a wrong bit value")
}
return nil
}
func (arr *bitArray) serialize(compressed bool) ([]byte, error) {
if compressed {
return arr.serializeCompressed()
}
var result bytes.Buffer
for _, b := range arr.array {
err := binary.Write(&result, defaultByteOrder, b)
if err != nil {
return nil, errors.Wrap(err, "[ serialize] failed to serialize a bitarray")
}
}
return result.Bytes(), nil
}
func (arr *bitArray) serializeCompressed() ([]byte, error) {
var result bytes.Buffer
last, err := arr.getState(0)
if err != nil {
return nil, errors.Wrap(err, "[ serializeCompressed ] failed to get state from bitarray")
}
count := uint8(1)
for i := 1; i < arr.bitsSize/2; i++ { // cuz 2 bits == 1 state
current, err := arr.getState(i)
if err != nil {
return nil, errors.Wrap(err, "[ serializeCompressed ] failed to get state from bitarray")
}
if (last != current) || (i+1 >= arr.bitsSize/2) {
count++
err := binary.Write(&result, binary.BigEndian, count)
if err != nil {
return nil, errors.Wrap(err, "[ serializeCompressed ] failed to write to buffer")
}
err = binary.Write(&result, binary.BigEndian, last)
if err != nil {
return nil, errors.Wrap(err, "[ serializeCompressed ] failed to write to buffer")
}
count = 0
last = current
} else {
count++
}
}
return result.Bytes(), nil
}
func (arr *bitArray) get(index int) (uint8, error) {
if index >= arr.bitsSize {
return 0, errors.New("failed to get a bit - index out of range")
}
block := getBlockInBitArray(index)
step := getStepToMove(index)
res := arr.array[block] >> step // get bit by index from block
return res & lastBitMask, nil
}
func (arr *bitArray) getState(index int) (uint8, error) {
if index >= arr.bitsSize {
return 0, errors.New("failed to get a bit - index out of range")
}
stateFirstBit, err := arr.get(2 * index)
if err != nil {
return 0, errors.Wrap(err, "[ getState ] failed to get a bit from bitarray")
}
stateSecondBit, err := arr.get(2*index + 1)
if err != nil {
return 0, errors.Wrap(err, "[ getState ] failed to get a bit from bitarray")
}
return (stateFirstBit << 1) + stateSecondBit, nil
}
func getStepToMove(index int) uint8 {
return uint8(sizeOfBlock - index%sizeOfBlock - 1)
}
func getBlockInBitArray(index int) uint8 {
return uint8(index / sizeOfBlock)
}