implement bitmap

Author: Theodus

bitmap/bitmap.go

@@ -0,0 +1,61 @@
+// Package bitmap contains bitmaps of length 32 and 64 for tracking bool
+// values without the need for arrays or hashing.
+package bitmap
+
+// Bitmap32 tracks 32 bool values within a uint32
+type Bitmap32 uint32
+
+// SetBit returns a Bitmap32 with the bit at the given position set to 1
+func (b Bitmap32) SetBit(pos uint) Bitmap32 {
+	return b | (1 << pos)
+}
+
+// ClearBit returns a Bitmap32 with the bit at the given position set to 0
+func (b Bitmap32) ClearBit(pos uint) Bitmap32 {
+	return b & ^(1 << pos)
+}
+
+// HasBit returns true if the bit at the given position in the Bitmap32 is 1
+func (b Bitmap32) HasBit(pos uint) bool {
+	return (b & (1 << pos)) != 0
+}
+
+// PopCount returns the ammount of bits set to 1 in the Bitmap32
+func (b Bitmap32) PopCount() int {
+	// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
+	b -= (b >> 1) & 0x55555555
+	b = (b>>2)&0x33333333 + b&0x33333333
+	b += b >> 4
+	b &= 0x0f0f0f0f
+	b *= 0x01010101
+	return int(byte(b >> 24))
+}
+
+// Bitmap64 tracks 64 bool values within a uint64
+type Bitmap64 uint64
+
+// SetBit returns a Bitmap64 with the bit at the given position set to 1
+func (b Bitmap64) SetBit(pos uint) Bitmap64 {
+	return b | (1 << pos)
+}
+
+// ClearBit returns a Bitmap64 with the bit at the given position set to 0
+func (b Bitmap64) ClearBit(pos uint) Bitmap64 {
+	return b & ^(1 << pos)
+}
+
+// HasBit returns true if the bit at the given position in the Bitmap64 is 1
+func (b Bitmap64) HasBit(pos uint) bool {
+	return (b & (1 << pos)) != 0
+}
+
+// PopCount returns the ammount of bits set to 1 in the Bitmap64
+func (b Bitmap64) PopCount() int {
+	// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
+	b -= (b >> 1) & 0x5555555555555555
+	b = (b>>2)&0x3333333333333333 + b&0x3333333333333333
+	b += b >> 4
+	b &= 0x0f0f0f0f0f0f0f0f
+	b *= 0x0101010101010101
+	return int(byte(b >> 56))
+}

bitmap/bitmap_test.go

@@ -0,0 +1,64 @@
+package bitmap
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPopCount32(t *testing.T) {
+	b := []uint32{
+		uint32(0x55555555), // 0x55555555 = 01010101 01010101 01010101 01010101
+		uint32(0x33333333), // 0x33333333 = 00110011 00110011 00110011 00110011
+		uint32(0x0F0F0F0F), // 0x0F0F0F0F = 00001111 00001111 00001111 00001111
+		uint32(0x00FF00FF), // 0x00FF00FF = 00000000 11111111 00000000 11111111
+		uint32(0x0000FFFF), // 0x0000FFFF = 00000000 00000000 11111111 11111111
+	}
+	for _, x := range b {
+		assert.Equal(t, 16, Bitmap32(x).PopCount())
+	}
+}
+
+func TestPopCount64(t *testing.T) {
+	b := []uint64{
+		uint64(0x5555555555555555),
+		uint64(0x3333333333333333),
+		uint64(0x0F0F0F0F0F0F0F0F),
+		uint64(0x00FF00FF00FF00FF),
+		uint64(0x0000FFFF0000FFFF),
+	}
+	for _, x := range b {
+		assert.Equal(t, 32, Bitmap64(x).PopCount())
+	}
+}
+
+func TestSetBit(t *testing.T) {
+	m := Bitmap32(0)
+	assert.Equal(t, Bitmap32(0x4), m.SetBit(2))
+}
+
+func TestClearBit(t *testing.T) {
+	m := Bitmap32(0x4)
+	assert.Equal(t, Bitmap32(0), m.ClearBit(2))
+}
+
+func TestHasBit(t *testing.T) {
+	m := Bitmap32(0x55555555)
+	assert.Equal(t, true, m.HasBit(2))
+}
+
+func BenchmarkPopCount32(b *testing.B) {
+	m := Bitmap32(0x33333333)
+	b.ResetTimer()
+	for i := b.N; i > 0; i-- {
+		m.PopCount()
+	}
+}
+
+func BenchmarkPopCount64(b *testing.B) {
+	m := Bitmap64(0x3333333333333333)
+	b.ResetTimer()
+	for i := b.N; i > 0; i-- {
+		m.PopCount()
+	}
+}