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413 lines
9.5 KiB
413 lines
9.5 KiB
package common
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import (
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"encoding/binary"
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"fmt"
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"regexp"
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"strings"
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"sync"
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)
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// BitArray is a thread-safe implementation of a bit array.
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type BitArray struct {
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mtx sync.Mutex
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Bits int `json:"bits"` // NOTE: persisted via reflect, must be exported
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Elems []uint64 `json:"elems"` // NOTE: persisted via reflect, must be exported
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}
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// NewBitArray returns a new bit array.
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// It returns nil if the number of bits is zero.
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func NewBitArray(bits int) *BitArray {
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if bits <= 0 {
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return nil
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}
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return &BitArray{
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Bits: bits,
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Elems: make([]uint64, (bits+63)/64),
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}
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}
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// Size returns the number of bits in the bitarray
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func (bA *BitArray) Size() int {
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if bA == nil {
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return 0
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}
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return bA.Bits
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}
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// GetIndex returns the bit at index i within the bit array.
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// The behavior is undefined if i >= bA.Bits
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func (bA *BitArray) GetIndex(i int) bool {
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if bA == nil {
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return false
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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return bA.getIndex(i)
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}
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func (bA *BitArray) getIndex(i int) bool {
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if i >= bA.Bits {
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return false
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}
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return bA.Elems[i/64]&(uint64(1)<<uint(i%64)) > 0
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}
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// SetIndex sets the bit at index i within the bit array.
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// The behavior is undefined if i >= bA.Bits
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func (bA *BitArray) SetIndex(i int, v bool) bool {
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if bA == nil {
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return false
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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return bA.setIndex(i, v)
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}
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func (bA *BitArray) setIndex(i int, v bool) bool {
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if i >= bA.Bits {
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return false
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}
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if v {
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bA.Elems[i/64] |= (uint64(1) << uint(i%64))
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} else {
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bA.Elems[i/64] &= ^(uint64(1) << uint(i%64))
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}
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return true
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}
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// Copy returns a copy of the provided bit array.
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func (bA *BitArray) Copy() *BitArray {
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if bA == nil {
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return nil
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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return bA.copy()
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}
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func (bA *BitArray) copy() *BitArray {
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c := make([]uint64, len(bA.Elems))
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copy(c, bA.Elems)
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return &BitArray{
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Bits: bA.Bits,
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Elems: c,
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}
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}
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func (bA *BitArray) copyBits(bits int) *BitArray {
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c := make([]uint64, (bits+63)/64)
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copy(c, bA.Elems)
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return &BitArray{
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Bits: bits,
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Elems: c,
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}
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}
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// Or returns a bit array resulting from a bitwise OR of the two bit arrays.
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// If the two bit-arrys have different lengths, Or right-pads the smaller of the two bit-arrays with zeroes.
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// Thus the size of the return value is the maximum of the two provided bit arrays.
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func (bA *BitArray) Or(o *BitArray) *BitArray {
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if bA == nil && o == nil {
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return nil
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}
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if bA == nil && o != nil {
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return o.Copy()
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}
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if o == nil {
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return bA.Copy()
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}
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bA.mtx.Lock()
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o.mtx.Lock()
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c := bA.copyBits(MaxInt(bA.Bits, o.Bits))
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smaller := MinInt(len(bA.Elems), len(o.Elems))
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for i := 0; i < smaller; i++ {
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c.Elems[i] |= o.Elems[i]
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}
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bA.mtx.Unlock()
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o.mtx.Unlock()
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return c
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}
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// And returns a bit array resulting from a bitwise AND of the two bit arrays.
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// If the two bit-arrys have different lengths, this truncates the larger of the two bit-arrays from the right.
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// Thus the size of the return value is the minimum of the two provided bit arrays.
