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Subject: Odd overflow exception being raised in one-line program
From: Jerry <lanceboyle@qwest.net>
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Date: 2013-01-29T19:49:10-08:00
List-Id: <comp.lang.ada>

A user of the PLplot plotting package, using Ada bindings, has reported an =
overflow exception that has not occurred before. He reports using Fedora ra=
whide which uses gcc 4.8. He reported the conditions surrounding the except=
ion and I used that to make the following program and asked him to report h=
is results. Line 7 of the below program mimics a line in the Ada binding to=
 which his exception points.

The program:


with Ada.Text_IO;   use Ada.Text_IO;
procedure Test_Overflow is
   r : Integer;
   r1 : Long_Float :=3D 0.3;
begin
   Put_Line("Running....");
   r :=3D Integer((r1 * 255.001) - 0.499999999999999);
end Test_Overflow;


His results:


[orion@vmrawhide ~]$ gnatmake Test_Overflow.adb
gcc -c Test_Overflow.adb
Test_Overflow.adb:2:11: warning: file name does not match unit name, should=
 be "test_overflow.adb"
gnatbind -x Test_Overflow.ali
gnatlink Test_Overflow.ali

[orion@vmrawhide ~]$ ./Test_Overflow
Running....

raised CONSTRAINT_ERROR : Test_Overflow.adb:7 overflow check failed


Just for kicks I had him run it with -gnato and he got the same results.

This runs fine on my OS X 10.7.5 running GPL 2011 (20110419). The Ada bindi=
ng in its present form has compiled on presumably numerous other systems, i=
ncluding those of other developers, without this problem. The PLplot user a=
lso reports several other overflow exceptions, all in a code base that has =
never had such problems before.

I investigated other places (18 total) where he is getting an "overflow che=
ck failed" exception. In every case, the indicated line contains a conversi=
on from Long_Float to Integer using the Integer( ) function with a Long_Flo=
at argument. It appears very likely that the exception is happening at ever=
y attempt to make such a conversion.

What am I missing here?

Jerry