Re: [Amforth-devel] printing floats

[Leon N. M. <leo...@gm...>]

I've avoided division by reciprocal multiplication because it introduces 
rounding errors (.1 in decimal is infinitely repeating in binary). That said, 
we already have some rounding errors, so it may be worth doing -- although 
these new rounding errors do look slightly more severe.

I'll think about it -- the test you can definitely gives me some good 
information.
-Leon

On Saturday, September 04, 2010 02:01:30 pm you wrote:
> Leon, I did following - I put print"#" in f* and print"%" in f/:
> > 987654321. d>f _1e9 f*
> 
> # ok
> 
> > fs.
> 
> %%%%%%%%%%%%%%%%%9.###8###7###6###5###3###6###4E17  ok
> 
> > 987654321. d>f _1e-9 f*
> 
> # ok
> 
> > fs.
> 
> #9.###8###7###6###5###3###2###6E-1  ok
> 
> > 987654321. d>f _1e-9 f/
> 
> % ok
> 
> > fs.
> 
> %%%%%%%%%%%%%%%%%9.###8###7###6###5###4###5###9E17  ok
> 
> > 987654321. d>f _1e-18 f/
> 
> % ok
> 
> > fs.
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%9.###8###7###6###5###5###0###7E26  ok
> 
> > 987654321. d>f _1e-18 f* _1e-12 f*
> 
> ## ok
> 
> > fs.
> 
> ######################9.###8###7###6###4###9###8E-22  ok
> 
> ok
> 
> > 987654321. d>f _1e9 f* _1e12 f*
> 
> ## ok
> 
> > fs.
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%9.###8###7###6###5###3###4###5E29  ok
> 
> So when result with positive exponents E+XX the XX divisions are
> made. Therefore I changed the f/ (13ms) with f*(4ms) in the
> following routine:
> 
> \ if it's too large, make it smaller
> begin
> fdup _10 f>= \ [ 10 s>f ]
> while
> _.1 f*  \ _10 f/ \ [ 10 s>f ] <<<<<<<<< Here
> fnswap 1+ nfswap
> \  ." f>="
> repeat
> 
> So now:
> > 987654321. d>f _1e9 f* _1e12 f*
> 
> ## ok
> 
> > fs.
> 
> #############################9.###8###7###6###5###1###2###5E29  ok
> 
> > 987654321. d>f _1e-18 f* _1e-12 f*
> 
> ## ok
> 
> > fs.
> 
> ######################9.###8###7###6###4###9###8E-22  ok
> 
> 
> So now the conversion with positive exponens (previous f/) i 3x
> 
> faster:
> > : measure
> 
> oktimer-start _1 _pi f* _1e15 f* fs. timer-stop fs. ." sec";
> ok
> 
> > measure
> 
> 3.1415874:E15 4.9283066E-1 sec ok
> 
> > : measure
> 
> oktimer-start _1 _pi f* _1e-15 f* fs. timer-stop fs. ." sec";
> ok
> 
> > measure
> 
> 3.1415851E-15 5.4525948E-1 sec ok
> 
> > : measure
> 
> oktimer-start _-1 _pi f* _1e15 f* fs. timer-stop fs. ." sec";
> ok
> 
> > measure
> 
> -3.1415874:E15 4.9283066E-1 sec ok
> 
> > : measure
> 
> oktimer-start _-1 _pi f* _1e-15 f* fs. timer-stop fs. ." sec";
> ok
> 
> > measure
> 
> -3.1415851E-15 5.4525948E-1 sec ok
> 
> So all fs. are now ~0.5sec.
> I do not know why the colon in the number (:E15), but probably an
> induced bug (:-)).
> Pito