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Newsgroups: comp.lang.ada
Date: Mon, 21 May 2018 17:58:45 -0700 (PDT)
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Subject: Re: Should exceeding the range of Integer wrap around a la C?
From: "Dan'l Miller" <optikos@verizon.net>
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Xref: reader02.eternal-september.org comp.lang.ada:52562
Date: 2018-05-21T17:58:45-07:00
List-Id: <comp.lang.ada>

On Monday, May 21, 2018 at 7:39:54 PM UTC-5, Jere wrote:
> On Monday, May 21, 2018 at 3:11:45 PM UTC-4, Paul Rubin wrote:
> > > Should exceeding the range of Integer wrap around a la C?
> > SNIPPED..
> >=20
> > In C, unsigned integer overflow is undefined behaviour, like a subscrip=
t
> > overflow.  Wraparound is one common result because of how machine
> > arithmetic works, but it is not guaranteed.  The program could instead
> > crash, or delete your files, or anything else.  See here:
> >=20
> > http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html
>=20
> Just wanted to point this out because I think you have a typo, but=20
> overflow for unsigned integers is completely defined in the C standard.
> It is considered wraparound logic [1].  Signed integer overflow is=20
> undefined behavior however.
>=20
> [1] Section 6.2.5/9 of the C11 standard

Yes, it has been there for quite some time, all the way back to ANSI C in 1=
989, IIRC.  P.J. Plaugher was the main driver of modulo arithmetic as the s=
ound theoretical basis of unsigned integer types' overflow (and underflow b=
elow zero).  Standard C has a different concept of byte though:  sometimes =
8-bit, sometimes 9-bit, sometimes 16-bit, sometimes 32-bit.  So =E2=80=A2wh=
en=E2=80=A2 an unsigned char overflows to wrap around back to zero via modu=
lo arithmetic can vary per target hardware ISA.