Convert confusing macros in multixact.c to static inline functions

The macros were confused about the argument data types. All the
arguments were called 'xid', and some of the macros included casts to
TransactionId, even though the arguments were actually either
MultiXactIds or MultiXactOffsets. It compiles to the same thing,
because TransactionId, MultiXactId and MultiXactOffset are all
typedefs of uint32, but it was highly misleading.

Author: Maxim Orlov <orlovmg@gmail.com>
Discussion: https://www.postgresql.org/message-id/CACG%3DezbLUG-OD1osAW3OchOMxZtdxHh2itYR9Zhh-a13wEBEQw%40mail.gmail.com
Discussion: https://www.postgresql.org/message-id/ff143b24-a093-40da-9833-d36b83726bdf%40iki.fi

Author: hlinnaka

src/backend/access/transam/multixact.c

@@ -108,11 +108,23 @@
 /* We need four bytes per offset */
 #define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset))
 
-#define MultiXactIdToOffsetPage(xid) \
-	((xid) / (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
-#define MultiXactIdToOffsetEntry(xid) \
-	((xid) % (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
-#define MultiXactIdToOffsetSegment(xid) (MultiXactIdToOffsetPage(xid) / SLRU_PAGES_PER_SEGMENT)
+static inline int64
+MultiXactIdToOffsetPage(MultiXactId multi)
+{
+	return multi / MULTIXACT_OFFSETS_PER_PAGE;
+}
+
+static inline int
+MultiXactIdToOffsetEntry(MultiXactId multi)
+{
+	return multi % MULTIXACT_OFFSETS_PER_PAGE;
+}
+
+static inline int
+MultiXactIdToOffsetSegment(MultiXactId multi)
+{
+	return MultiXactIdToOffsetPage(multi) / SLRU_PAGES_PER_SEGMENT;
+}
 
 /*
  * The situation for members is a bit more complex: we store one byte of
@@ -156,30 +168,59 @@
 		((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
 
 /* page in which a member is to be found */
-#define MXOffsetToMemberPage(xid) ((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
-#define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) / SLRU_PAGES_PER_SEGMENT)
+static inline int64
+MXOffsetToMemberPage(MultiXactOffset offset)
+{
+	return offset / MULTIXACT_MEMBERS_PER_PAGE;
+}
+
+static inline int
+MXOffsetToMemberSegment(MultiXactOffset offset)
+{
+	return MXOffsetToMemberPage(offset) / SLRU_PAGES_PER_SEGMENT;
+}
 
 /* Location (byte offset within page) of flag word for a given member */
-#define MXOffsetToFlagsOffset(xid) \
-	((((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) % \
-	  (TransactionId) MULTIXACT_MEMBERGROUPS_PER_PAGE) * \
-	 (TransactionId) MULTIXACT_MEMBERGROUP_SIZE)
-#define MXOffsetToFlagsBitShift(xid) \
-	(((xid) % (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) * \
-	 MXACT_MEMBER_BITS_PER_XACT)
+static inline int
+MXOffsetToFlagsOffset(MultiXactOffset offset)
+{
+	MultiXactOffset group = offset / MULTIXACT_MEMBERS_PER_MEMBERGROUP;
+	int			grouponpg = group % MULTIXACT_MEMBERGROUPS_PER_PAGE;
+	int			byteoff = grouponpg * MULTIXACT_MEMBERGROUP_SIZE;
+
+	return byteoff;
+}
+
+static inline int
+MXOffsetToFlagsBitShift(MultiXactOffset offset)
+{
+	int			member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP;
+	int			bshift = member_in_group * MXACT_MEMBER_BITS_PER_XACT;
+
+	return bshift;
+}
 
 /* Location (byte offset within page) of TransactionId of given member */
-#define MXOffsetToMemberOffset(xid) \
-	(MXOffsetToFlagsOffset(xid) + MULTIXACT_FLAGBYTES_PER_GROUP + \
-	 ((xid) % MULTIXACT_MEMBERS_PER_MEMBERGROUP) * sizeof(TransactionId))
+static inline int
+MXOffsetToMemberOffset(MultiXactOffset offset)
+{
+	int			member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP;
+
+	return MXOffsetToFlagsOffset(offset) +
+		MULTIXACT_FLAGBYTES_PER_GROUP +
+		member_in_group * sizeof(TransactionId);
+}
 
 /* Multixact members wraparound thresholds. */
 #define MULTIXACT_MEMBER_SAFE_THRESHOLD		(MaxMultiXactOffset / 2)
 #define MULTIXACT_MEMBER_DANGER_THRESHOLD	\
 	(MaxMultiXactOffset - MaxMultiXactOffset / 4)
 
-#define PreviousMultiXactId(xid) \
-	((xid) == FirstMultiXactId ? MaxMultiXactId : (xid) - 1)
+static inline MultiXactId
+PreviousMultiXactId(MultiXactId multi)
+{
+	return multi == FirstMultiXactId ? MaxMultiXactId : multi - 1;
+}
 
 /*
  * Links to shared-memory data structures for MultiXact control