Add Reset method to Bitmap.

Useful for fully clearing bitmap efficiently without reallocation.

PiperOrigin-RevId: 646125349

pkg/bitmap/bitmap.go

@@ -250,6 +250,14 @@ func (b *Bitmap) FlipRange(begin, end uint32) {
 	}
 }
 
+// Reset zeroes the entire bitmap.
+func (b *Bitmap) Reset() {
+	b.numOnes = 0
+	for i := range b.bitBlock {
+		b.bitBlock[i] = 0
+	}
+}
+
 // ForEach calls `f` for each set bit in the range [start, end).
 //
 // If f returns false, ForEach stops the iteration.

pkg/bitmap/bitmap_test.go

@@ -292,6 +292,13 @@ func TestBitmapNumOnes(t *testing.T) {
 	if bitmapOnes != uint32(20) {
 		t.Errorf("After ClearRange, GetNumOnes() returns: %v, wanted: %v", bitmapOnes, 20)
 	}
+
+	// Reset to fully clear bitmap.
+	bitmap.Reset()
+	bitmapOnes = bitmap.GetNumOnes()
+	if bitmapOnes != uint32(0) {
+		t.Errorf("After Reset, GetNumOnes() returns: %v, wanted: %v", bitmapOnes, 0)
+	}
 }
 
 type bitmapForEachTestcase struct {