Re: Handling numeric types in interpreter

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Handling numeric types in interpreter
Date	2015-07-28 11:52 -0700
Organization	None to speak of
Message-ID	<ln4mkonmhm.fsf@kst-u.example.com> (permalink)
References	(3 earlier) <mourp8$mf$1@dont-email.me> <movvkj$leq$1@news.xmission.com> <91ee1672-182a-4968-8d22-610a21495452@googlegroups.com> <lnoaj0xj0b.fsf@kst-u.example.com> <mp8fe2$kn1$1@dont-email.me>

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ais523 <ais523@nethack4.org> writes:
> Keith Thompson wrote:
>> I have no problem with you conclusion (that double is good enough for
>> your purposes).  I disagree with your rationale (that long double is
>> potentially non-portable).
>
> long double is actually one of the least portable C89 features.
>
> The problem is that both the C standard, and comp.lang.c, tend to
> consider a C implementation to be a single, monolithic object. In
> practice, C implementations are normally provided as multiple parts: a
> linker, a compiler, a standard library, header files, perhaps others.
>
> If all the parts of an implementation cooperate with each other, then
> (by now) the result can nearly always be used as a conforming C89
> compiler (although often you'll have to use a command line option to
> request C89 conformance). However, it's not that uncommon to have
> situations where some of the parts are mismatched; perhaps the library
> you're using was designed for a different compiler than the compiler
> you're using. This sort of mismatch, unsurprisingly, is capable of
> introducing problems that cause the combined implementation to fall
> short of C89.
>
> One of the most common mismatched combinations seen in practice occurs
> on Windows, with mingw (compiler + linker + headers) + msvcrt (library);
> this combination is commonly used as a result of licensing issues.
> msvcrt is not designed for use with mingw, and in particular, the two
> components disagree on the value of sizeof(long double). The upshot is
> that when using this combination, arguments of long double type cannot
> be used reliably in standard library calls (most commonly seen in the
> case of printf, for which the header files cannot work around the
> problem because printf is variadic).

MinGW is the only implementation I've heard of that has this problem
with long double (which doesn't imply that there aren't others).
And as it happens there's an easy workaround: define the macro
__USE_MINGW_ANSI_STDIO as 1, which you can do by compiling with

    gcc -D__USE_MINGW_ANSI_STDIO=1

If I recall correctly, Microsoft's compiler and runtime library give
double and long double the same size and representation (which is
perfectly legal, though it does miss out on the opportunity to use
floating-point with a greater range and precision), whereas gcc
makes long double bigger than double.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

Handling numeric types in interpreter luser droog <luser.droog@gmail.com> - 2015-07-13 19:33 -0700
  Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-14 07:31 +0200
  Handling numeric types in interpreter asetofsymbols@gmail.com - 2015-07-14 00:35 -0700
  Re: Handling numeric types in interpreter David Kleinecke <dkleinecke@gmail.com> - 2015-07-14 08:55 -0700
  Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-15 23:18 +0100
    Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 00:21 -0700
      Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-24 08:36 -0700
        Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 11:04 -0700
          Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-24 12:25 -0700
            Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-24 22:21 -0400
              Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 02:28 -0700
                Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-25 15:16 +0100
                Re: Handling numeric types in interpreter Richard Damon <Richard@Damon-Family.org> - 2015-07-25 11:03 -0400
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 10:05 -0700
              Re: Handling numeric types in interpreter gazelle@shell.xmission.com (Kenny McCormack) - 2015-07-25 12:32 +0000
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 06:12 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 10:08 -0700
                Re: Handling numeric types in interpreter ais523 <ais523@nethack4.org> - 2015-07-28 17:50 +0000
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-28 11:52 -0700
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-28 12:25 -0700
                Re: Handling numeric types in interpreter Richard Heathfield <rjh@cpax.org.uk> - 2015-07-28 20:52 +0100
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-28 23:01 +0200
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-28 14:44 -0700
                Re: Handling numeric types in interpreter Ian Collins <ian-news@hotmail.com> - 2015-07-29 09:43 +1200
                Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-28 23:10 +0000
                Re: Handling numeric types in interpreter Ian Collins <ian-news@hotmail.com> - 2015-07-29 12:04 +1200
                Re: Handling numeric types in interpreter Melzzzzz <mel@zzzzz.com> - 2015-07-29 02:39 +0200
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 12:04 +0200
                Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-29 14:58 +0000
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 14:14 +0200
                Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-29 13:29 +0100
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 08:48 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 08:45 -0700
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-28 16:28 -0700
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 12:02 +0200
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 08:51 -0700
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 18:35 +0200
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 10:47 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-25 15:46 -0500
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 14:08 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 15:42 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 00:31 -0500
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-25 17:48 -0400
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-25 17:31 -0500
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 15:57 -0700
                Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-26 01:07 +0100
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 17:26 -0700
                Re: Handling numeric types in interpreter Richard Damon <Richard@Damon-Family.org> - 2015-07-25 22:25 -0400
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-25 19:04 -0400
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 00:23 -0500
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-26 08:24 -0400
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-26 06:36 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 16:30 -0500
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-26 15:42 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 16:28 -0500
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-26 18:57 -0400
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-26 16:20 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 15:58 -0700
              Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-25 12:56 -0400
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 14:18 -0700
      Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-24 18:06 +0000
        Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 11:16 -0700
          Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-24 23:06 +0000
            Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 16:21 -0700
  Re: Handling numeric types in interpreter Michael Angelo Ravera <maravera@prodigy.net> - 2015-07-15 19:13 -0700
    Re: Handling numeric types in interpreter luser droog <luser.droog@gmail.com> - 2015-07-23 08:36 -0700

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