Re: What happened to short float?

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c, comp.std.c
Subject	Re: What happened to short float?
Date	2018-02-07 16:59 -0800
Organization	None to speak of
Message-ID	<lnk1voz46u.fsf@kst-u.example.com> (permalink)
References	<p3nt6t$uid$1@solani.org> <ef0ada5f-6cbd-a060-fab8-894272f9b914@verizon.net> <p52ngk$evf$1@dont-email.me> <fdr6e4Fp1fcU1@mid.individual.net> <20180208012936.09fa549ce0fe0785da7cf560@gmail.com>

Cross-posted to 2 groups.

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GOTHIER Nathan <nathan.gothier@gmail.com> writes:
> On Mon, 5 Feb 2018 08:55:00 -0500
> Tim Prince <tprince@intelretiree.com> wrote:
>> On 2/2/2018 5:08 PM, jacobnavia wrote:
>> Perhaps there is little more to say.  The format has little attraction
>> for portable code, as many platforms can't implement it efficiently.
>
> Any IEEE 754 compliant hardware that supports the float type (aka single
> precision float) would be able to support the short float type (i.e.
> less or equal to single precision float).

Wouldn't you need extra code to convert between 16-bit and 32-bit
formats?  For normal values you'd need to do some bit-twiddling.
Special values like infinities, NaNs, subnormals, and so forth might
require some extra work (I haven't looked into the details).

> Actually the AMD64 architecture FPU only computes 80-bit floats and
> the long double type is a synonym for the double or float types since
> they are internally the same thing.
>
> The short float type implementation shouldn't be as hard as:
>
> typedef float sflt_t;
>
> Once more, the F16C instruction set enables to convert single precision
> floats to half precision floats for storage purpose. Thus, the
> implementation shouldn't be as hard as:
>
> typedef char half_t[2];

(I'd use uint16_t, or at least unsigned char[2] rather than char[2].)

> typedef half_t sflt_t;

Sure, if you have a CPU instruction that does the conversion, it's easy.

If you don't, it's not prohitively difficult, but it's not quite as
obvious that it's worth the effort.

-- 
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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Re: What happened to short float? jacobnavia <jacob@jacob.remcomp.fr> - 2018-02-02 23:08 +0100
  Re: What happened to short float? Jakob Bohm <jb-usenet@wisemo.com> - 2018-02-05 07:57 +0100
    Re: What happened to short float? jameskuyper@verizon.net - 2018-02-05 05:31 -0800
  Re: What happened to short float? Tim Prince <tprince@intelretiree.com> - 2018-02-05 08:55 -0500
    Re: What happened to short float? jacobnavia <jacob@jacob.remcomp.fr> - 2018-02-05 15:46 +0100
    Re: What happened to short float? GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-08 01:29 +0100
      Re: What happened to short float? Keith Thompson <kst-u@mib.org> - 2018-02-07 16:59 -0800
        Re: What happened to short float? Philipp Klaus Krause <pkk@spth.de> - 2018-02-08 09:08 +0100
          Re: What happened to short float? Keith Thompson <kst-u@mib.org> - 2018-02-08 09:27 -0800
        Re: What happened to short float? GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-08 09:54 +0100
          Re: What happened to short float? Keith Thompson <kst-u@mib.org> - 2018-02-08 10:13 -0800
        Re: What happened to short float? jameskuyper@verizon.net - 2018-02-08 06:36 -0800
          Re: What happened to short float? GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-08 17:04 +0100
            Re: What happened to short float? jameskuyper@verizon.net - 2018-02-08 08:56 -0800
              Re: What happened to short float? scott@slp53.sl.home (Scott Lurndal) - 2018-02-08 17:23 +0000
              Re: What happened to short float? GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-08 18:52 +0100
                Re: What happened to short float? jameskuyper@verizon.net - 2018-02-08 11:27 -0800
                Re: What happened to short float? GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-08 22:58 +0100
          Re: What happened to short float? Keith Thompson <kst-u@mib.org> - 2018-02-08 10:18 -0800
      Re: What happened to short float? Jakob Bohm <jb-usenet@wisemo.com> - 2018-02-08 18:59 +0100
        Re: What happened to short float? Robert Wessel <robertwessel2@yahoo.com> - 2018-02-08 16:22 -0600
          Re: What happened to short float? Jakob Bohm <jb-usenet@wisemo.com> - 2018-02-09 15:01 +0100

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