Merge pull request #438 from zoltanmeze/fix-previous-value

Fix previousValue not returning correct results in some cases

roaring.go

@@ -1935,13 +1935,14 @@ func (rb *Bitmap) PreviousValue(target uint32) int64 {
 	}
 
 	if rb.highlowcontainer.getKeyAtIndex(containerIndex) > originalKey {
-		return -1
+		// target absent, key of first container after target too high
+		containerIndex--
 	}
 
 	for containerIndex != -1 && prevValue == -1 {
 		containerKey := rb.highlowcontainer.getKeyAtIndex(containerIndex)
 		container := rb.highlowcontainer.getContainer(containerKey)
-		// if containerKey > orginalKey then we are past the container which mapped to the orignal key
+		// if containerKey > originalKey then we are past the container which mapped to the original key
 		// in that case we can just return the minimum from that container
 		var responseBit int
 		if containerKey < originalKey {

roaring_test.go

@@ -2973,6 +2973,17 @@ func TestNextAndPreviousValue(t *testing.T) {
 		}
 	})
 
+	t.Run("Absent target container", func(t *testing.T) {
+		bmp := BitmapOf(2, 3, 131072, MaxUint32)
+
+		assert.Equal(t, int64(3), bmp.PreviousValue(65536))
+		assert.Equal(t, int64(131072), bmp.PreviousValue(MaxUint32>>1))
+		assert.Equal(t, int64(131072), bmp.PreviousValue(MaxUint32-131071))
+
+		bmp = BitmapOf(131072)
+		assert.Equal(t, int64(-1), bmp.PreviousValue(65536))
+	})
+
 	t.Run("skipping with ranges", func(t *testing.T) {
 		bmp := New()
 		intervalEnd := 512