Function numeric_support

src/backend/utils/adt/numeric.c:840–881

* numeric_support() * * Planner support function for the numeric() length coercion function. * * Flatten calls that solely represent increases in allowable precision. * Scale changes mutate every datum, so they are unoptimizable. Some values, * e.g. 1E-1001, can only fit into an unconstrained numeric, so a change from * an unconstrained numeric to any constrained numeric is also unoptimiza

 * an unconstrained numeric to any constrained numeric is also unoptimizable.
 */
Datum
numeric_support(PG_FUNCTION_ARGS)
{
	Node	   *rawreq = (Node *) PG_GETARG_POINTER(0);
	Node	   *ret = NULL;

	if (IsA(rawreq, SupportRequestSimplify))
	{
		SupportRequestSimplify *req = (SupportRequestSimplify *) rawreq;
		FuncExpr   *expr = req->fcall;
		Node	   *typmod;

		Assert(list_length(expr->args) >= 2);

		typmod = (Node *) lsecond(expr->args);

		if (IsA(typmod, Const) && !((Const *) typmod)->constisnull)
		{
			Node	   *source = (Node *) linitial(expr->args);
			int32		old_typmod = exprTypmod(source);
			int32		new_typmod = DatumGetInt32(((Const *) typmod)->constvalue);
			int32		old_scale = (old_typmod - VARHDRSZ) & 0xffff;
			int32		new_scale = (new_typmod - VARHDRSZ) & 0xffff;
			int32		old_precision = (old_typmod - VARHDRSZ) >> 16 & 0xffff;
			int32		new_precision = (new_typmod - VARHDRSZ) >> 16 & 0xffff;

			/*
			 * If new_typmod < VARHDRSZ, the destination is unconstrained;
			 * that's always OK.  If old_typmod >= VARHDRSZ, the source is
			 * constrained, and we're OK if the scale is unchanged and the
			 * precision is not decreasing.  See further notes in function
			 * header comment.
			 */
			if (new_typmod < (int32) VARHDRSZ ||
				(old_typmod >= (int32) VARHDRSZ &&
				 new_scale == old_scale && new_precision >= old_precision))
				ret = relabel_to_typmod(source, new_typmod);
		}
	}

	PG_RETURN_POINTER(ret);
}

/*
 * numeric() -