Peter Vreman a écrit :
Compelling FPC 2.1.4 to behave like FPC 2.0.4 is not very difficult.
In a program where you have "A := B - C;" (A,B,C being Longwords), it
is sufficient to write "A := Longword(Longint(B) - Longint(C));" and all
is right. The most difficult is to find which lines of code has to be
modified. FPC signals most of them ("Possible loss of data ...") but not
all. For instance, "if (A and (A-1)) = ..." is silently converted as a
64-bit operation.
But the problem is not just an efficiency problem, it is also a 'result'
problem. For instance, try this with both FPC 2.0.4 and 2.1.4 :
B := 1111;
C := 1112;
D := 311;
A := (B - C) div D;
You will get two different values for A.
With 2.0.4, you compute ((B - C) mod 2^32) div D; with 2.1.4, you
compute (B - C) div D where (B - C) is a 64-bit signed parameter. These
are two different operations.
We did a lot of experiments regarding this. There is no clear description how
to calculate the
longwords.
The only thing that is clear in all that stuff, this is the situation :
we inherit the mess initiated by Borland in the 80's. If, at that time,
someone at Borland decided to follow some standard (the ADA one, for
instance), today things would certainly be a little less lame.
The current behavior of 2.1.4 is the best effort we could do that is both the
same on 32-bit and
64-bit platforms. In 2.0.4 there was a difference between 32-bit and 64-bit
platforms and fpc was
also not always compatible with delphi.
I understand that your work is not easy, there is no good solution.
Either you follow Borland, i.e., you go on with the current mess, or you
try to rationalize things but, in this case, you can no more be fully
compatible with what was previously done.
mm
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