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// Copyright 2020, Chef. All rights reserved.
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// https://github.com/q191201771/naza
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//
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// Use of this source code is governed by a MIT-style license
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// that can be found in the License file.
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//
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// Author: Chef (191201771@qq.com)
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package nazabits
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// TODO
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// - 这个package的性能可以优化
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// - BitReader考虑增加skip接口
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// - BitReader开率增加返回目前位置接口
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// 所有的读写操作，由调用方保证不超出切片的范围
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type BitReader struct {
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core []byte
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index uint
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pos uint // 从左往右
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}
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func NewBitReader(b []byte) BitReader {
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return BitReader{
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core: b,
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}
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}
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func (br *BitReader) ReadBit() uint8 {
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res := GetBit8(br.core[br.index], 7-br.pos)
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br.pos++
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if br.pos == 8 {
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br.pos = 0
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br.index++
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}
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return res
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}
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// @param n: 取值范围 [1, 8]
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func (br *BitReader) ReadBits8(n uint) (r uint8) {
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for i := uint(0); i < n; i++ {
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r = (r << 1) | br.ReadBit()
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}
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return
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}
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// @param n: 取值范围 [1, 16]
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func (br *BitReader) ReadBits16(n uint) (r uint16) {
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for i := uint(0); i < n; i++ {
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r = (r << 1) | uint16(br.ReadBit())
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}
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return
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}
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func (br *BitReader) ReadBits32(n uint) (r uint32) {
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for i := uint(0); i < n; i++ {
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r = (r << 1) | uint32(br.ReadBit())
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}
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return
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}
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// @param n: 读取多少个字节
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func (br *BitReader) ReadBytes(n uint) (r []byte) {
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for i := uint(0); i < n; i++ {
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r = append(r, br.ReadBits8(8))
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}
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return
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}
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// ----------------------------------------------------------------------------
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type BitWriter struct {
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core []byte
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index int
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pos uint // 从左往右
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}
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func NewBitWriter(b []byte) BitWriter {
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return BitWriter{
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core: b,
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}
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}
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// @param b: 当b不为0和1时，取b的最低位
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func (bw *BitWriter) WriteBit(b uint8) {
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bw.core[bw.index] |= (b & 0x1) << (7 - bw.pos)
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bw.pos++
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if bw.pos == 8 {
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bw.pos = 0
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bw.index++
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}
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}
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// 将<v>的低<n>位写入
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// @param n: 取值范围 [1, 8]
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func (bw *BitWriter) WriteBits8(n uint, v uint8) {
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for i := n - 1; ; i-- {
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bw.WriteBit(v >> i & 0x1)
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if i == 0 {
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break
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}
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}
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}
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func (bw *BitWriter) WriteBits16(n uint, v uint16) {
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for i := n - 1; ; i-- {
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bw.WriteBit(uint8(v >> i & 0x1))
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if i == 0 {
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break
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}
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}
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}
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// ----------------------------------------------------------------------------
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// @param pos: 取值范围 [0, 7]，0表示最低位
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func GetBit8(v uint8, pos uint) uint8 {
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return GetBits8(v, pos, 1)
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}
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// @param pos: 取值范围 [0, 7]，0表示最低位
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// @param n: 取多少位， 取值范围 [1, 8]
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//
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// 举例，GetBits8(105, 2, 4) = 10（即1010）
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// v: 0110 1001
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// pos: 2
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// n: .. ..
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//
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func GetBits8(v uint8, pos uint, n uint) uint8 {
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return v >> pos & m[n]
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}
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func GetBit16(v []byte, pos uint) uint8 {
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if pos < 8 {
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return GetBit8(v[1], pos)
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}
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return GetBit8(v[0], pos-8)
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}
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func GetBits16(v []byte, pos uint, n uint) uint16 {
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if pos < 8 {
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if pos+n < 9 {
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return uint16(GetBits8(v[1], pos, n))
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}
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return uint16(GetBits8(v[1], pos, 8-pos)) | uint16(GetBits8(v[0], 0, pos+n-8))<<(8-pos)
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}
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return uint16(GetBits8(v[0], pos-8, n))
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}
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var m []uint8
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func init() {
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m = []uint8{0, 1, 3, 7, 15, 31, 63, 127, 255} // 0 is dummy
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}
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