Re: [Maxima-discuss] The decimal float package

[Michel T. <ta...@lp...>]

Le 30/11/2025 à 18:48, Richard Fateman a écrit :
> oading decfloat  via load(decfp):
> the following commands work
> bfloat(%i)
> bfloat(3)
>   but
> bfloat(3*%i) fails.
> bfloat(3*x)  fails
> bfloat(3+x) fails
>
>
> The bug occurs inside a call to dectimesbigfloat, decaddbigfloat...
> There's a test to see if any of the parts of the product or sum are 
> not convertible to decimal, in
> which case the usual (binary) bigfloat is used.
> but it then fails since it apparently cannot be converted to a bigfloat.


Indeed this happens because in decfp-core.lisp, the lisp functions 
$bfloat , bigfloatp, etc. are redefined, thus there is no way to recover 
a clean state afterwards, and when encountering bfloat(3*%i) the program 
$bfloat tries to multiply bfloat(3) by bigfloatp(%i) which returns NIL, 
hence the error message. Any other symbol like "x" does the same as %i. 
Trying to force bigfloatp to return %i instead of NIL doesn't work 
because £bfloat expects to see a list representing a bigfloat and not a 
bare symbol. So the bug comes because $bfloat doesn't understand complex 
numbers. However in the same file decfp-core.lisp there is at the end 
something supporting complex numbers, and this works.

maxima
Loading /home/michel/.maxima/maxima-init.mac
Maxima 5.48.1 https://maxima.sourceforge.io
using Lisp SBCL 2.5.8
(%i1) load(decfp);
redefining bigfloat %TAN to also work for decimal bigfloat
redefining bigfloat %LOG to also work for decimal bigfloat
redefining bigfloat %SIN to also work for decimal bigfloat
redefining bigfloat %ATAN to also work for decimal bigfloat
redefining bigfloat %COS to also work for decimal bigfloat

(%o1) /usr/local/share/maxima/5.48.1/share/numeric/decfp.lisp
(%i2) :lisp(bigfloat::bigfloat #$1+3*%i$)

+1.0b0+3.0b0*%i

Note this is in a special package :bigfloat.  Thus i think that 
inserting a proper call to this function should solve the bug.But i 
don't see any hope that other float functions work correctly after 
having loaded decfp.



-- 
Michel Talon