1 files changed, 77 insertions, 0 deletions
diff --git a/src/backend/nodes/bitmapset.c b/src/backend/nodes/bitmapset.c
index 3b5fb20964e..4c904e03296 100644
--- a/src/backend/nodes/bitmapset.c
+++ b/src/backend/nodes/bitmapset.c
@@ -336,6 +336,83 @@ bms_is_subset(const Bitmapset *a, const Bitmapset *b)
 }
 
 /*
+ * bms_subset_compare - compare A and B for equality/subset relationships
+ *
+ * This is more efficient than testing bms_is_subset in both directions.
+ */
+BMS_Comparison
+bms_subset_compare(const Bitmapset *a, const Bitmapset *b)
+{
+	BMS_Comparison result;
+	int			shortlen;
+	int			longlen;
+	int			i;
+
+	/* Handle cases where either input is NULL */
+	if (a == NULL)
+	{
+		if (b == NULL)
+			return BMS_EQUAL;
+		return bms_is_empty(b) ? BMS_EQUAL : BMS_SUBSET1;
+	}
+	if (b == NULL)
+		return bms_is_empty(a) ? BMS_EQUAL : BMS_SUBSET2;
+	/* Check common words */
+	result = BMS_EQUAL;			/* status so far */
+	shortlen = Min(a->nwords, b->nwords);
+	for (i = 0; i < shortlen; i++)
+	{
+		bitmapword aword = a->words[i];
+		bitmapword bword = b->words[i];
+
+		if ((aword & ~bword) != 0)
+		{
+			/* a is not a subset of b */
+			if (result == BMS_SUBSET1)
+				return BMS_DIFFERENT;
+			result = BMS_SUBSET2;
+		}
+		if ((bword & ~aword) != 0)
+		{
+			/* b is not a subset of a */
+			if (result == BMS_SUBSET2)
+				return BMS_DIFFERENT;
+			result = BMS_SUBSET1;
+		}
+	}
+	/* Check extra words */
+	if (a->nwords > b->nwords)
+	{
+		longlen = a->nwords;
+		for (; i < longlen; i++)
+		{
+			if (a->words[i] != 0)
+			{
+				/* a is not a subset of b */
+				if (result == BMS_SUBSET1)
+					return BMS_DIFFERENT;
+				result = BMS_SUBSET2;
+			}
+		}
+	}
+	else if (a->nwords < b->nwords)
+	{
+		longlen = b->nwords;
+		for (; i < longlen; i++)
+		{
+			if (b->words[i] != 0)
+			{
+				/* b is not a subset of a */
+				if (result == BMS_SUBSET2)
+					return BMS_DIFFERENT;
+				result = BMS_SUBSET1;
+			}
+		}
+	}
+	return result;
+}
+
+/*
  * bms_is_member - is X a member of A?
  */
 bool