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Re: Detect Math Errors in Functions

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On 08/09/2021 12:20, Juha Nieminen wrote:
> red floyd <no.spam.here@its.invalid> wrote:
>> I don't think so.  I believe unsigned rollover is defined.  If x was a
>> regular long, that's another matter.
> 
> Indeed. Unsigned integers use 2's complement arithmetic as per the standard.
> (Well, pratically speaking 2's complement.)
> 

I think I know what you are trying to say, but it is a strange way to
say it.  "Two's complement" only makes sense for signed integers - it
has no meaning for unsigned types.

Unsigned types in C and C++ are defined as modulo types.
Conventionally, we may say they "wrap on overflow" - but to be more
accurate, there is no overflow.  The result of adding unsigned ints "a"
and "b" is the value of "(a + b) % 2^n" using standard mathematical
arithmetic, where "n" is the number of value bits in unsigned int.


> It's only with signed integers that overflow and underflow are undefined.

Yes.

> (And for a reason, as there are architectures where this may cause a fault
> signal to be thrown.)
> 

That is perhaps one of several reasons, but it is not the only one.  The
primary reason, as I see it, is that overflow of signed integer
arithmetic will give you the wrong answer.  Picking a definition for the
result does not make it correct or useful - it merely hinders tools in
helping you to find the errors in your code.

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Thread

Detect Math Errors in Functions Joseph Hesse <joeh@gmail.com> - 2021-09-01 07:31 +0200
  Re: Detect Math Errors in Functions Barry Schwarz <schwarzb@delq.com> - 2021-08-31 23:54 -0700
    Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-01 09:30 +0200
      Re: Detect Math Errors in Functions Barry Schwarz <schwarzb@delq.com> - 2021-09-01 07:53 -0700
        Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-01 17:50 +0200
        Re: Detect Math Errors in Functions James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-01 12:28 -0400
        Re: Detect Math Errors in Functions Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2021-09-01 17:38 +0100
    Re: Detect Math Errors in Functions David Brown <david.brown@hesbynett.no> - 2021-09-01 09:50 +0200
      Re: Detect Math Errors in Functions Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2021-09-01 16:38 +0100
        Re: Detect Math Errors in Functions David Brown <david.brown@hesbynett.no> - 2021-09-01 19:25 +0200
          Re: Detect Math Errors in Functions Hope Rouselle <hrouselle@jevedi.com> - 2021-09-06 11:04 -0300
      Re: Detect Math Errors in Functions Cholo Lennon <chololennon@hotmail.com> - 2021-09-06 00:20 -0300
        Re: Detect Math Errors in Functions "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-06 07:23 +0200
          Re: Detect Math Errors in Functions Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2021-09-06 20:34 -0400
  Re: Detect Math Errors in Functions Juha Nieminen <nospam@thanks.invalid> - 2021-09-01 18:22 +0000
  Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-01 21:02 +0200
    Re: Detect Math Errors in Functions David Brown <david.brown@hesbynett.no> - 2021-09-02 11:53 +0200
  Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-01 21:10 +0200
    Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-02 05:31 +0200
      Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-02 07:51 +0200
    Re: Detect Math Errors in Functions Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2021-09-06 20:47 -0400
      Re: Detect Math Errors in Functions red floyd <no.spam.here@its.invalid> - 2021-09-06 20:24 -0700
        Re: Detect Math Errors in Functions Juha Nieminen <nospam@thanks.invalid> - 2021-09-08 10:20 +0000
          Re: Detect Math Errors in Functions David Brown <david.brown@hesbynett.no> - 2021-09-08 13:17 +0200
            Re: Detect Math Errors in Functions Hope Rouselle <hrouselle@jevedi.com> - 2021-09-08 10:24 -0300
      Re: Detect Math Errors in Functions Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-07 09:10 +0200

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