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Newsgroups: comp.lang.ada
Date: Mon, 25 Aug 2014 05:54:06 -0700 (PDT)
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Subject: Re: Integer Overflow Question.
From: austin.obyrne769@btinternet.com
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Xref: news.eternal-september.org comp.lang.ada:21900
Date: 2014-08-25T05:54:06-07:00
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On Monday, August 25, 2014 1:20:02 PM UTC+1, gautier...@hotmail.com wrote:
> Le lundi 25 ao=FBt 2014 13:21:33 UTC+2, austin.o...@btinternet.com a =E9c=
rit=A0:
>=20
> > I have written two Ada driven ciphers that are complete and have been t=
weaked for the last time.
>=20
> >=20
>=20
> >=20
>=20
> >=20
>=20
> > I have used an early Ada compiler - a Gnat311.p - of about 1995 vintage=
  <=3D Ada-95.
>=20
> >=20
>=20
> >=20
>=20
> >=20
>=20
> > In order that the ciphers can run in 32-bit computers which are still g=
oing to be around for some time despite the availability of the 64-bit oper=
ating system in Windows 8.1 which I also use, I have had to put a bound on =
the maximum integer size output of computations at 2^31 which of course is =
the maximum positive integer that 32-bit computers can handle.
>=20
> >=20
>=20
> >=20
>=20
> >=20
>=20
> > Running the same software that was written for 32-bit computers in the =
 64-bit environment of 8.1 and raising the bar on integer size I thought I =
should be able to do this ok but no - the cipher will still crash if the in=
teger size is greater than 2^31 when I thought I could go up to 2^63.
>=20
> >=20
>=20
> >=20
>=20
> >=20
>=20
> > As it happens this is not a problem crypto wise because the cipher is i=
ndependent of the integer size but I am intrigued that this overflow should=
 still happen.
>=20
> >=20
>=20
> >=20
>=20
> >=20
>=20
> > I am coming to the conclusion that the max integer size than can be use=
d without integer overflow occurring in any computer is a function of the A=
da compiler being used and not the computer operating system???
>=20
>=20
>=20
> This is the case. This is also the case for most software installed (Word=
, Excel,...) which appear in a "C:\Program Files x86" folder. They all run =
in a 32-bit subsystem of your 64-bit system.
>=20
> If you want to know metrics of your Ada numeric types, just display T'Las=
t, T'Size.
>=20
> Now, even on GNAT 32-bit, there are Integer_64 and Unsigned_64 in the Int=
erfaces package. Use them!
>=20
> HTH
>=20
> _________________________=20
>=20
> Gautier's Ada programming=20
>=20
> http://sf.net/users/gdemont

Many,many thanks.  That is very educational to know.  It suits me fine not =
to go any further. My crypto doesn't need it.  It is useful to me to know h=
owever that I have unwittingly used a standard that I can promote with full=
 confidence to users.

Austin O'Byrne