[fpc-pascal]mixed cardinal/signed operations
jonas at zeus.rug.ac.be
Wed Dec 13 19:53:00 CET 2000
As of tomorrow, the fixes branch snapshot (and as such also the
soon-to-be-released 1.0.4) will evaluate divisions which contain a
cardinal (unsigned 32bit integer) and a signed expression by first
converting both arguments to int64 and then performing the operation with
64bits of precision. The result of such an operation will be an int64 as
The reason is that if you have
l := -1;
d := 1;
writeln(l div d);
the program will currently terminate with a division by zero error (the
actual error is a division overflow, but the errorcode is the same).
This 64bit evaluation will also be used for addition, substraction and
multiplication (if the above operand conditions are fulfilled) when range
and/or overflow checking is used. A warning will be issued in all cases.
In general, you won't notice this (except that this 64bit operation is
obviously a lot slower than a normal 32bit one), except if you typecast
the result back to a pointer, because an int64 can't be converted to a
pointer. In that case, either add another typecast to dword/longint in
between, or (preferably) typecase all operands of the oepration to either
longint or dword so no 64bit evaluation is necessary.
BTW: if someone thinks this 64bit evaluation should be the default for
all mathematical operations regardless of whether range and/or overflow
checking is enabled, please speak up, because we aren't 100% sure
ourselves of how this should be handled.
More information about the fpc-pascal