Remove old bitvector
License: MIT Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>
This commit is contained in:
Jakub Sztandera
Jakub Sztandera
parent
01c0a6ec9f
commit
794490c490
@ -1,229 +0,0 @@
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package bitvector
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import (
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"errors"
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"log"
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)
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var (
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// ErrOutOfRange - the index passed is out of range for the BitVector
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ErrOutOfRange = errors.New("index out of range")
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)
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// BitNumbering indicates the ordering of bits, either
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// least-significant bit in position 0, or most-significant bit
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// in position 0.
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//
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// It it used in 3 ways with BitVector:
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// 1. Ordering of bits within the Buf []byte structure
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// 2. What order to add bits when using Extend()
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// 3. What order to read bits when using Take()
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//
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// https://en.wikipedia.org/wiki/Bit_numbering
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type BitNumbering int
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const (
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// LSB0 - bit ordering starts with the low-order bit
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LSB0 BitNumbering = iota
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// MSB0 - bit ordering starts with the high-order bit
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MSB0
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)
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// BitVector is used to manipulate ordered collections of bits
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type BitVector struct {
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Buf []byte
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// BytePacking is the bit ordering within bytes
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BytePacking BitNumbering
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// Len is the logical number of bits in the vector.
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// The last byte in Buf may have undefined bits if Len is not a multiple of 8
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Len uint
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}
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// NewBitVector constructs a new BitVector from a slice of bytes.
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//
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// The bytePacking parameter is required to know how to interpret the bit ordering within the bytes.
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func NewBitVector(buf []byte, bytePacking BitNumbering) *BitVector {
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return &BitVector{
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BytePacking: bytePacking,
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Buf: buf,
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Len: uint(len(buf) * 8),
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}
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}
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// Push adds a single bit to the BitVector.
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//
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// Although it takes a byte, only the low-order bit is used, so just use 0 or 1.
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func (v *BitVector) Push(val byte) {
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if v.Len%8 == 0 {
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v.Buf = append(v.Buf, 0)
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}
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lastIdx := v.Len / 8
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switch v.BytePacking {
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case LSB0:
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v.Buf[lastIdx] |= (val & 1) << (v.Len % 8)
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default:
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v.Buf[lastIdx] |= (val & 1) << (7 - (v.Len % 8))
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}
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v.Len++
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}
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// Get returns a single bit as a byte -- either 0 or 1
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func (v *BitVector) Get(idx uint) (byte, error) {
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if idx >= v.Len {
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return 0, ErrOutOfRange
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}
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blockIdx := idx / 8
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switch v.BytePacking {
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case LSB0:
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return v.Buf[blockIdx] >> (idx % 8) & 1, nil
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default:
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return v.Buf[blockIdx] >> (7 - idx%8) & 1, nil
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}
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}
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// Extend adds up to 8 bits to the receiver
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//
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// Given a byte b == 0b11010101
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// v.Extend(b, 4, LSB0) would add < 1, 0, 1, 0 >
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// v.Extend(b, 4, MSB0) would add < 1, 1, 0, 1 >
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//
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// Panics if count is out of range
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func (v *BitVector) Extend(val byte, count uint, order BitNumbering) {
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if count > 8 {
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log.Panicf("invalid count")
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}
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for i := uint(0); i < count; i++ {
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switch order {
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case LSB0:
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v.Push((val >> i) & 1)
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default:
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v.Push((val >> (7 - i)) & 1)
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}
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}
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}
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// Take reads up to 8 bits at the given index.
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//
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// Given a BitVector < 1, 1, 0, 1, 0, 1, 0, 1 >
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// v.Take(0, 4, LSB0) would return 0b00001011
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// v.Take(0, 4, MSB0) would return 0b11010000
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//
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// Panics if count is out of range
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func (v *BitVector) Take(index uint, count uint, order BitNumbering) (out byte) {
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if count > 8 {
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log.Panicf("invalid count")
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}
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if order == LSB0 && v.BytePacking == LSB0 {
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x := index >> 3
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r := index & 7
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var o uint16
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l := uint(len(v.Buf))
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if x+1 < l {
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o = uint16(v.Buf[x]) | uint16(v.Buf[x+1])<<8
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} else if x < l {
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o = uint16(v.Buf[x])
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}
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o = o >> r
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return byte(o & (0xFF >> (8 - count)))
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}
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for i := uint(0); i < count; i++ {
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val, _ := v.Get(index + i)
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switch order {
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case LSB0:
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out |= val << i
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default:
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out |= val << (7 - i)
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}
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}
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return
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}
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var masks = [9]byte{
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0x0,
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0x1,
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0x3,
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0x7,
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0xF,
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0x1F,
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0x3F,
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0x7F,
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0xFF,
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}
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// Iterator returns a function, which when invoked, returns the number
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// of bits requested, and increments an internal cursor.
