RE: Autoconf manual's coverage of signed integer overflow & portability

> -Original Message- > I would like to say the one thing I have not heard through this > discussion is the real reason why the C standards comittee decided > signed overflow as being undefined. All I can think of is they were > thinking of target that do saturation for plus/minus but wrapp

Re: Autoconf manual's coverage of signed integer overflow & portability

Paolo Bonzini <[EMAIL PROTECTED]> writes: > I think this will only confuse the matter. I think it's worth mentioning that integer overflow, in theory at least (we hope not in practice) actually allows that sort of aggressive optimization. However, I've tried to reword the example to make it less

Re: Autoconf manual's coverage of signed integer overflow & portability

Andrew Pinski writes: > > This will always cause a trap on x86, even with -fwrapv so really > -fwrapv has a bug on x86. I will file this bug sometime later > tomorrow. Oh and fixing this bug will actually slow down users > of -fwrapv even more than what it is currently does because > you c

Re: Autoconf manual's coverage of signed integer overflow & portability

Paul Eggert <[EMAIL PROTECTED]> writes: | Here are further patches I checked into the Autoconf documentation to | reflect today's comments (some of which I received privately). Thanks | to all of you. The trickiest bit was documenting one simple way to | reliably detect overflow without converti

Re: Autoconf manual's coverage of signed integer overflow & portability

Andrew Pinski <[EMAIL PROTECTED]> writes: | > | > [EMAIL PROTECTED] (Richard Kenner) writes: | > | > >> >> Many portable C programs assume that signed integer overflow wraps around | > >> >> reliably using two's complement arithmetic. | > >> > | > >> | > >> I was looking for an adjective that m

Re: Autoconf manual's coverage of signed integer overflow & portability

The C Standard says that if a program has signed integer overflow its behavior is undefined, and the undefined behavior can even precede the overflow. To take an extreme example: @c Inspired by Robert Dewar's example in @c (2007-01-01). @exampl

Re: Autoconf manual's coverage of signed integer overflow & portability

The C Standard says that if a program has signed integer overflow its behavior is undefined, and the undefined behavior can even precede the overflow. To take an extreme example: @c Inspired by Robert Dewar's example in @c (2007-01-01). @exampl

Re: Autoconf manual's coverage of signed integer overflow & portability

Andrew Pinski <[EMAIL PROTECTED]> writes: > the one thing I have not heard through this > discussion is the real reason why the C standards comittee decided > signed overflow as being undefined. I wasn't there, but my impression is that many of the optimization issues we've talked about in this t

Re: Autoconf manual's coverage of signed integer overflow & portability

> > Here are further patches I checked into the Autoconf documentation to > reflect today's comments (some of which I received privately). Thanks > to all of you. The trickiest bit was documenting one simple way to > reliably detect overflow without converting to unsigned and back. > (At least,

Re: Autoconf manual's coverage of signed integer overflow & portability

> > [EMAIL PROTECTED] (Richard Kenner) writes: > > >> >> Many portable C programs assume that signed integer overflow wraps > >> >> around > >> >> reliably using two's complement arithmetic. > >> > > >> > >> I was looking for an adjective that mean the programs work on a wide > >> variety of pla

Re: Autoconf manual's coverage of signed integer overflow & portability

Here are further patches I checked into the Autoconf documentation to reflect today's comments (some of which I received privately). Thanks to all of you. The trickiest bit was documenting one simple way to reliably detect overflow without converting to unsigned and back. (At least, I hope it's r

Re: Autoconf manual's coverage of signed integer overflow & portability

[EMAIL PROTECTED] (Richard Kenner) writes: >> >> Many portable C programs assume that signed integer overflow wraps around >> >> reliably using two's complement arithmetic. >> > >> >> I was looking for an adjective that mean the programs work on a wide >> variety of platforms, and "portable" seems

Re: Autoconf manual's coverage of signed integer overflow & portability

Andrew Pinski <[EMAIL PROTECTED]> writes: > Let me make the point that signed overflow has been undefined since > before the C standard was finialized and in fact there is a nice > paper/book called "C Traps and Pitfalls[2]" which mentions all of this > back in 1988. C Traps and Pitfalls, like K&

Re: Autoconf manual's coverage of signed integer overflow & portability

Richard Kenner wrote: A few comments: Many portable C programs assume that signed integer overflow wraps around reliably using two's complement arithmetic. I'd replace "portable C programs" with "widely-used C programs". The normal use of "portable" means that it conforms to the standard.

Re: Autoconf manual's coverage of signed integer overflow & portability

> >> Many portable C programs assume that signed integer overflow wraps around > >> reliably using two's complement arithmetic. > > > > I was looking for an adjective that mean the programs work on a wide > variety of platforms, and "portable" seems more appropriate than > "widely-used". Maybe jus

Re: Autoconf manual's coverage of signed integer overflow & portability

[EMAIL PROTECTED] (Richard Kenner) writes: > A few comments: Thanks for the quick review. >> Many portable C programs assume that signed integer overflow wraps around >> reliably using two's complement arithmetic. > > I'd replace "portable C programs" with "widely-used C programs". The normal >

Re: Autoconf manual's coverage of signed integer overflow & portability

> > Today I updated the Autoconf manual to contain the following > description of the current situation with signed integer overflow. > This section of the manual is intended to advise programmers what to > do about portable C programs in this area. > > I think some discussion along these lines a

Re: Autoconf manual's coverage of signed integer overflow & portability

A few comments: > Many portable C programs assume that signed integer overflow wraps around > reliably using two's complement arithmetic. I'd replace "portable C programs" with "widely-used C programs". The normal use of "portable" means that it conforms to the standard. > Conversely, in at lea

Autoconf manual's coverage of signed integer overflow & portability

Today I updated the Autoconf manual to contain the following description of the current situation with signed integer overflow. This section of the manual is intended to advise programmers what to do about portable C programs in this area. I think some discussion along these lines also belongs in