Re: Float Vs Double

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: Float Vs Double
Date	2016-08-23 15:07 +0200
Organization	A noiseless patient Spider
Message-ID	<nphhqp$db1$1@dont-email.me> (permalink)
References	(15 earlier) <npg1jd$b3k$2@jstuckle.eternal-september.org> <874m6ctktg.fsf@bsb.me.uk> <npgak4$13a$1@jstuckle.eternal-september.org> <npgui2$hjt$1@dont-email.me> <nphepg$1dn$3@jstuckle.eternal-september.org>

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On 23/08/16 14:15, Jerry Stuckle wrote:
> On 8/23/2016 3:38 AM, David Brown wrote:
>> On 23/08/16 03:58, Jerry Stuckle wrote:
>>> On 8/22/2016 8:01 PM, Ben Bacarisse wrote:
>>>> Jerry Stuckle <jstucklex@attglobal.net> writes:
>>>>
>>>>> On 8/22/2016 11:39 AM, supercat@casperkitty.com wrote:
>>>>>> On Sunday, August 21, 2016 at 5:31:13 PM UTC-5, Jerry Stuckle wrote:
>>>>>>> For instance - I've seen it implemented as storing the digits in a
>>>>>>> string.  Quite easy to implement - but performance was terrible, as you
>>>>>>> can imagine.  OTOH, I implemented one back in the 80's based on two
>>>>>>> digits per byte, using 808x assembler.  Much faster, but not portable
>>>>>>> and not all that easy.
>>>>>>
>>>>>> I'm surprised I haven't seen more "decimal math" libraries using 9 digits
>>>>>> per word; such a thing would seem like a natural fit on a 32-bit processor
>>>>>> with a 32x32->64 multiply.  Performance would be likely slower than for
>>>>>> binary math, but nowhere near as slow as using single-digit or two-digit
>>>>>> chunks (on processors which can't use a carry flag for extended-precision
>>>>>> math, addition and subtraction could benefit from the fact that the sum
>>>>>> or difference of any two 9-digit chunks could fit in a 32-bit signed "int").
>>>>>>
>>>>>
>>>>> 9 digits per word would not be decimal math.  The most you could get
>>>>> into 32 bits would be 8 decimal digits.
>>>>
>>>> I think what supercat is talking about might otherwise be called base
>>>> 1,000,000,000 arithmetic.
>>>>
>>>>> And I suspect trying it would
>>>>> be even slower than decimal math.  It would be much more complicated to
>>>>> implement.
>>>>
>>>> In software, it's faster and simpler than using BCD-type schemes, but
>>>> it's a matter of definition if is a decimal scheme or not.
>>>>
>>>
>>> I understand what he's after, and my comments stand.  For instance, how
>>> easy would it be to subtract 123.456 from 789012.345678?  Not that hard
>>> with BCD, but very difficult with supercat's idea.  Adjusting for the
>>> decimal point would not be easy.
>>>
>>
>> That would depend on whether he is considering just integers (in which
>> case arithmetic with a decimal point is /really/ hard!), or a
>> representation supporting multiple 9-digit chunks (in which case,
>> subtracting 000000123.456000000 from 000789012.345678000 would be quite
>> simple), or something with a floating decimal point (which would be very
>> messy).
>>
>> Personally, I don't think there would be anything much to be gained from
>> base 1G formats, except perhaps in very niche cases.
>>
>>
>>
> 
> The whole thread is about real numbers, not integers, David.  And seldom
> do the numbers always have the same number of decimal places.
> 

Just because the thread is about real numbers, does not mean that
Supercat is still talking about them!

But I think that in many situations where you might be interested in
tracking your numbers in decimal digit formats rather than floating
point, scaled integer, or other binary formats, then you probably /do/
have a fixed number of decimal digits.  Financial calculations would be
an example.

The exception would be in mathematical calculations where you want
arbitrary precision in your decimal calculations.

And in either case, I can't see why storing 9 digits in 32-bit chunks is
going to be much more complicated than storing 1 or 2 digits in 8-bit
chunks (BCD, packed or unpacked).  It will certainly be more efficient
for calculations.  18 digits in 64-bit chunks is going to be even better
on modern cpus.

