The following program behaves differently under 32-bit and 64-bit compilation. In 64-bit the "max()" function returns a large integer when a value is sent out of bounds (output not shown). The point of the max() is to keep a value from going out of bounds. This problem does not occur in 32-bit code. To make sure that range checking was on in both cases I set "a" out of range after the max().
Is this a feature of the cpu option? And/or is there a more robust way of keeping within range?
Thanks for any help.
P.S. I've already received the following response from Frank.
I'm not using a 64 bit machine myself, so I can only speculate. I hope Waldek can say more about it.
I think the problem might be that GPC treats "arange" internally as an unsigned type (i.e., as a subrange of "Cardinal", not "Integer") and on the 64 bit machine performs the "a - 1" unsigned which causes the range error. (On the 32 bit machine it can do it in LongestInt which covers the range of "Cardinal" as well as negative values, but on 64 bit, it currently doesn't support larger integer types. This might explain the different behaviour.)
Of course, this is a GPC bug as, according to ISO, your program is perfectly valid (given a suitable definition of "Max" which isn't part of ISO).
So the bugfix might be to make subrange types signed when the range allows (which would always be the case in valid ISO programs).
Frank
-------------------- program test(input,output);
type arange = 0..5;
var a,b : arange;
begin a:= 0; b := max(a-1,0); /* keep b in range */ writeln('here ',b,' now really go out of range '); a := b-1; /* take a out of range to make sure range checking is on */ writeln('there ',a); end.
--------------------
Output
32-bit: here 0 now really go out of range a.out: value out of range (error #300 at 180e3)
64-bit a.out: value out of range (error #300 at 100009d2b)
32-bit compilation gpc maxtest.pas
64-bit gpc $g64pth $m64opt maxtest.pas
where $m64opt= "-mcpu=ultrasparc3 -m64"
--------------------- Here is the version output
hpc1014@sfnode0$ gpc -v Reading specs from /opt/gpc/20051104/lib/gcc/sparc-sun-solaris2.10/3.4.3/specs Configured with: ../gcc-3.4.3/configure --prefix=/opt/gpc/20051104 --enable-languages=pascal Thread model: posix gpc version 20051104, based on gcc-3.4.3
-- Chris Christopher Ferrall http://econ.queensu.ca/%7Eferrall/ Associate Professor of Economics Department of Economics http://www.econ.queensu.ca Queen's University http://www.queensu.ca Kingston, Ontario CANADA K7L 3N6 ferrallc AT post.queensu.ca Mackintosh-Corry Rm A519 ph: 613-533-6658 fx: 613-533-6668