Function enum_cmp_internal

src/backend/utils/adt/enum.c:245–297

* enum_cmp_internal is the common engine for all the visible comparison * functions, except for enum_eq and enum_ne which can just check for OID * equality directly. */

 * equality directly.
 */
static int
enum_cmp_internal(Oid arg1, Oid arg2, FunctionCallInfo fcinfo)
{
	TypeCacheEntry *tcache;

	/*
	 * We don't need the typcache except in the hopefully-uncommon case that
	 * one or both Oids are odd.  This means that cursory testing of code that
	 * fails to pass flinfo to an enum comparison function might not disclose
	 * the oversight.  To make such errors more obvious, Assert that we have a
	 * place to cache even when we take a fast-path exit.
	 */
	Assert(fcinfo->flinfo != NULL);

	/* Equal OIDs are equal no matter what */
	if (arg1 == arg2)
		return 0;

	/* Fast path: even-numbered Oids are known to compare correctly */
	if ((arg1 & 1) == 0 && (arg2 & 1) == 0)
	{
		if (arg1 < arg2)
			return -1;
		else
			return 1;
	}

	/* Locate the typcache entry for the enum type */
	tcache = (TypeCacheEntry *) fcinfo->flinfo->fn_extra;
	if (tcache == NULL)
	{
		HeapTuple	enum_tup;
		Form_pg_enum en;
		Oid			typeoid;

		/* Get the OID of the enum type containing arg1 */
		enum_tup = SearchSysCache1(ENUMOID, ObjectIdGetDatum(arg1));
		if (!HeapTupleIsValid(enum_tup))
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_BINARY_REPRESENTATION),
					 errmsg("invalid internal value for enum: %u",
							arg1)));
		en = (Form_pg_enum) GETSTRUCT(enum_tup);
		typeoid = en->enumtypid;
		ReleaseSysCache(enum_tup);
		/* Now locate and remember the typcache entry */
		tcache = lookup_type_cache(typeoid, 0);
		fcinfo->flinfo->fn_extra = (void *) tcache;
	}

	/* The remaining comparison logic is in typcache.c */
	return compare_values_of_enum(tcache, arg1, arg2);
}

Datum
enum_lt(PG_FUNCTION_ARGS)