Re: [clisp-list] numbers - error in substraction

[Pascal B. <pj...@in...>]

Matthias Buelow writes:
> Pascal Bourguignon <pj...@in...> writes:
> 
> >> [1]> (- 1.1 0.9)
> >> 0.20000005
> >Common Lisp is a _practical_ language. Therefore in some aspects it's
> >very high level (it has rational numbers), but in other aspects it's
> >designed to be efficient on available hardware therefore it is
> >specified to use floating-point numbers.  And for good or for evil,
> >the reader syntax 1.1 and 0.9 correspond to floating-point numbers.
> >When you write 1.1 or 0.9, you DON'T get 11/10 or 9/10. 
> >You get: 3F8CCCCD and 3F666666 (hex)
> 
> Doesn't clisp use C doubles internally?

Not by default:

[8]> (- 1.1s0 0.9s0)
0.200005s0
[9]> (- 1.1e0 0.9e0)
0.20000005
[10]> (- 1.1d0 0.9d0)
0.20000000000000007d0
[11]> (- 1.1l0 0.9l0)
0.20000000000000000004L0
[12]> (- 1.1 0.9)
0.20000005


(and setting CUSTOM:*DEFAULT-FLOAT-FORMAT* doesn't seem to have effect
in 2.33.83).

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
Cats meow out of angst
"Thumbs! If only we had thumbs!
We could break so much!"