Function PrepareSortSupportComparisonShim

src/backend/utils/sort/sortsupport.c:68–87

* Set up a shim function to allow use of an old-style btree comparison * function as if it were a sort support comparator. */

 * function as if it were a sort support comparator.
 */
void
PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup)
{
	SortShimExtra *extra;

	extra = (SortShimExtra *) MemoryContextAlloc(ssup->ssup_cxt,
												 SizeForSortShimExtra(2));

	/* Lookup the comparison function */
	fmgr_info_cxt(cmpFunc, &extra->flinfo, ssup->ssup_cxt);

	/* We can initialize the callinfo just once and re-use it */
	InitFunctionCallInfoData(extra->fcinfo, &extra->flinfo, 2,
							 ssup->ssup_collation, NULL, NULL);
	extra->fcinfo.args[0].isnull = false;
	extra->fcinfo.args[1].isnull = false;

	ssup->ssup_extra = extra;
	ssup->comparator = comparison_shim;
}

/*
 * Look up and call sortsupport function to setup SortSupport comparator;