From: Joel VanderWerf <vjoel@...>
Date: 2009-06-06T12:09:17+09:00
Subject: Re: rounding errors?

Pascal J. Bourguignon wrote:
> Pete Hodgson <ruby-forum@thepete.net> writes:
> 
>> :~$ ruby -e "p ((0.29)*100).to_i"
>> 28
>>
>> Really?! I know that digital storage of floating point numbers can lead
>> to things like this, but this one seems a little extreme to me.
> 
> You may try a true Lisp instead of a Matzacred Lisp:
> 
> $ clisp -q -norc -x '(values (truncate (* 0.29 100)))'
> 29
> 

There's nothing strange here, just IEEE floats, which don't represent 
every decimal float:

irb(main):001:0> (0.29)*100
=> 29.0
irb(main):002:0> ((0.29)*100).to_i
=> 28
irb(main):003:0> ((0.29)*100).round
=> 29
irb(main):004:0> ((0.29)*100).floor
=> 28
irb(main):006:0> "%20.18f" % ((0.29)*100)
=> "28.999999999999996447"
irb(main):007:0> "%20.18f" % 0.29
=> "0.289999999999999980"

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407