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Re: Decimal Floating Point

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On 2021-09-11, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
> Kaz Kylheku <563-365-8930@kylheku.com> writes:
>> On 2021-09-10, Stefan Ram <ram@zedat.fu-berlin.de> wrote:
>>> Fabian Russell <fr314159@gmail.com> writes:
>>>>Why bother to include the new types yet now allow them to be used
>>>>arithmetically like all other standard numeric types?
>>>
>>>   One would have to define many new rules for cases like
>>>   "double + decimal" and so on. And these would have to be
>>
>> This cn be handled via, say, a general decimal contagion rule.
>> The double operand is converted to the best approximation in decimal
>> floating point, or undefined behavior if it is out of range.  Then the
>> calculation proceeds as decimal <op> decimal.
>
> As I mentioned yesterday, the latest C23 draft includes (optional)
> decimal FP.  It simply disallows mixing decimal and standard
> floating-point types as operands.  N2596 6.3.1.8.
>
> It strikes me as a reasonable decision to require the programmer
> to decide (by using a cast) whether to perform the operation in
> standard or decimal floating-point.

It strikes me as prudent: it's the best way to delay making a decision
which can later be amended in a backward-compatible way.

If it turns out that promoting from decimal to double is preferred, then
that can just be blessed as not requiring a diagnostic.  Compilers which
previously diagnosed it turn that into a warning and move on. Existing
code is unaffected.

It's reasonable from a safety POV also, but it's not in the "C spirit".
C is not Ada.

The C programmer expects implicit conversions.  Denying them between two
flavors of floating-point won't save the language due to all the
existing ones. It's not a "good start" to anything that leads anywhere.

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

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Decimal Floating Point Fabian Russell <fr314159@gmail.com> - 2021-09-10 06:35 -0700
  Re: Decimal Floating Point "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-09-10 08:17 -0700
    Re: Decimal Floating Point scott@slp53.sl.home (Scott Lurndal) - 2021-09-10 15:44 +0000
      Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-10 12:06 -0400
        Re: Decimal Floating Point Manfred <noname@add.invalid> - 2021-09-10 18:09 +0200
          Re: Decimal Floating Point Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-09-10 16:23 +0000
          Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-10 12:37 -0400
        Re: Decimal Floating Point Fabian Russell <fr314159@gmail.com> - 2021-09-10 09:38 -0700
          Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-10 12:58 -0400
        Re: Decimal Floating Point Eli the Bearded <*@eli.users.panix.com> - 2021-09-10 18:11 +0000
          Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-10 12:13 -0700
            Re: Decimal Floating Point Fabian Russell <fr314159@gmail.com> - 2021-09-10 14:52 -0700
            Re: Decimal Floating Point Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-09-11 07:09 -0700
          Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-10 23:23 -0400
        Re: Decimal Floating Point scott@slp53.sl.home (Scott Lurndal) - 2021-09-10 19:04 +0000
          Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-10 23:23 -0400
            Re: Decimal Floating Point Manfred <noname@add.invalid> - 2021-09-18 19:20 +0200
              Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-20 00:16 -0400
    Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-10 11:14 -0700
      Re: Decimal Floating Point Bart <bc@freeuk.com> - 2021-09-10 23:50 +0100
        Re: Decimal Floating Point David Brown <david.brown@hesbynett.no> - 2021-09-11 20:22 +0200
          Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-11 15:37 -0700
            Re: Decimal Floating Point David Brown <david.brown@hesbynett.no> - 2021-09-12 12:58 +0200
      Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-10 17:36 -0700
  Re: Decimal Floating Point Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-10 18:04 +0200
  Re: Decimal Floating Point Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-10 18:06 +0200
    Re: Decimal Floating Point Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-09-10 09:37 -0700
      Re: Decimal Floating Point Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-10 20:43 +0200
    Re: Decimal Floating Point "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-09-10 09:52 -0700
      Re: Decimal Floating Point Fabian Russell <fr314159@gmail.com> - 2021-09-10 10:08 -0700
        Re: Decimal Floating Point antispam@math.uni.wroc.pl - 2021-09-11 00:36 +0000
    Re: Decimal Floating Point scott@slp53.sl.home (Scott Lurndal) - 2021-09-10 19:07 +0000
      Re: Decimal Floating Point Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 06:31 +0200
        Re: Decimal Floating Point Siri Cruise <chine.bleu@yahoo.com> - 2021-09-10 23:29 -0700
          Re: Decimal Floating Point Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 16:31 +0200
            Re: Decimal Floating Point Barry Schwarz <schwarzb@delq.com> - 2021-09-11 10:04 -0700
            Re: Decimal Floating Point James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-11 15:08 -0400
              Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-11 15:39 -0700
                Re: Decimal Floating Point Richard Damon <Richard@Damon-Family.org> - 2021-09-11 19:28 -0400
  Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-10 11:21 -0700
  Re: Decimal Floating Point Philipp Klaus Krause <pkk@spth.de> - 2021-09-10 23:29 +0200
  Re: Decimal Floating Point Kaz Kylheku <563-365-8930@kylheku.com> - 2021-09-11 16:59 +0000
    Re: Decimal Floating Point Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-11 16:05 -0700
      Re: Decimal Floating Point Kaz Kylheku <563-365-8930@kylheku.com> - 2021-09-14 16:25 +0000
  Re: Decimal Floating Point "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-09-12 13:08 -0700
  Re: Decimal Floating Point Thomas David Rivers <rivers@dignus.com> - 2021-09-13 22:23 -0400

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