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bit_array.go
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378 lines (342 loc) · 7.77 KB
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package common
import (
"encoding/binary"
"fmt"
"regexp"
"strings"
"sync"
)
type BitArray struct {
mtx sync.Mutex
Bits int `json:"bits"` // NOTE: persisted via reflect, must be exported
Elems []uint64 `json:"elems"` // NOTE: persisted via reflect, must be exported
}
// There is no BitArray whose Size is 0. Use nil instead.
func NewBitArray(bits int) *BitArray {
if bits <= 0 {
return nil
}
return &BitArray{
Bits: bits,
Elems: make([]uint64, (bits+63)/64),
}
}
func (bA *BitArray) Size() int {
if bA == nil {
return 0
}
return bA.Bits
}
// NOTE: behavior is undefined if i >= bA.Bits
func (bA *BitArray) GetIndex(i int) bool {
if bA == nil {
return false
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
return bA.getIndex(i)
}
func (bA *BitArray) getIndex(i int) bool {
if i >= bA.Bits {
return false
}
return bA.Elems[i/64]&(uint64(1)<<uint(i%64)) > 0
}
// NOTE: behavior is undefined if i >= bA.Bits
func (bA *BitArray) SetIndex(i int, v bool) bool {
if bA == nil {
return false
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
return bA.setIndex(i, v)
}
func (bA *BitArray) setIndex(i int, v bool) bool {
if i >= bA.Bits {
return false
}
if v {
bA.Elems[i/64] |= (uint64(1) << uint(i%64))
} else {
bA.Elems[i/64] &= ^(uint64(1) << uint(i%64))
}
return true
}
func (bA *BitArray) Copy() *BitArray {
if bA == nil {
return nil
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
return bA.copy()
}
func (bA *BitArray) copy() *BitArray {
c := make([]uint64, len(bA.Elems))
copy(c, bA.Elems)
return &BitArray{
Bits: bA.Bits,
Elems: c,
}
}
func (bA *BitArray) copyBits(bits int) *BitArray {
c := make([]uint64, (bits+63)/64)
copy(c, bA.Elems)
return &BitArray{
Bits: bits,
Elems: c,
}
}
// Returns a BitArray of larger bits size.
func (bA *BitArray) Or(o *BitArray) *BitArray {
if bA == nil && o == nil {
return nil
}
if bA == nil && o != nil {
return o.Copy()
}
if o == nil {
return bA.Copy()
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
c := bA.copyBits(MaxInt(bA.Bits, o.Bits))
for i := 0; i < len(c.Elems); i++ {
c.Elems[i] |= o.Elems[i]
}
return c
}
// Returns a BitArray of smaller bit size.
func (bA *BitArray) And(o *BitArray) *BitArray {
if bA == nil || o == nil {
return nil
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
return bA.and(o)
}
func (bA *BitArray) and(o *BitArray) *BitArray {
c := bA.copyBits(MinInt(bA.Bits, o.Bits))
for i := 0; i < len(c.Elems); i++ {
c.Elems[i] &= o.Elems[i]
}
return c
}
func (bA *BitArray) Not() *BitArray {
if bA == nil {
return nil // Degenerate
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
c := bA.copy()
for i := 0; i < len(c.Elems); i++ {
c.Elems[i] = ^c.Elems[i]
}
return c
}
func (bA *BitArray) Sub(o *BitArray) *BitArray {
if bA == nil || o == nil {
// TODO: Decide if we should do 1's complement here?
return nil
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
if bA.Bits > o.Bits {
c := bA.copy()
for i := 0; i < len(o.Elems)-1; i++ {
c.Elems[i] &= ^c.Elems[i]
}
i := len(o.Elems) - 1
if i >= 0 {
for idx := i * 64; idx < o.Bits; idx++ {
// NOTE: each individual GetIndex() call to o is safe.
c.setIndex(idx, c.getIndex(idx) && !o.GetIndex(idx))
}
}
return c
}
return bA.and(o.Not()) // Note degenerate case where o == nil
}
func (bA *BitArray) IsEmpty() bool {
if bA == nil {
return true // should this be opposite?
