nomad: adding simple bitmap implementation

nomad/structs/bitmap.go

@@ -0,0 +1,39 @@
+package structs
+
+import "fmt"
+
+// Bitmap is a simple uncompressed bitmap
+type Bitmap []byte
+
+// NewBitmap returns a bitmap with up to size indexes
+func NewBitmap(size int) (Bitmap, error) {
+	if size <= 0 {
+		return nil, fmt.Errorf("bitmap must be positive size")
+	}
+	if size&7 != 0 {
+		return nil, fmt.Errorf("bitmap must be byte aligned")
+	}
+	b := make([]byte, size>>3)
+	return Bitmap(b), nil
+}
+
+// Set is used to set the given index of the bitmap
+func (b Bitmap) Set(idx uint) {
+	bucket := idx >> 3
+	mask := byte(1 << (idx & 7))
+	b[bucket] |= mask
+}
+
+// Check is used to check the given index of the bitmap
+func (b Bitmap) Check(idx uint) bool {
+	bucket := idx >> 3
+	mask := byte(1 << (idx & 7))
+	return (b[bucket] & mask) != 0
+}
+
+// Clear is used to efficiently clear the bitmap
+func (b Bitmap) Clear() {
+	for i := range b {
+		b[i] = 0
+	}
+}

nomad/structs/bitmap_test.go

@@ -0,0 +1,58 @@
+package structs
+
+import "testing"
+
+func TestBitmap(t *testing.T) {
+	// Check invalid sizes
+	_, err := NewBitmap(0)
+	if err == nil {
+		t.Fatalf("bad")
+	}
+	_, err = NewBitmap(7)
+	if err == nil {
+		t.Fatalf("bad")
+	}
+
+	// Create a normal bitmap
+	b, err := NewBitmap(256)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	// Set a few bits
+	b.Set(0)
+	b.Set(255)
+
+	// Verify the bytes
+	if b[0] == 0 {
+		t.Fatalf("bad")
+	}
+	if !b.Check(0) {
+		t.Fatalf("bad")
+	}
+
+	// Verify the bytes
+	if b[len(b)-1] == 0 {
+		t.Fatalf("bad")
+	}
+	if !b.Check(255) {
+		t.Fatalf("bad")
+	}
+
+	// All other bits should be unset
+	for i := 1; i < 255; i++ {
+		if b.Check(uint(i)) {
+			t.Fatalf("bad")
+		}
+	}
+
+	// Clear
+	b.Clear()
+
+	// All bits should be unset
+	for i := 0; i < 256; i++ {
+		if b.Check(uint(i)) {
+			t.Fatalf("bad")
+		}
+	}
+}