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func (bA *BitArray) And(o *BitArray) *BitArray {
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if bA == nil || o == nil {
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return nil
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}
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bA.mtx.Lock()
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o.mtx.Lock()
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defer func() {
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bA.mtx.Unlock()
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o.mtx.Unlock()
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}()
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return bA.and(o)
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}
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func (bA *BitArray) and(o *BitArray) *BitArray {
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c := bA.copyBits(MinInt(bA.Bits, o.Bits))
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for i := 0; i < len(c.Elems); i++ {
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c.Elems[i] &= o.Elems[i]
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}
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return c
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}
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// Not returns a bit array resulting from a bitwise Not of the provided bit array.
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func (bA *BitArray) Not() *BitArray {
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if bA == nil {
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return nil // Degenerate
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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return bA.not()
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}
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func (bA *BitArray) not() *BitArray {
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c := bA.copy()
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for i := 0; i < len(c.Elems); i++ {
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c.Elems[i] = ^c.Elems[i]
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}
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return c
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}
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// Sub subtracts the two bit-arrays bitwise, without carrying the bits.
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// Note that carryless subtraction of a - b is (a and not b).
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// The output is the same as bA, regardless of o's size.
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// If bA is longer than o, o is right padded with zeroes
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func (bA *BitArray) Sub(o *BitArray) *BitArray {
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if bA == nil || o == nil {
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// TODO: Decide if we should do 1's complement here?
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return nil
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}
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bA.mtx.Lock()
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o.mtx.Lock()
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// output is the same size as bA
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c := bA.copyBits(bA.Bits)
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// Only iterate to the minimum size between the two.
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// If o is longer, those bits are ignored.
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// If bA is longer, then skipping those iterations is equivalent
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// to right padding with 0's
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smaller := MinInt(len(bA.Elems), len(o.Elems))
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for i := 0; i < smaller; i++ {
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// &^ is and not in golang
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c.Elems[i] &^= o.Elems[i]
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}
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bA.mtx.Unlock()
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o.mtx.Unlock()
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return c
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}
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// IsEmpty returns true iff all bits in the bit array are 0
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func (bA *BitArray) IsEmpty() bool {
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if bA == nil {
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return true // should this be opposite?
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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for _, e := range bA.Elems {
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if e > 0 {
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return false
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}
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}
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return true
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}
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// IsFull returns true iff all bits in the bit array are 1.
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func (bA *BitArray) IsFull() bool {
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if bA == nil {
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return true
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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// Check all elements except the last
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for _, elem := range bA.Elems[:len(bA.Elems)-1] {
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if (^elem) != 0 {
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return false
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}
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}
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// Check that the last element has (lastElemBits) 1's
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lastElemBits := (bA.Bits+63)%64 + 1
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lastElem := bA.Elems[len(bA.Elems)-1]
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return (lastElem+1)&((uint64(1)<<uint(lastElemBits))-1) == 0
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}
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// PickRandom returns a random index in the bit array, and its value.
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// It uses the global randomness in `random.go` to get this index.
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func (bA *BitArray) PickRandom() (int, bool) {
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if bA == nil {
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return 0, false
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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length := len(bA.Elems)
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if length == 0 {
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return 0, false
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}
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randElemStart := RandIntn(length)
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for i := 0; i < length; i++ {
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elemIdx := ((i + randElemStart) % length)
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if elemIdx < length-1 {
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if bA.Elems[elemIdx] > 0 {
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randBitStart := RandIntn(64)
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for j := 0; j < 64; j++ {
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bitIdx := ((j + randBitStart) % 64)
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if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
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return 64*elemIdx + bitIdx, true
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}
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}
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PanicSanity("should not happen")
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}
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} else {
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// Special case for last elem, to ignore straggler bits
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elemBits := bA.Bits % 64
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if elemBits == 0 {
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elemBits = 64
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}
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randBitStart := RandIntn(elemBits)
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for j := 0; j < elemBits; j++ {
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bitIdx := ((j + randBitStart) % elemBits)
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if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
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return 64*elemIdx + bitIdx, true
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}
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}
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}
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}
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return 0, false
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}
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// String returns a string representation of BitArray: BA{<bit-string>},
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// where <bit-string> is a sequence of 'x' (1) and '_' (0).
