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Re: How to get mantissa of long double?

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.lang.c++
Subject Re: How to get mantissa of long double?
Date 2021-10-04 09:52 +0200
Organization A noiseless patient Spider
Message-ID <sjebr5$ut3$1@dont-email.me> (permalink)
References (3 earlier) <sj7g9f$hsk$1@dont-email.me> <sj7hv5$v3u$1@dont-email.me> <sjbhfj$fd7$1@dont-email.me> <sjbvs8$9d9$1@dont-email.me> <sjc03i$a01$1@dont-email.me>

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On 03/10/2021 12:19, Bonita Montero wrote:
> Am 03.10.2021 um 12:15 schrieb Bart:
> 
>> Jesus. And I think this still doesn't do an actual long double!
> 
> long double isn't supported by many compilers for x86-64.
> long double should be avoided when possible because loads
> and stores are slow with long double.
> 

"long double" is supported by any C++ or C compiler, for any target,
that tries to come close to any current standards compliance.

What you probably mean is that on some targets, "long double" is the
same size as "double".  That's true for most 32-bit (and smaller)
targets.  Most 64-bit targets support larger "long double".

As happens so often, there is /one/ major exception to the common
practices used by (AFAICS) every other OS, every other processor, every
other compiler manufacturer - on Windows, and with MSVC, "long double"
is 64-bit.

"long double" should not be used where "double" will do, because it can
be a great deal slower on many platforms (the load and saves are
irrelevant).  You also have to question whether "long double" does what
you want, on any given target.  On smaller targets (or more limited
compilers, like MSVC), it gives you no benefits in accuracy or range
compared to "double".  On some, such as x86-64 with decent tools, it
generally gives you 80-bit types.  On others - almost any other 64-bit
system - it gives you 128-bit quad double, but it is likely to be
implemented in software rather than hardware.

However, it /is/ a valid type on all (reasonable) C and C++ systems, and
it is a perfectly reasonable question to ask how to handle it.  Some
aspects can be handled in a portable manner, others require
implementation-dependent details.

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Thread

How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-01 08:37 -0700
  Re: How to get mantissa of long double? RadicalRabbit@theburrow.co.uk - 2021-10-01 16:09 +0000
    Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-01 14:05 -0400
      Re: How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-01 17:23 -0700
        Re: How to get mantissa of long double? Manfred <noname@add.invalid> - 2021-10-02 18:58 +0200
          Re: How to get mantissa of long double? Manfred <noname@add.invalid> - 2021-10-02 19:21 +0200
  Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:18 +0200
    Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:20 +0200
      Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:25 +0200
        Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 19:53 +0200
          Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-03 08:09 +0200
            Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-03 11:15 +0100
              Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-03 12:19 +0200
                Re: How to get mantissa of long double? red floyd <no.spam@its.invalid> - 2021-10-03 18:03 -0700
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-04 09:52 +0200
                Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-04 09:59 +0000
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-04 13:50 +0200
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-04 20:04 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 07:12 +0200
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 09:47 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 16:46 +0200
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 19:04 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 19:13 +0200
                Re: How to get mantissa of long double? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-05 09:04 -0700
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 19:14 +0200
                Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-05 19:21 +0100
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 07:58 +0200
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-06 08:11 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 10:25 +0200
                Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-06 14:25 +0000
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 16:53 +0200
                Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-06 12:12 +0100
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 14:48 +0200
                Re: How to get mantissa of long double? red floyd <no.spam.here@its.invalid> - 2021-10-06 09:44 -0700
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 18:52 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-06 19:02 +0200
                Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-07 05:35 +0000
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-07 08:20 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-07 08:38 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-07 08:42 +0200
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-07 10:23 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-08 20:23 +0200
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-09 10:23 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-09 10:50 +0200
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-09 09:02 +0000
                Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-09 14:57 +0000
                Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-09 12:16 +0100
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-09 15:10 +0200
                Re: How to get mantissa of long double? red floyd <no.spam.here@its.invalid> - 2021-10-09 10:26 -0700
                Re: How to get mantissa of long double? Vir Campestris <vir.campestris@invalid.invalid> - 2021-10-12 21:23 +0100
                Re: How to get mantissa of long double? RadicalRabbit@theburrow.co.uk - 2021-10-13 10:30 +0000
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-07 08:38 +0200
                Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-08 04:37 +0000
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-08 07:54 +0200
                Re: How to get mantissa of long double? red floyd <no.spam.here@its.invalid> - 2021-10-07 22:44 -0700
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-07 08:17 +0200
                Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-08 04:39 +0000
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-08 09:25 +0200
                Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-08 14:34 +0000
                Re: How to get mantissa of long double? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-06 13:57 -0700
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-05 19:34 +0000
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-05 19:33 +0000
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-05 10:19 +0000
                Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-04 14:06 +0100
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-04 16:12 +0200
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 16:15 +0000
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 16:15 +0000
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 09:48 +0200
                Re: How to get mantissa of long double? Juha Nieminen <nospam@thanks.invalid> - 2021-10-05 05:19 +0000
                Re: How to get mantissa of long double? David Brown <david.brown@hesbynett.no> - 2021-10-05 10:00 +0200
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-05 16:47 +0200
                Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-04 14:37 +0000
                Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-04 16:53 +0200
                Re: How to get mantissa of long double? scott@slp53.sl.home (Scott Lurndal) - 2021-10-04 17:08 +0000
                Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-04 20:22 +0100
    Re: How to get mantissa of long double? Bart <bc@freeuk.com> - 2021-10-01 19:09 +0100
      Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-01 20:16 +0200
  Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-01 18:53 +0000
    Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-01 20:19 -0400
      Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 02:16 +0000
        Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 01:28 -0400
        Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 01:56 -0400
          Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-02 10:59 +0000
            Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 14:57 -0400
            Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 15:37 -0400
              Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 00:47 +0000
                Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-03 23:42 -0400
                Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 04:35 +0000
  Re: How to get mantissa of long double? Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-02 12:09 +0200
  Re: How to get mantissa of long double? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-10-02 21:00 +0200
    Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-02 15:12 -0400
      Re: How to get mantissa of long double? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-10-02 21:23 +0200
        Re: How to get mantissa of long double? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-10-02 21:27 +0200
          Re: How to get mantissa of long double? Manfred <noname@add.invalid> - 2021-10-02 23:19 +0200
        Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-03 23:43 -0400
      Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-03 00:45 +0000
        Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-03 23:31 -0400
          Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 04:34 +0000
            Re: How to get mantissa of long double? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-04 11:30 -0400
              Re: How to get mantissa of long double? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-04 16:19 +0000
    Re: How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-03 00:35 -0700
  Re: How to get mantissa of long double? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-10-03 15:02 +0100
    Re: How to get mantissa of long double? wij <wyniijj@gmail.com> - 2021-10-03 18:46 -0700

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