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
for _, e := range bA.Elems {
if e > 0 {
return false
}
}
return true
}
func (bA *BitArray) IsFull() bool {
if bA == nil {
return true
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
// Check all elements except the last
for _, elem := range bA.Elems[:len(bA.Elems)-1] {
if (^elem) != 0 {
return false
}
}
// Check that the last element has (lastElemBits) 1's
lastElemBits := (bA.Bits+63)%64 + 1
lastElem := bA.Elems[len(bA.Elems)-1]
return (lastElem+1)&((uint64(1)<<uint(lastElemBits))-1) == 0
}
func (bA *BitArray) PickRandom() (int, bool) {
if bA == nil {
return 0, false
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
length := len(bA.Elems)
if length == 0 {
return 0, false
}
randElemStart := RandIntn(length)
for i := 0; i < length; i++ {
elemIdx := ((i + randElemStart) % length)
if elemIdx < length-1 {
if bA.Elems[elemIdx] > 0 {
randBitStart := RandIntn(64)
for j := 0; j < 64; j++ {
bitIdx := ((j + randBitStart) % 64)
if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
return 64*elemIdx + bitIdx, true
}
}
PanicSanity("should not happen")
}
} else {
// Special case for last elem, to ignore straggler bits
elemBits := bA.Bits % 64
if elemBits == 0 {
elemBits = 64
}
randBitStart := RandIntn(elemBits)
for j := 0; j < elemBits; j++ {
bitIdx := ((j + randBitStart) % elemBits)
if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
return 64*elemIdx + bitIdx, true
}
}
}
}
return 0, false
}
// String returns a string representation of BitArray: BA{<bit-string>},
// where <bit-string> is a sequence of 'x' (1) and '_' (0).
// The <bit-string> includes spaces and newlines to help people.
// For a simple sequence of 'x' and '_' characters with no spaces or newlines,
// see the MarshalJSON() method.
// Example: "BA{_x_}" or "nil-BitArray" for nil.
func (bA *BitArray) String() string {
return bA.StringIndented("")
}
func (bA *BitArray) StringIndented(indent string) string {
if bA == nil {
return "nil-BitArray"
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
return bA.stringIndented(indent)
}
func (bA *BitArray) stringIndented(indent string) string {
lines := []string{}
bits := ""
for i := 0; i < bA.Bits; i++ {
if bA.getIndex(i) {
bits += "x"
} else {
bits += "_"
}
if i%100 == 99 {
lines = append(lines, bits)
bits = ""
}
if i%10 == 9 {
bits += indent
}
if i%50 == 49 {
bits += indent
}
}
if len(bits) > 0 {
lines = append(lines, bits)
}
return fmt.Sprintf("BA{%v:%v}", bA.Bits, strings.Join(lines, indent))
}
func (bA *BitArray) Bytes() []byte {
bA.mtx.Lock()
defer bA.mtx.Unlock()
numBytes := (bA.Bits + 7) / 8
bytes := make([]byte, numBytes)
for i := 0; i < len(bA.Elems); i++ {
elemBytes := [8]byte{}
binary.LittleEndian.PutUint64(elemBytes[:], bA.Elems[i])
copy(bytes[i*8:], elemBytes[:])
}
return bytes
}
// NOTE: other bitarray o is not locked when reading,
// so if necessary, caller must copy or lock o prior to calling Update.
// If bA is nil, does nothing.
func (bA *BitArray) Update(o *BitArray) {
if bA == nil || o == nil {
return
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
copy(bA.Elems, o.Elems)
}
// MarshalJSON implements json.Marshaler interface by marshaling bit array
// using a custom format: a string of '-' or 'x' where 'x' denotes the 1 bit.
func (bA *BitArray) MarshalJSON() ([]byte, error) {
if bA == nil {
return []byte("null"), nil
}
bA.mtx.Lock()
defer bA.mtx.Unlock()
bits := `"`
for i := 0; i < bA.Bits; i++ {
if bA.getIndex(i) {
bits += `x`
} else {
bits += `_`
}
}
bits += `"`
return []byte(bits), nil
}
var bitArrayJSONRegexp = regexp.MustCompile(`\A"([_x]*)"\z`)
// UnmarshalJSON implements json.Unmarshaler interface by unmarshaling a custom
// JSON description.
func (bA *BitArray) UnmarshalJSON(bz []byte) error {
b := string(bz)
if b == "null" {
// This is required e.g. for encoding/json when decoding
// into a pointer with pre-allocated BitArray.
bA.Bits = 0
bA.Elems = nil
return nil
}
// Validate 'b'.
match := bitArrayJSONRegexp.FindStringSubmatch(b)
if match == nil {
return fmt.Errorf("BitArray in JSON should be a string of format %q but got %s", bitArrayJSONRegexp.String(), b)
}
bits := match[1]
// Construct new BitArray and copy over.
numBits := len(bits)
bA2 := NewBitArray(numBits)
for i := 0; i < numBits; i++ {
if bits[i] == 'x' {
bA2.SetIndex(i, true)
}
}
*bA = *bA2
return nil
}