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//
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// When the end of the BitVector is reached, it returns zeroes indefinitely
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//
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// Panics if count is out of range
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func (v *BitVector) Iterator(order BitNumbering) func(uint) byte {
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if order == LSB0 && v.BytePacking == LSB0 {
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// Here be dragons
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// This is about 10x faster
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index := int(0)
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var rest uint64
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for n := 7; n >= 0; n-- {
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var o uint64
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if len(v.Buf) > n {
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o = uint64(v.Buf[n])
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}
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rest = rest<<8 | o
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index++
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}
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bitCap := uint(64)
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return func(bits uint) (out byte) {
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if bits > 8 {
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log.Panicf("invalid count")
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}
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res := byte(rest) & masks[bits]
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rest = rest >> bits
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bitCap = bitCap - bits
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if bitCap < 8 {
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var add uint64
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for n := 6; n >= 0; n-- {
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var o uint64
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if len(v.Buf) > index+n {
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o = uint64(v.Buf[index+n])
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}
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add = add<<8 | o
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}
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index = index + 7
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rest = rest | add<<(bitCap)
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bitCap = bitCap + 7*8
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}
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return res
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}
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} else {
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cursor := uint(0)
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return func(count uint) (out byte) {
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if count > 8 {
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log.Panicf("invalid count")
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}
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out = v.Take(cursor, count, order)
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cursor += count
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return
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}
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}
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}
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@ -1,153 +0,0 @@
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package bitvector_test
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import (
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"runtime"
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"testing"
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"github.com/stretchr/testify/assert"
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bitvector "github.com/filecoin-project/go-lotus/lib/rlepluslazy/internal"
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)
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func TestBitVector(t *testing.T) {
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t.Run("zero value", func(t *testing.T) {
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var v bitvector.BitVector
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assert.Equal(t, bitvector.LSB0, v.BytePacking)
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})
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t.Run("Push", func(t *testing.T) {
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// MSB0 bit numbering
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v := bitvector.BitVector{BytePacking: bitvector.MSB0}
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v.Push(1)
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v.Push(0)
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v.Push(1)
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v.Push(1)
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assert.Equal(t, byte(176), v.Buf[0])
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// LSB0 bit numbering
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v = bitvector.BitVector{BytePacking: bitvector.LSB0}
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v.Push(1)
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v.Push(0)
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v.Push(1)
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v.Push(1)
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assert.Equal(t, byte(13), v.Buf[0])
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})
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t.Run("Get", func(t *testing.T) {
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bits := []byte{1, 0, 1, 1, 0, 0, 1, 0}
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for _, numbering := range []bitvector.BitNumbering{bitvector.MSB0, bitvector.LSB0} {
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v := bitvector.BitVector{BytePacking: numbering}
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for _, bit := range bits {
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v.Push(bit)
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}
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for idx, expected := range bits {
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actual, _ := v.Get(uint(idx))
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assert.Equal(t, expected, actual)
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}
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}
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})
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t.Run("Extend", func(t *testing.T) {
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val := byte(171) // 0b10101011
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var v bitvector.BitVector
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// MSB0 bit numbering
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v = bitvector.BitVector{}
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v.Extend(val, 4, bitvector.MSB0)
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assertBitVector(t, []byte{1, 0, 1, 0}, v)
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v.Extend(val, 5, bitvector.MSB0)
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assertBitVector(t, []byte{1, 0, 1, 0, 1, 0, 1, 0, 1}, v)
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// LSB0 bit numbering
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v = bitvector.BitVector{}
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v.Extend(val, 4, bitvector.LSB0)
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assertBitVector(t, []byte{1, 1, 0, 1}, v)
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v.Extend(val, 5, bitvector.LSB0)
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assertBitVector(t, []byte{1, 1, 0, 1, 1, 1, 0, 1, 0}, v)
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})
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t.Run("invalid counts to Take/Extend/Iterator cause panics", func(t *testing.T) {
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v := bitvector.BitVector{BytePacking: bitvector.LSB0}
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assert.Panics(t, func() { v.Extend(0xff, 9, bitvector.LSB0) })
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assert.Panics(t, func() { v.Take(0, 9, bitvector.LSB0) })
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next := v.Iterator(bitvector.LSB0)
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assert.Panics(t, func() { next(9) })
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})
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t.Run("Take", func(t *testing.T) {
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var v bitvector.BitVector
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bits := []byte{1, 0, 1, 0, 1, 0, 1, 1}
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for _, bit := range bits {
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v.Push(bit)
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}
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assert.Equal(t, byte(176), v.Take(4, 4, bitvector.MSB0))
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assert.Equal(t, byte(13), v.Take(4, 4, bitvector.LSB0))
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})
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t.Run("Iterator", func(t *testing.T) {
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var buf []byte
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// make a bitvector of 256 sample bits
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for i := 0; i < 1000; i++ {
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buf = append(buf, byte(i))
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}
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v := bitvector.NewBitVector(buf, bitvector.LSB0)
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next := v.Iterator(bitvector.LSB0)
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// compare to Get()
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for i := uint(0); i < v.Len; i++ {
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expected, _ := v.Get(i)
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assert.Equal(t, expected, next(1), "at index %d", i)
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}
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// out of range should return zero
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assert.Equal(t, byte(0), next(1))
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assert.Equal(t, byte(0), next(8))
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// compare to Take()
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next = v.Iterator(bitvector.LSB0)
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assert.Equal(t, next(5), v.Take(0, 5, bitvector.LSB0))
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assert.Equal(t, next(8), v.Take(5, 8, bitvector.LSB0))
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})
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}
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// Note: When using this helper assertion, expectedBits should *only* be 0s and 1s.
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func assertBitVector(t *testing.T, expectedBits []byte, actual bitvector.BitVector) {
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assert.Equal(t, uint(len(expectedBits)), actual.Len)
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for idx, bit := range expectedBits {
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actualBit, err := actual.Get(uint(idx))
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assert.NoError(t, err)
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assert.Equal(t, bit, actualBit)
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}
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}
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func BenchmarkTake(b *testing.B) {
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buf := make([]byte, 0, 128)
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for i := 0; i < 128; i++ {
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buf = append(buf, byte(128+i))
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}
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v := bitvector.NewBitVector(buf, bitvector.LSB0)
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b.ReportAllocs()
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b.ResetTimer()
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next := v.Iterator(bitvector.LSB0)
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for i := 0; i < b.N; i++ {
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runtime.KeepAlive(next(8))
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}
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}
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