Thread

Float Vs Double Real Troll <real.troll@trolls.com> - 2016-08-07 17:59 -0400
  Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-07 23:38 +0100
  Re: Float Vs Double Real Troll <real.troll@trolls.com> - 2016-08-07 18:55 -0400
    Re: Float Vs Double jameskuyper@verizon.net - 2016-08-07 16:43 -0700
      Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-07 19:36 -0700
        Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-08 04:05 +0100
          Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-07 20:41 -0700
            Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-08 11:41 +0100
              Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-08 04:23 -0700
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-08 23:45 +0100
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-10 03:26 -0700
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-11 01:00 +0100
        Re: Float Vs Double jameskuyper@verizon.net - 2016-08-08 08:52 -0700
          Re: Float Vs Double James Kuyper <jameskuyper@verizon.net> - 2016-08-08 11:58 -0400
          Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-08 10:06 -0700
      Re: Float Vs Double "James R. Kuyper" <jameskuyper@verizon.net> - 2016-08-08 19:46 -0400
    Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-07 21:29 -0400
      Re: Float Vs Double jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-08 14:04 +0200
        Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-08 09:00 -0400
          Re: Float Vs Double jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-08 18:43 +0200
            Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-08 14:34 -0400
              Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-08 12:00 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-08 16:42 -0400
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-08 14:04 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-09 08:48 -0400
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-10 03:22 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-21 18:31 -0400
                Re: Float Vs Double supercat@casperkitty.com - 2016-08-22 08:39 -0700
                Re: Float Vs Double Jean-Marc Bourguet <jm@bourguet.org> - 2016-08-22 19:29 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-22 19:24 -0400
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-23 01:01 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-22 21:58 -0400
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-23 09:38 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 08:15 -0400
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-23 15:07 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 09:40 -0400
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-23 15:14 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 10:38 -0400
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-23 17:18 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 15:47 -0400
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-23 16:39 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 11:45 -0400
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-23 21:42 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 15:52 -0400
                Re: Float Vs Double Ian Collins <ian-news@hotmail.com> - 2016-08-24 08:36 +1200
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-24 09:39 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-24 11:31 -0400
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-23 10:48 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 08:17 -0400
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-23 06:01 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 09:44 -0400
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-23 07:19 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 10:39 -0400
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-23 08:18 -0700
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-23 14:47 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 10:40 -0400
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-24 01:31 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 20:53 -0400
                Re: Float Vs Double supercat@casperkitty.com - 2016-08-23 23:20 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-24 11:32 -0400
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-24 09:46 +0200
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-24 14:53 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-24 11:35 -0400
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-24 08:57 -0700
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-24 17:36 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-24 12:50 -0400
                Re: Float Vs Double Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-24 17:26 +0100
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-24 12:51 -0400
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-24 11:33 -0400
                Re: Float Vs Double Robert Wessel <robertwessel2@yahoo.com> - 2016-08-28 02:33 -0500
                Re: Float Vs Double antispam@math.uni.wroc.pl - 2016-08-31 22:36 +0000
                Re: Float Vs Double supercat@casperkitty.com - 2016-08-31 15:51 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-31 22:42 -0400
                Re: Float Vs Double supercat@casperkitty.com - 2016-09-01 08:32 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-01 15:00 -0400
                Re: Float Vs Double supercat@casperkitty.com - 2016-09-01 13:45 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-01 20:50 -0400
                Re: Float Vs Double supercat@casperkitty.com - 2016-09-02 08:11 -0700
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 12:25 -0400
                Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-09-02 20:42 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 16:25 -0400
                Re: Float Vs Double Jean-Marc Bourguet <jm@bourguet.org> - 2016-09-03 08:43 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 10:48 -0400
                Re: Float Vs Double Jean-Marc Bourguet <jm@bourguet.org> - 2016-09-03 19:43 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 18:16 -0400
                Re: Float Vs Double asetofsymbols@gmail.com - 2016-09-08 11:18 -0700
                Re: Float Vs Double Robert Wessel <robertwessel2@yahoo.com> - 2016-09-07 19:59 -0500
                Re: Float Vs Double supercat@casperkitty.com - 2016-09-08 08:13 -0700
                Re: Float Vs Double Robert Wessel <robertwessel2@yahoo.com> - 2016-09-08 19:34 -0500
                Re: Float Vs Double supercat@casperkitty.com - 2016-09-09 07:50 -0700
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-02 23:40 -0700
                Re: Float Vs Double Jean-Marc Bourguet <jm@bourguet.org> - 2016-09-03 09:06 +0200
                Re: Float Vs Double Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 10:52 -0400
                Re: Float Vs Double Rosario19 <Ros@invalid.invalid> - 2016-08-24 08:57 +0200
                Re: Float Vs Double Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-24 01:04 -0700
    Re: Float Vs Double Ike Naar <ike@iceland.freeshell.org> - 2016-08-08 06:44 +0000
      Re: Float Vs Double Keith Thompson <kst-u@mib.org> - 2016-08-08 00:16 -0700
        Re: Float Vs Double Richard Damon <Richard@Damon-Family.org> - 2016-08-08 23:29 -0400
    Re: Float Vs Double jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-08 14:03 +0200
      Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-08 05:14 -0700
        Re: Float Vs Double BGB <cr88192@hotmail.com> - 2016-08-09 19:53 -0500
  Re: Float Vs Double "James R. Kuyper" <jameskuyper@verizon.net> - 2016-08-07 18:47 -0400
  Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-07 17:04 -0700
    Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-08 05:49 -0700
    Re: Float Vs Double Nobody <nobody@nowhere.invalid> - 2016-08-10 03:26 +0100
      Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-09 20:15 -0700
        Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-10 06:07 -0700
      Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-10 06:13 -0700
        Re: Float Vs Double David Brown <david.brown@hesbynett.no> - 2016-08-10 16:43 +0200
          Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-10 07:56 -0700
          Re: Float Vs Double supercat@casperkitty.com - 2016-08-10 08:39 -0700
            Re: Float Vs Double Keith Thompson <kst-u@mib.org> - 2016-08-10 09:56 -0700
              Re: Float Vs Double Keith Thompson <kst-u@mib.org> - 2016-08-10 10:04 -0700
                Re: Float Vs Double Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-11 07:08 -0700
                Re: Float Vs Double "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-08-11 07:15 -0700
                Re: Float Vs Double Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-12 08:11 -0700
              Re: Float Vs Double jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-10 20:38 +0200
                Re: Float Vs Double Keith Thompson <kst-u@mib.org> - 2016-08-10 12:20 -0700
                Re: Float Vs Double supercat@casperkitty.com - 2016-08-10 12:17 -0700
                Re: Float Vs Double jacobnavia <jacob@jacob.remcomp.fr> - 2016-08-10 21:48 +0200
                Re: Float Vs Double Keith Thompson <kst-u@mib.org> - 2016-08-10 13:40 -0700
              Re: Float Vs Double Ian Collins <ian-news@hotmail.com> - 2016-08-12 08:01 +1200
          Re: Float Vs Double BGB <cr88192@hotmail.com> - 2016-08-10 15:00 -0500

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