Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.forth > #135574

Re: Getting the exponent of an x87 float

From Krishna Myneni <krishna.myneni@ccreweb.org>
Newsgroups comp.lang.forth
Subject Re: Getting the exponent of an x87 float
Date 2026-09-05 18:20 -0500
Organization A noiseless patient Spider
Message-ID <117i84b$1tflm$1@dont-email.me> (permalink)
References (18 earlier) <6a9a1f89$1@news.ausics.net> <117f3th$tbos$1@dont-email.me> <6a9b7cf3$1@news.ausics.net> <117h78t$1hpi9$2@dont-email.me> <6a9c4832$1@news.ausics.net>

Show all headers | View raw

On 9/5/26 11:49, dxf wrote:
> On 5/09/2026 11:59 pm, Krishna Myneni wrote:
>> On 9/4/26 21:22, dxf wrote:
>>> On 5/09/2026 4:50 am, Krishna Myneni wrote:
>>>> On 9/3/26 8:31 PM, dxf wrote:
>>>>> On 4/09/2026 12:02 am, Krishna Myneni wrote:
>>>>>> On 9/3/26 07:56, dxf wrote:
>>>>>>> On 3/09/2026 9:49 pm, Krishna Myneni wrote:
>>>>>>>> On 9/2/26 19:56, dxf wrote:
>>>>>>>>> ...
>>>>>>>>> More problematic was mantissa digits extraction that could result
>>>>>>>>> in junk output:
>>>>>>>>>
>>>>>>>>>        s" 9.9999999999999999999999999999999dd" >dd CR DDFS.
>>>>>>>>>        +1.0000000000000000000000000000000 dd 1  ok
>>>>>>>>>
>>>>>>>>>        s" 9.999999999999dd" >dd CR DDFS.
>>>>>>>>>        +0.0000000000007777777777600000000 dd 0  ok
>>>>>>>>>
>>>>>>>>> It seems this was never corrected.
>>>>>>>>>
>>>>>>>>
>>>>>>>> If the fpu is not configured for double precision and round to nearest mode, the double double words will likely fail. They rely on rounding to double-precision.
>>>>>>>
>>>>>>> Tested on Win32Forth (8 byte floats) and GForth.
>>>>>>>
>>>>>>
>>>>>> Please try the kForth implementation on any of kForth-32/64/Win-32.
>>>>>
>>>>> That seems worse ;)
>>>>>
>>>>>      kForth-Win32 v 2.5.5     (Build: 2026-07-18)
>>>>>
>>>>>      Ready!
>>>>>      include ans-words
>>>>>      include ddarith
>>>>>
>>>>>      FPU base = 2   FPU precision = 53
>>>>>       ok
>>>>>      include dd_io
>>>>>
>>>>>      precision .
>>>>>      32  ok
>>>>>      s" 9.9999999999999999999999999999999dd" >dd CR DDFS.
>>>>>
>>>>>      +0.0000000000000000000000000000000 dd -314 ok
>>>>>
>>>>>      s" 9.999999999999dd" >dd CR DDFS.
>>>>>      BUF->DD: Float conversion failed
>>>>>      Line 7:  VM Error(-56):
>>>>>      s" 9.999999999999dd" >dd CR DDFS.
>>>>>
>>>>>
>>>>
>>>> These examples fail under kForth-Win32 and kForth-32 in the same way.
>>>>
>>>> Under kForth-64, the first example gives
>>>>
>>>> precision .
>>>> 32  ok
>>>> s" 9.9999999999999999999999999999999dd" >dd ddfs.
>>>> +1.0000000000000000000000000000005 dd 1 ok
>>>>
>>>> The second example gives,
>>>>
>>>> s" 9.999999999999dd" >dd DDFS.
>>>> BUF->DD: Float conversion failed
>>>> Line 402:  VM Error(-56):
>>>>
>>>> Clearly there is a problem with the >DD conversion of a decimal string to double-double precision.
>>>
>>> Trawling through my files I discovered I'd developed a solution to the
>>> general issue of DDFS. back in 2012 but had totally forgotten about.  It
>>> seems that peeling off the mantissa digits can result in negative values
>>> which then have to be corrected.  It puzzled me other users of JVN's package
>>> hadn't encountered the same.  That JVN never fixed it might be explained
>>> by his passing.
>>>
>>> The string to float parser seemed complicated so I replaced it.  FWIW
>>> here's my 2012 version cleaned up, including mods for KForth.
>>>
>>> https://pastebin.com/1UMmpkf6
>>>
>>
>> Are you sure DDFS. is the problem. In my case, I think the problem is with the decimal string to double double number conversion i.e., the problem lies in >DD and not in DDFS.
> 
> The original 'initialize' wasn't ANS compliant could fail.  The fix is:
> 
> : initialize
>      hi#  init_buffer            \ buffers
>      lo#  init_buffer
>      lo#  [CHAR] 0  +char        \ ** add **
>      lo#  [CHAR] .  +char
>      0 TO pre_dp   0 TO post_dp  \ counts
>      0 >state  ( <<hi/lo>>)         \ fsm
> ;
> 
> Your >DD should then work, after which you can test DDFS.
> 

That didn't work.

