Function ApplySortComparator

src/include/utils/sortsupport.h:199–230

* Apply a sort comparator function and return a 3-way comparison result. * This takes care of handling reverse-sort and NULLs-ordering properly. */

 * This takes care of handling reverse-sort and NULLs-ordering properly.
 */
static inline int
ApplySortComparator(Datum datum1, bool isNull1,
					Datum datum2, bool isNull2,
					SortSupport ssup)
{
	int			compare;

	if (isNull1)
	{
		if (isNull2)
			compare = 0;		/* NULL "=" NULL */
		else if (ssup->ssup_nulls_first)
			compare = -1;		/* NULL "<" NOT_NULL */
		else
			compare = 1;		/* NULL ">" NOT_NULL */
	}
	else if (isNull2)
	{
		if (ssup->ssup_nulls_first)
			compare = 1;		/* NOT_NULL ">" NULL */
		else
			compare = -1;		/* NOT_NULL "<" NULL */
	}
	else
	{
		compare = ssup->comparator(datum1, datum2, ssup);
		if (ssup->ssup_reverse)
			INVERT_COMPARE_RESULT(compare);
	}

	return compare;
}

/*
 * Apply a sort comparator function and return a 3-way comparison using full,