[Haskell-cafe] [Somewhat OT] Speed

David Roundy droundy at darcs.net
Tue Oct 28 17:34:04 EDT 2008

On Tue, Oct 28, 2008 at 08:55:59PM +0100, Henning Thielemann wrote:
>> For example, is integer arithmetic faster or slower than
>> floating-point?
> In principle integer arithmetic is simpler and faster. But your
> processor may do it in the same time.

Indeed.  Usually there are more integer arithmetic units, so more
integer arithmetic can be done in parallel.

>> Is addition faster or slower than multiplication?
> Multiplication can be done almost as fast as addition. This is so, 
> because a sum of n numbers can be computed much faster than n individual  
> additions.
>> How much slower are the trigonometric functions?
> division, square root are similar in complexity. exp, log, arctan can be  
> implemented with a school division like algorithm (CORDIC) and are 
> similar in performance.

Last I looked (which was quite a while back, but considerably more
recent than the 68k or Z80...), floating point division was the
surprise slow operation (close to the cost of a transcendental), with
square root being 5-10 times faster.  Generally, floating point
multiplies and adds have a throughput of 1 or 2 per clock cycle, with
most modern processors having a fused mutliply-add.

It does pay to reduce the number of divides and floating point
operations... but probably not if you're writing in Haskell.  :)


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