79 lines
1.7 KiB
Go
79 lines
1.7 KiB
Go
package structs
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import "fmt"
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// Bitmap is a simple uncompressed bitmap
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type Bitmap []byte
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// NewBitmap returns a bitmap with up to size indexes
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func NewBitmap(size uint) (Bitmap, error) {
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if size == 0 {
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return nil, fmt.Errorf("bitmap must be positive size")
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}
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if size&7 != 0 {
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return nil, fmt.Errorf("bitmap must be byte aligned")
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}
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b := make([]byte, size>>3)
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return Bitmap(b), nil
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}
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// Copy returns a copy of the Bitmap
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func (b Bitmap) Copy() (Bitmap, error) {
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if b == nil {
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return nil, fmt.Errorf("can't copy nil Bitmap")
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}
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raw := make([]byte, len(b))
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copy(raw, b)
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return Bitmap(raw), nil
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}
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// Size returns the size of the bitmap
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func (b Bitmap) Size() uint {
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return uint(len(b) << 3)
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}
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// Set is used to set the given index of the bitmap
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func (b Bitmap) Set(idx uint) {
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bucket := idx >> 3
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mask := byte(1 << (idx & 7))
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b[bucket] |= mask
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}
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// Unset is used to unset the given index of the bitmap
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func (b Bitmap) Unset(idx uint) {
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bucket := idx >> 3
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// Mask should be all ones minus the idx position
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offset := 1 << (idx & 7)
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mask := byte(offset ^ 0xff)
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b[bucket] &= mask
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}
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// Check is used to check the given index of the bitmap
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func (b Bitmap) Check(idx uint) bool {
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bucket := idx >> 3
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mask := byte(1 << (idx & 7))
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return (b[bucket] & mask) != 0
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}
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// Clear is used to efficiently clear the bitmap
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func (b Bitmap) Clear() {
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for i := range b {
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b[i] = 0
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}
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}
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// IndexesInRange returns the indexes in which the values are either set or unset based
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// on the passed parameter in the passed range
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func (b Bitmap) IndexesInRange(set bool, from, to uint) []int {
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var indexes []int
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for i := from; i <= to && i < b.Size(); i++ {
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c := b.Check(i)
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if c && set || !c && !set {
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indexes = append(indexes, int(i))
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}
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}
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return indexes
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}
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