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// The <bit-string> includes spaces and newlines to help people.
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// For a simple sequence of 'x' and '_' characters with no spaces or newlines,
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// see the MarshalJSON() method.
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// Example: "BA{_x_}" or "nil-BitArray" for nil.
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func (bA *BitArray) String() string {
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return bA.StringIndented("")
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}
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// StringIndented returns the same thing as String(), but applies the indent
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// at every 10th bit, and twice at every 50th bit.
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func (bA *BitArray) StringIndented(indent string) string {
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if bA == nil {
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return "nil-BitArray"
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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return bA.stringIndented(indent)
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}
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func (bA *BitArray) stringIndented(indent string) string {
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lines := []string{}
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bits := ""
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for i := 0; i < bA.Bits; i++ {
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if bA.getIndex(i) {
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bits += "x"
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} else {
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bits += "_"
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}
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if i%100 == 99 {
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lines = append(lines, bits)
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bits = ""
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}
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if i%10 == 9 {
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bits += indent
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}
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if i%50 == 49 {
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bits += indent
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}
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}
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if len(bits) > 0 {
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lines = append(lines, bits)
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}
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return fmt.Sprintf("BA{%v:%v}", bA.Bits, strings.Join(lines, indent))
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}
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// Bytes returns the byte representation of the bits within the bitarray.
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func (bA *BitArray) Bytes() []byte {
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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numBytes := (bA.Bits + 7) / 8
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bytes := make([]byte, numBytes)
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for i := 0; i < len(bA.Elems); i++ {
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elemBytes := [8]byte{}
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binary.LittleEndian.PutUint64(elemBytes[:], bA.Elems[i])
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copy(bytes[i*8:], elemBytes[:])
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}
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return bytes
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}
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// Update sets the bA's bits to be that of the other bit array.
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// The copying begins from the begin of both bit arrays.
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func (bA *BitArray) Update(o *BitArray) {
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if bA == nil || o == nil {
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return
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}
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bA.mtx.Lock()
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o.mtx.Lock()
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defer func() {
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bA.mtx.Unlock()
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o.mtx.Unlock()
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}()
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copy(bA.Elems, o.Elems)
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}
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// MarshalJSON implements json.Marshaler interface by marshaling bit array
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// using a custom format: a string of '-' or 'x' where 'x' denotes the 1 bit.
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func (bA *BitArray) MarshalJSON() ([]byte, error) {
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if bA == nil {
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return []byte("null"), nil
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}
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bA.mtx.Lock()
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defer bA.mtx.Unlock()
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bits := `"`
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for i := 0; i < bA.Bits; i++ {
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if bA.getIndex(i) {
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bits += `x`
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} else {
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bits += `_`
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}
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}
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bits += `"`
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return []byte(bits), nil
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}
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var bitArrayJSONRegexp = regexp.MustCompile(`\A"([_x]*)"\z`)
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// UnmarshalJSON implements json.Unmarshaler interface by unmarshaling a custom
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// JSON description.
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func (bA *BitArray) UnmarshalJSON(bz []byte) error {
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b := string(bz)
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if b == "null" {
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// This is required e.g. for encoding/json when decoding
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// into a pointer with pre-allocated BitArray.
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bA.Bits = 0
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bA.Elems = nil
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return nil
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}
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// Validate 'b'.
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match := bitArrayJSONRegexp.FindStringSubmatch(b)
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if match == nil {
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return fmt.Errorf("BitArray in JSON should be a string of format %q but got %s", bitArrayJSONRegexp.String(), b)
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}
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bits := match[1]
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// Construct new BitArray and copy over.
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numBits := len(bits)
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bA2 := NewBitArray(numBits)
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for i := 0; i < numBits; i++ {
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if bits[i] == 'x' {
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bA2.SetIndex(i, true)
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}
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}
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*bA = *bA2
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return nil
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}
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