fix andSparseWithDenseBitArray resulting array trimming

Author: bcicen

bitarray/and.go

@@ -71,6 +71,10 @@ func andSparseWithSparseBitArray(sba, other *sparseBitArray) BitArray {
 }
 
 func andSparseWithDenseBitArray(sba *sparseBitArray, other *bitArray) BitArray {
+	if other.IsEmpty() {
+		return newSparseBitArray()
+	}
+
 	// Use a duplicate of the sparse array to store the results of the
 	// bitwise and. More memory-efficient than allocating a new dense bit
 	// array.
@@ -83,14 +87,14 @@ func andSparseWithDenseBitArray(sba *sparseBitArray, other *bitArray) BitArray {
 
 	// Run through the sparse array and attempt comparisons wherever
 	// possible against the dense bit array.
-	for selfIndex, selfValue := range sba.indices {
+	for selfIndex, selfValue := range ba.indices {
 
 		if selfValue >= uint64(len(other.blocks)) {
 			// The dense bit array has been exhausted. This is the
 			// annoying case because we have to trim the sparse
 			// array to the size of the dense array.
-			ba.blocks = ba.blocks[:selfIndex]
-			ba.indices = ba.indices[:selfIndex]
+			ba.blocks = ba.blocks[:selfIndex-1]
+			ba.indices = ba.indices[:selfIndex-1]
 
 			// once this is done, there are no more comparisons.
 			// We're ready to return
@@ -99,9 +103,15 @@ func andSparseWithDenseBitArray(sba *sparseBitArray, other *bitArray) BitArray {
 		ba.blocks[selfIndex] = ba.blocks[selfIndex].and(
 			other.blocks[selfValue])
 
-		if ba.blocks[selfIndex] == 0 {
-			ba.blocks.deleteAtIndex(int64(selfIndex))
-			ba.indices.deleteAtIndex(int64(selfIndex))
+	}
+
+	// Ensure any zero'd blocks in the resulting sparse
+	// array are deleted
+	for i := 0; i < len(ba.blocks); i++ {
+		if ba.blocks[i] == 0 {
+			ba.blocks.deleteAtIndex(int64(i))
+			ba.indices.deleteAtIndex(int64(i))
+			i--
 		}
 	}