fix(hll_family): Fixed bug in merge step of PFMERGE command (#4796)

Fixed bug in hllMergeDense that writes to wrong register.

Fixes #4750

Signed-off-by: mkaruza <[email protected]>

Author: mkaruza

src/redis/hyperloglog.c

@@ -1370,8 +1370,7 @@ int64_t pfcountSingle(struct HllBufferPtr hll_ptr) {
 }
 
 /* Merge dense-encoded HLL */
-static void hllMergeDense(uint8_t* max, struct HllBufferPtr to) {
-  uint8_t* registers = max + HLL_HDR_SIZE;
+static void hllMergeDense(uint8_t* registers, struct HllBufferPtr to) {
   uint8_t val;
   struct hllhdr* hll_hdr = (struct hllhdr*)to.hll;
 

src/server/hll_family_test.cc

@@ -166,8 +166,15 @@ TEST_F(HllFamilyTest, MergeToNew) {
 TEST_F(HllFamilyTest, MergeToExisting) {
   EXPECT_EQ(CheckedInt({"pfadd", "key1", "1", "2", "3"}), 1);
   EXPECT_EQ(CheckedInt({"pfadd", "key2", "4", "5"}), 1);
-  EXPECT_EQ(Run({"pfmerge", "key2", "key1"}), "OK");
-  EXPECT_EQ(CheckedInt({"pfcount", "key2"}), 5);
+  EXPECT_EQ(Run({"pfmerge", "key3", "key2", "key1"}), "OK");
+  EXPECT_EQ(CheckedInt({"pfcount", "key3"}), 5);
+  EXPECT_EQ(Run({"pfmerge", "key3", "key3"}), "OK");
+  EXPECT_EQ(CheckedInt({"pfcount", "key3"}), 5);
+  EXPECT_EQ(Run({"pfmerge", "key3"}), "OK");
+  EXPECT_EQ(CheckedInt({"pfcount", "key3"}), 5);
+  EXPECT_EQ(CheckedInt({"pfadd", "key4", "4", "5", "6"}), 1);
+  EXPECT_EQ(Run({"pfmerge", "key3", "key4"}), "OK");
+  EXPECT_EQ(CheckedInt({"pfcount", "key3"}), 6);
 }
 
 TEST_F(HllFamilyTest, MergeNonExisting) {