a math question

I have a math question and a benchmark question and I'm not sure how
to benchmark it.

What I'm trying to do is use pgsql as a bayes token store for a spam
filter I'm writing.
In doing this I have a data structure with index keys and two integer
fields 'h_msgs' and 's_msgs' for each token and another pair for each
user (H_msgs, S_msgs), making four data pieces for each user-token
relationship.

for Bayes these are run through an equation of the form:
(s_msgs/S_msgs)/(s_msgs/S_msgs + h_msgs/H_msgs)
Which I currently do in perl.
In pgsql I have to modify this a bit with 'cast (s_msgs as double
precision)' or 'cast(s_msgs as real)' in order to get floating point
math.
( cast(s_msgs as double precision)/S_msgs) and so on...

Question: Is there a better way to get floating point math out of a
set of integers?

Thought occurred to me that if I let pgsql do this, it should be
considerably faster since perl is slower than C. But I don't know if
I have any good way of proving this.
The data retrieval process tends to dwarf everything else -- which
may mean I really shouldn't waste my time with this anyways.

But I was wondering if the thinking is valid, and how I might
benchmark the differences.