Re: does a double cast to unsigned makes sense in any circumstance?

From	Manfred <noname@add.invalid>
Newsgroups	comp.lang.c
Subject	Re: does a double cast to unsigned makes sense in any circumstance?
Date	2022-01-30 03:45 +0100
Organization	Aioe.org NNTP Server
Message-ID	<st4u3j$st8$1@gioia.aioe.org> (permalink)
References	(4 earlier) <87y23fxt9p.fsf@nosuchdomain.example.com> <86a6fur0rh.fsf@levado.to> <87tue2xbu5.fsf@nosuchdomain.example.com> <864k5n9wdw.fsf@levado.to> <87fsp7ky9m.fsf@nosuchdomain.example.com>

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On 1/29/2022 4:37 AM, Keith Thompson wrote:
> Meredith Montgomery <mmontgomery@levado.to> writes:
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>> Meredith Montgomery <mmontgomery@levado.to> writes:
>>>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>>>> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>>>>> [...]
>>>>>> "... the value is converted by repeatedly adding ... one more than the
>>>>>> maximum value that can be represented in the new type until the value is
>>>>>> in the range of the new type." (6.3.1.3p2).
>>>>>>
>>>>>> It's the other direction that's dangerous: conversion of an integer
>>>>>> value to a signed integer type that is not representable in that type
>>>>>> has undefined behavior.
>>>>>
>>>>> No, converting an out-of-range integer value to a signed integer type
>>>>> yields an implementation-defined result or raises an
>>>>> implementation-defined signal.  (C99 added the option of raising a
>>>>> signal; in my opinion that was a bad idea.)
>>>>
>>>> Just curious --- why do you think a signal is a bad idea?
>>>
>>> A signal isn't inherently a bad idea, particularly if portable code can
>>> handle it.  But the fact that the signal is implementation-defined makes
>>> that impossible.  (And freestanding implementations needn't support
>>> <signal.h>.)
>>
>> What's a freestanding implementation?
> 
> See section 4 of any edition of the C standard.  I usually use
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf, a draft
> that's close to C11.
> 
>      The two forms of *conforming implementation* are hosted and
>      freestanding. A *conforming hosted implementation* shall accept any
>      strictly conforming program. A *conforming freestanding implementation*
>      shall accept any strictly conforming program in which the use of the
>      features specified in the library clause (clause 7) is confined to the
>      contents of the standard headers <float.h>, <iso646.h>, <limits.h>,
>      <stdalign.h>, <stdarg.h>, <stdbool.h>, <stddef.h>, <stdint.h>, and
>      <stdnoreturn.h>. A conforming implementation may have extensions
>      (including additional library functions), provided they do not alter
>      the behavior of any strictly conforming program.
> 
> Basically a hosted implementation is the kind that you're most likely to
> encounter.  It generates code that runs under an operating system, and
> it supports the entire standard library.  A freestanding implementation
> targets an embedded system that might not have an operating system at
> all.  The only standard library headers that must be supported are the
> ones that don't declare any functions.  A freestanding implementation
> might provide some library functions, but it isn't required to.
> 

A freestanding implementation might also target the OS itself of a 
common system (not necessarily embedded), right?

Thread

does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-03 14:15 -0300
  Re: does a double cast to unsigned makes sense in any circumstance? Bart <bc@freeuk.com> - 2022-01-03 17:32 +0000
    Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-15 22:09 -0300
  Re: does a double cast to unsigned makes sense in any circumstance? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-01-03 10:06 -0800
    Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-15 22:12 -0300
      Re: does a double cast to unsigned makes sense in any circumstance? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-15 23:12 -0500
        Re: does a double cast to unsigned makes sense in any circumstance? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-20 19:37 -0800
          Re: does a double cast to unsigned makes sense in any circumstance? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-01-21 09:35 -0800
            Re: does a double cast to unsigned makes sense in any circumstance? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-21 17:19 -0800
  Re: does a double cast to unsigned makes sense in any circumstance? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-03 19:31 +0100
    Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-15 22:14 -0300
      Re: does a double cast to unsigned makes sense in any circumstance? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-15 23:24 -0500
        Re: does a double cast to unsigned makes sense in any circumstance? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-16 13:30 -0800
          Re: does a double cast to unsigned makes sense in any circumstance? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-16 23:25 -0500
          Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 09:43 -0300
            Re: does a double cast to unsigned makes sense in any circumstance? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-17 13:59 -0800
              Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-28 22:13 -0300
                Re: does a double cast to unsigned makes sense in any circumstance? James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-28 21:29 -0500
                Re: does a double cast to unsigned makes sense in any circumstance? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-02-03 22:28 -0800
                Re: does a double cast to unsigned makes sense in any circumstance? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-02-04 10:43 -0800
                Re: does a double cast to unsigned makes sense in any circumstance? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-28 19:37 -0800
                Re: does a double cast to unsigned makes sense in any circumstance? Manfred <noname@add.invalid> - 2022-01-30 03:45 +0100
                Re: does a double cast to unsigned makes sense in any circumstance? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-30 00:01 -0800
                Re: does a double cast to unsigned makes sense in any circumstance? Richard Damon <Richard@Damon-Family.org> - 2022-01-30 12:59 -0500
        Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 09:41 -0300
  Re: does a double cast to unsigned makes sense in any circumstance? Richard Damon <Richard@Damon-Family.org> - 2022-01-03 14:37 -0500
    Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-15 22:15 -0300
      Re: does a double cast to unsigned makes sense in any circumstance? Richard Damon <Richard@Damon-Family.org> - 2022-01-15 20:55 -0500
        Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 09:44 -0300
    Re: does a double cast to unsigned makes sense in any circumstance? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-16 05:13 +0100
  Re: does a double cast to unsigned makes sense in any circumstance? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-15 18:53 -0800
    Re: does a double cast to unsigned makes sense in any circumstance? Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 09:46 -0300
    Re: does a double cast to unsigned makes sense in any circumstance? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-29 16:57 +0100
      Re: does a double cast to unsigned makes sense in any circumstance? Öö Tiib <ootiib@hot.ee> - 2022-01-29 09:54 -0800
        Re: does a double cast to unsigned makes sense in any circumstance? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-30 13:17 +0100
          Re: does a double cast to unsigned makes sense in any circumstance? Öö Tiib <ootiib@hot.ee> - 2022-01-30 23:53 -0800

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