But I ran your version of ddarith/dd_io from pastebin under kForth-32 
(2.8.0). Below are the results:

=== begin output ===
include ans-words

/home/krishna/kforth/ans-words.4th
  ok
include dxforth-dd  \ code from pastebin (unchanged)
SYSTEM is redefined

Double-Double Precision FP

Testing

-1.1111222223333344444555556666600E-44
+-11.1112222233333444445555566666d-45 failed
+11.1112222.233333444445555566666d-45 failed
1.1111222223333344444555556666599E46
1.1111222223333344444555556666599E1
1.1111222223333344444555556666599E1
1.1111222223333344444555556666599E1
1.1111222223330000000000000000000E6

0.0000000000000000000000000000000E0
6.6666666666666666666666666666666E-1
9.9999999999999999999999987654324E0
-9.9999999999999900000000123456788E0
-9.9999999999990000000000000000000E0  ok

=== end output ===

This is encouraging! Tests 2 and 3 failed as they should.

Per JVN's notes, Test 5 was supposed to fail and output

+0.0000000000000000000000000000000 dd 0

due to a lack of exponent in the input string.

Your own tests are the last 5 above. I recommend sticking with the "dd" 
exponent indicator, otherwise you won't be able to differentiate double 
precision output from double double output.

--
Krishna

Back to comp.lang.forth | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-16 09:42 +1000
  Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-17 15:11 +0000
    Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-18 03:47 +1000
      Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-17 21:18 +0000
        Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-18 12:15 +1000
          Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-18 09:01 +0000
            Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-18 20:04 +1000
              Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-19 02:30 +1000
            Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-18 09:16 -0500
              Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-23 06:06 -0500
      Re: Getting the exponent of an x87 float antispam@fricas.org (Waldek Hebisch) - 2026-08-18 17:55 +0000
        Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-19 13:48 +1000
          Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-19 17:14 +1000
            Re: Getting the exponent of an x87 float peter <peter.noreply@tin.it> - 2026-08-19 09:58 +0200
              Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-19 19:14 +1000
                Re: Getting the exponent of an x87 float peter <peter.noreply@tin.it> - 2026-08-19 15:36 +0200
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-20 12:36 +1000
          Floating point (was: Getting the exponent of an x87 float) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-19 08:38 +0000
  Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-19 18:44 -0500
    Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-20 12:35 +1000
      Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-20 03:40 -0500
  Re: Getting the exponent of an x87 float albert@spenarnc.xs4all.nl - 2026-08-22 18:43 +0200
    Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-23 18:47 +1000
      Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-23 14:34 -0500
        Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-24 11:42 +1000
          Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-23 22:11 -0500
            Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-24 14:37 +1000
              Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-24 06:42 +0000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-26 01:56 +1000
                Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-25 16:24 +0000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-26 13:24 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-25 23:26 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-26 18:57 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-27 09:24 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-28 11:14 +1000
                Re: Getting the exponent of an x87 float Stephen Pelc <stephen@vfxforth.com> - 2026-08-28 10:23 +0000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-28 21:28 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 09:04 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 09:10 -0500
                Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-28 14:17 +0000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 09:41 -0500
                Re: Getting the exponent of an x87 float albert@spenarnc.xs4all.nl - 2026-08-28 19:40 +0200
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 14:00 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 14:25 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 14:40 -0500
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-08-29 12:17 +0200
                Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-29 10:35 +0000
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-08-29 15:02 +0200
                Re: Getting the exponent of an x87 float albert@spenarnc.xs4all.nl - 2026-08-29 15:51 +0200
                Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-29 14:45 +0000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-29 14:50 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-29 15:01 -0500
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-08-29 23:26 +0200
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-29 17:16 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-03 10:56 +1000
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-09-03 11:52 +0200
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-03 21:00 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-03 06:49 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-03 22:56 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-03 09:02 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-04 11:31 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-04 13:50 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-05 12:22 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-05 08:59 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-06 02:49 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-05 18:20 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-06 12:40 +1000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-06 18:57 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-06 07:36 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-06 07:42 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-07 11:00 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-06 21:16 -0500
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-09-07 08:45 +0200
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-07 21:11 +1000
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-09-07 21:30 +0200
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-07 19:09 -0500
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-09-08 14:06 +0200
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-08 12:14 -0500
                Re: Getting the exponent of an x87 float marcel hendrix <mhx@iae.nl> - 2026-09-09 02:15 +0200
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-08 14:41 +1000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-08 19:31 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-08 05:30 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-08 05:44 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-08 23:10 +1000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-09 01:03 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-08 20:49 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-09 13:31 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-09 20:02 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-09-10 12:46 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-07 17:21 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-07 22:13 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-05 21:27 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-09-05 21:55 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-29 07:38 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-30 11:12 +1000
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-29 13:18 -0500
                Re: Getting the exponent of an x87 float Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-08-28 07:25 -0500
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-28 23:43 +1000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-28 23:56 +1000
                Re: Getting the exponent of an x87 float albert@spenarnc.xs4all.nl - 2026-08-27 12:38 +0200
                Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-26 10:55 +0000
                Re: Getting the exponent of an x87 float dxf <dxforth@gmail.com> - 2026-08-26 22:55 +1000
                Re: Getting the exponent of an x87 float anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-08-26 14:29 +0000

csiph-web