Re: strange behaviour of (floor .)

[Paul Emsley]

address@hidden wrote:
> Hej all :)
>
> I'm a little confused by the results of (floor .) in a simple
> computation to get the fractional part of a monetary value. Maybe
> someone can comment on this, as especially in the last test case below
> the results seem very strange to me... 
>
> The starting point is:
> guile> (rationalize (floor (* (- 12.34 (floor 12.34)) 100)) .0)
> 33
>
> The actual result shoud be 34.
>
>   

That's one of the answers you will get if you use a computer to 
calculate the results.
33 is the other.

floor is working fine.

Consider the following:

(floor (* (- 12.34000000000001 (floor 12.34)) 100))
(floor (* (- 12.33999999999999 (floor 12.34)) 100))


Given that floating point number storage is not precise, different 
values is entirely reasonable.  You have to be a bit more sophisticated 
in your floor usage.


Paul.