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Re: Getting the exponent of an x87 float

Date 2026-09-06 12:40 +1000
Subject Re: Getting the exponent of an x87 float
Newsgroups comp.lang.forth
References (19 earlier) <117f3th$tbos$1@dont-email.me> <6a9b7cf3$1@news.ausics.net> <117h78t$1hpi9$2@dont-email.me> <6a9c4832$1@news.ausics.net> <117i84b$1tflm$1@dont-email.me>
From dxf <dxforth@gmail.com>
Message-ID <6a9cd297$1@news.ausics.net> (permalink)
Organization Ausics - https://newsgroups.ausics.net

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On 6/09/2026 9:20 am, Krishna Myneni wrote:
> 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 it fixed the error msg on input conversion from dd-io.4th - no?
 
> 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.

Perhaps.  Other than adding a routine to handle DD input, I didn't feel
the need to depart from convention.  Besides which the package was limited
to the basic four functions and there's only so much one can do with that.
I didn't have the expertise or particular interest to expand it further.

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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

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