Re: Adjusting printf() rounding

From	Andrey Tarasevich <andreytarasevich@hotmail.com>
Newsgroups	comp.lang.c++
Subject	Re: Adjusting printf() rounding
Date	2022-04-09 09:10 -0700
Organization	A noiseless patient Spider
Message-ID	<t2sb6d$as9$1@dont-email.me> (permalink)
References	<t2pag0$eab$1@dont-email.me> <t2sarf$7g9$1@dont-email.me>

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On 4/9/2022 9:05 AM, Andrey Tarasevich wrote:
> On 4/8/2022 5:40 AM, Paavo Helde wrote:
>>
>> What's worse, it appears MSVC have not kept the promises which they 
>> made, and have reverted back to pre-MSVC19 behavior in VS2019 Update 
>> 11 (_MSC_VER==1929), rounding ties now up again.
>>
> 
> Technically, it is no longer a promise of MSVC, but rather a promise of 
> Windows SDK. However, it is run-time controllable through such internal 
> SDK options as
> 
>    _CRT_INTERNAL_PRINTF_STANDARD_ROUNDING
> 
> and apparently different versions of MSVC set different initial settings 
> in the program's startup code, since the same version of SDK produces 
> different results in different versions of MSVC.
> 

Also, once you enable

   _CRT_INTERNAL_PRINTF_STANDARD_ROUNDING

`printf` in MSVC begins to obey the rounding modes set by `fesetround`

   #include <cstdio>
   #include <cfenv>

   int main()
   {
     *__local_stdio_printf_options() |=
       _CRT_INTERNAL_PRINTF_STANDARD_ROUNDING;

     std::printf("%.3g\n", 212.5);

     std::fesetround(FE_UPWARD);
     std::printf("%.3g\n", 212.5);

     std::fesetround(FE_DOWNWARD);
     std::printf("%.3g\n", 212.5);

     std::fesetround(FE_TONEAREST);
     std::printf("%.3g\n", 212.5);
   }

   212
   213
   212
   212

-- 
Best regards,
Andrey Tarasevich

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Thread

Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-08 15:40 +0300
  Re: Adjusting printf() rounding Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-08 06:02 -0700
  Re: Adjusting printf() rounding Marcel Mueller <news.5.maazl@spamgourmet.org> - 2022-04-08 18:21 +0200
    Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-08 19:38 +0300
      Re: Adjusting printf() rounding Sams Lara <samlara622@gmail.com> - 2022-04-08 18:48 +0100
        Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-08 23:44 +0300
          Re: Adjusting printf() rounding Marcel Mueller <news.5.maazl@spamgourmet.org> - 2022-04-09 12:58 +0200
            Re: Adjusting printf() rounding Geoff <geoff@invalid.invalid> - 2022-04-09 08:45 -0700
            Re: Adjusting printf() rounding Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-09 13:05 -0700
              Re: Adjusting printf() rounding red floyd <no.spam.here@its.invalid> - 2022-04-09 13:36 -0700
            Re: Adjusting printf() rounding Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 16:08 -0700
  Re: Adjusting printf() rounding Manfred <noname@add.invalid> - 2022-04-08 21:30 +0200
  Re: Adjusting printf() rounding "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-04-09 10:11 +0200
    Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-10 16:39 +0300
      Re: Adjusting printf() rounding Sams Lara <samlara622@gmail.com> - 2022-04-10 18:36 +0100
        Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-10 21:50 +0300
  Re: Adjusting printf() rounding Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 09:05 -0700
    Re: Adjusting printf() rounding Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 09:10 -0700

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