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Re: Detect Math Errors in Functions

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David Brown <david.brown@hesbynett.no> writes:

> 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.

FWIW, here's the exact language of C89.

--8<---------------cut here---------------start------------->8---
  A computation involving unsigned operands can never overflow, because
  a result that cannot be represented by the resulting unsigned integer
  type is reduced modulo the number that is one greater than the largest
  value that can be represented by the resulting unsigned integer type.
  -- C89, section 3.1.2.5
--8<---------------cut here---------------end--------------->8---

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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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