Fair enough, but I would like an explanation as to why it's necessary,
because the reason for testing -1 in particular is very unclear, and I
wonder if there's a known misbehaviour with a particular division
function with -1.
Kit
On 11/05/2023 21:27, Wayne Sherman wrote:
On Thu, May 11,
On Thu, May 11, 2023 at 11:42 AM J. Gareth Moreton wrote:
> This is the code block in question (ncnv.pas, starting at line 3397)
The git "blame" function shows who last made changes:
https://gitlab.com/freepascal.org/fpc/source/-/blame/main/compiler/ncnv.pas?page=4#L3396
Most of that code was
This is the code block in question (ncnv.pas, starting at line 3397) -
if anyone can explain why it has to be set up this way, or add comments
to the code, I will be most grateful (it's run for the following node
types: subn, addn, muln, divn, modn, xorn, andn, orn, shln, shrn):
P.S. I found the code that adds the conditional checks; it's
"doremoveinttypeconvs" in the ncnv unit. However, it's very unclear as
to WHY it's doing it as there's no comments around the code block.
Kit
On 11/05/2023 15:39, J. Gareth Moreton via fpc-devel wrote:
It does seem odd. In a
It does seem odd. In a practical sense, the only time I can see -1
being a common input among other random numbers is if it's an error
value, in which case you would most likely do special handling rather
than pass it through a division operation. With the slowdown that comes
from additional
Looks like a rather disadvantageous way to avoid the idiv instruction because x
div -1 = -x and x mod -1 = 0.
I ran a quick benchmark doing a lot of integer divisions where sometimes
(randomly) the divisor was -1. When the occurence was rare enough (~5%) the
performance was not impacted, the
Hi everyone,
I need to ask a question about how division nodes are set up (I'm
looking at possible optimisation techniques). I've written the
following procedure:
procedure DoDivMod(N, D: Integer; out Q, R: Integer);
begin
Q := N div D;
R := N mod D;
end;
Fairly simple and to the
