partialmessages: add basic bitmap package

The bitmap is probably the common case, so add library support for it.

Author: MarcoPolo

partialmessages/bitmap/bitmap.go

@@ -0,0 +1,84 @@
+package bitmap
+
+import (
+	"math/bits"
+)
+
+type Bitmap []byte
+
+func NewBitmapWithOnesCount(n int) Bitmap {
+	b := make(Bitmap, (n+7)/8)
+	for i := range n {
+		b.Set(i)
+	}
+	return b
+}
+
+func Merge(left, right Bitmap) Bitmap {
+	out := make(Bitmap, max(len(left), len(right)))
+	out.Or(left)
+	out.Or(right)
+	return out
+}
+
+func (b Bitmap) IsZero() bool {
+	for i := range b {
+		if b[i] != 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func (b Bitmap) OnesCount() int {
+	var count int
+	for i := range b {
+		count += bits.OnesCount8(b[i])
+	}
+	return count
+}
+
+func (b Bitmap) Set(index int) {
+	for len(b)*8 <= index {
+		b = append(b, 0)
+	}
+	b[index/8] |= 1 << (uint(index) % 8)
+}
+
+func (b Bitmap) Get(index int) bool {
+	if index >= len(b)*8 {
+		return false
+	}
+	return b[index/8]&(1<<(uint(index%8))) != 0
+}
+
+func (b Bitmap) Clear(index int) {
+	if index >= len(b)*8 {
+		return
+	}
+	b[index/8] &^= 1 << (uint(index) % 8)
+}
+
+func (b Bitmap) And(other Bitmap) {
+	for i := range min(len(b), len(other)) {
+		b[i] &= other[i]
+	}
+}
+
+func (b Bitmap) Or(other Bitmap) {
+	for i := range min(len(b), len(other)) {
+		b[i] |= other[i]
+	}
+}
+
+func (b Bitmap) Xor(other Bitmap) {
+	for i := range min(len(b), len(other)) {
+		b[i] ^= other[i]
+	}
+}
+
+func (b Bitmap) Flip() {
+	for i := range b {
+		b[i] ^= 0xff
+	}
+}