Simple map-backed bitset in Go

bitset.go

package bitset

import "errors"

// BitSet represents a set of booleans.
type BitSet struct {
	buckets map[int]byte
}

// New creates a new BitSet.
func New() *BitSet {
	return &BitSet{make(map[int]byte)}
}

// Set sets the bit at the given location to the given value. For example,
// bitset.Set(18, true) sets the bit at the position 18 to 1.
func (b *BitSet) Set(pos int, value bool) {
	if pos < 0 {
		panic(errors.New("index out of range"))
	}

	index := pos / 8
	bit := uint(pos % 8)
	current, ok := b.buckets[index]
	if value {
		current = current | (1 << bit)
	} else {
		current = current &^ (1 << bit)
	}
	if current != 0 {
		b.buckets[index] = current
	} else if ok {
		delete(b.buckets, index)
	}
}

// Get reads the bit value at the given position.
func (b *BitSet) Get(pos int) bool {
	if pos < 0 {
		panic(errors.New("index out of range"))
	}

	index := pos / 8
	bit := uint(pos % 8)
	if ((b.buckets[index] >> bit) & 1) == 1 {
		return true
	}
	return false
}

// ToSlice returns a slice containing all the bit positions that are set to 1.
func (b *BitSet) ToSlice() (slice []int) {
	for index, value := range b.buckets {
		bit := 0
		for value > 0 {
			if (value & 1) == 1 {
				slice = append(slice, index*8+bit)
			}
			bit++
			value = value >> 1
		}
	}
	return slice
}