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From: dxf <dxforth@gmail.com>
Newsgroups: comp.lang.forth
Subject: Re: FP number syntax
Date: Thu, 2 Jan 2025 00:20:53 +1100
Organization: i2pn2 (i2pn.org)
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On 1/01/2025 10:47 pm, Anton Ertl wrote:
> dxf <dxforth@gmail.com> writes:
>> On 1/01/2025 2:42 pm, Bernd Linsel wrote:
>>> It's usually implemented that DPL is reset to -1 when entering >NUMBER,
>>> each successful digit conversion increments it only if it is >= 0, and the first decimal separator encountered changes it from -1 to 0.
>>
>> Yes, in Fig-Forth.  In Swiftforth DPL is just a flag.
> 
> SwiftForth x64-Linux 4.0.0-RC89 15-Jul-2024 
> 1 dpl ? -1023  ok
> 1.234 dpl ? 3  ok
> 12 dpl ? -1022  ok

My bad.  >NUMBER increments DPL but how/when appears to vary with implementation.
Also Kitt Peak Forth (1979) DPL is for output - not input!

> Apparently SwiftForth counts every digit starting with -1024, and "."
> setting the count to 0.  So for doubles the behaviour is the same as
> that of Gforth, and testing for dpl @ 0< identifies singles on both
> systems.  lxf and VFX behave like Gforth.
> 
> So systems that implement DPL implement it similarly enough that
> programs can determine the number of digits after the decimal point.
> 
> But does anybody actually make use of DPL?  I have not seen a single
> use, ever.  Is it just some feature that someone thought up and
> implemented, and we all continued to implement it because we could and
> it was traditional?

Since >NUMBER (and previous incarnations) all increment DPL such use must
have been originally envisioned.
 
> If there has been a use at some time, is there still?  I have not seen
> complaints about the non-standardization of DPL and the
> only-terminating decimal point in Forth-94 or Forth-2012.

Pulling DPL out of systems that currently use it might result in complaints.