From: Mark Probert <probertm@...>
Date: 2002-12-12T03:15:19+09:00
Subject: Re: Proper Type for Dollar Amount


Hi, botp.

At 10:25 AM 12/11/2002 +0900, you wrote:

>Hmmm.. very clever/insightful, sir Mark. I'm putting your tip on my code
>bank ;-)

Scaled integers can be very handy in lots of situations.
I guess that we have just got so used to having floating
point available that we forget about what we lose.

For example, using scaled integers you can represent 1/3,
something that you can't do using (most) floating point
representations.

Interestingly, there are a bunch of rational approximations
for irrationals that allow you to do more "serious" math
using scaled integers:

const      ratio            error
------     -----            -----
pi         355/113          8.5e-8
sqrt(2)    19601/13860      1.5e-9
sqrt(3)    18817/10864      1.1e-9
e          28667/10564      5.5e-9
c          24559/8192       1.6e-9

I haven't done any checks to see if this will make any difference
to Ruby's performance.

Regards,


-mark.