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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Numerical calculations: Why not use fixed point types for
 everything?
Date: Fri, 18 Jan 2013 10:52:23 -0700
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Date: 2013-01-18T10:52:23-07:00
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On 01/18/2013 10:24 AM, J-P. Rosen wrote:
> Le 18/01/2013 10:17, Ada novice a �crit :
>> I have read (John Mc Cormick: Building parallel...with Ada's book)
>> that fixed point arithmetic is faster than floating-point arithmetic
>> since integer instructions are faster
> General advice: don't assume anything about speed unless you had a
> chance to measure it.
>
> I heard a claim that with modern co-processors, floating point
> arithmetic was faster than integer arithmetic. Since the claim was by
> Robert Dewar, it is worth considering...

When I started programming FORTRAN-66 on a CDC-6400 in 1975, floating-point 
operations were done in S/W and integer operations were significantly faster. On 
modern processors with FPUs, integer operations are not necessarily faster than 
floating-point. I don't know that floating-point operations are always faster 
than integer with FPUs, though. One advantage is that FPU operations can proceed 
in parallel with CPU operations.

Pretty much everything I learned back in the good old days isn't true any more. 
In Pascal, we had to keep the universe of sets (implemented as packed arrays of 
Boolean) fairly small. But these days, with a 32-bit Integer, even

type Set is array (Integer) of Boolean;
for Set'Component_Size use 1;

will fit into physical memory on many machines!

-- 
Jeff Carter
"I wave my private parts at your aunties."
Monty Python & the Holy Grail
13