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Groups > comp.lang.c > #66508

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 14:44 -0700
Organization None to speak of
Message-ID <lnzj2glzxm.fsf@kst-u.example.com> (permalink)
References (5 earlier) <91ee1672-182a-4968-8d22-610a21495452@googlegroups.com> <lnoaj0xj0b.fsf@kst-u.example.com> <mp8fe2$kn1$1@dont-email.me> <mp8mes$hqh$1@dont-email.me> <mp8qh3$3g5$1@dont-email.me>

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jacobnavia <jacob@jacob.remcomp.fr> writes:
> Le 28/07/2015 21:52, Richard Heathfield a écrit :
>> On 28/07/15 18:50, ais523 wrote:
>>> 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.
>>
>> In a sense, it is one of the /most/ portable features! The Standard
>> doesn't require it to do anything that double doesn't do, and therefore
>> any implementation can implement it for free by interpreting it as a
>> synonym for double. (And some do.) People who have to write portable
>> code know this, so they don't bother using it, making it 100% portable
>> and 100% useless.
>
> I disagree.
>
> lcc-win has two implementations of long double: the "standard" intel 80 
> bits long double in hardware (FPU) and a software implementation of 128 
> bit long doubles (called float128_t)
[...]
> For people that do not do numerical work long double is useless. OK.
>
> But for other people long double is a necessity.

I disagree with both of you.

For portable code you can't assume that long double is bigger than
double -- but you can assume that it's at least as big.  If you
want to use the biggest floating-point type available, that's
long double.  On some platforms you won't get any more precision
or range than double; on others, you will.  If the extra range and
precision on *some* systems is worth the inconsistency then you win.
(double isn't guaranteed to have the same range and precision across
systems, but these days it's *usually* 64-bit IEEE.)

Also, since long double is guaranteed to be the largest
floating-point type (excluding extensions), it can be handy if
client code might be giving you values of any floating-point type.

On the other hand, if "long double is a necessity" (by which I
presume you mean that range and/or precision greater than that of
double is a necessity), then you're out of luck if you're using a
system where double and long double have the same representation.
Using a different compiler that has a larger long double type is
great if you have that option.  Not everyone does.

BTW, I'm curious about your two different implementations of long
double, 80 and 128 bits.  How do you specify which one you want
to use?  If it's a compile-time option, does the linker prevent
you from linking object files that don't use the same representation?

-- 
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"

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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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