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From: Kuba Ober <ober.14@osu.edu>
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] [NEWBIE] is there an in-place map?
Date: Thu, 3 Jan 2008 11:01:52 -0500
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X-Spam: no; 0.00; for-loop:01 recursion:01 recursion:01 recursive:01 arrays:01 compiler:01 cheers:01 garbage:01 wrote:01 wrote:01 clearer:01 ints:01 caml-list:01 arithmetic:01 tail:01 

On Wednesday 02 January 2008, you wrote:
> Brian Hurt wrote:
> > The OP did say "in place modification.
>
> Kuba also said "the output array is given as the argument, not as a
> return value."
>
> > It depends.  If you have to use multiple references to make the for-loop
> > work, then I've seen tail recursion be faster (and clearer).
>
> Any example of a faster tail recursion?
>
> > Also, if
> > you recalculate the ending requirement every recursive call, recursion
> > can be slower (in the above for loop above, for example, Array.length is
> > gaurenteed to be called only once).
>
> I have no problems precalculating the Array.length value, or recursing
> down to 0.
>
> > Brian
>
> A little testing results in some data: for arrays of 1024 ints and
> simple arithmetic operations, I get a 9% speed increase in using a for
> loop over recursion.

It seems to be such a basic operation, I was thinking that it must be there. 
Array.map is fine and dandy, but it is a premature pessimization if used 
repeatedly unless the compiler would be very smart about it. It's one of the 
common Java pessimizations too: generating lots of garbage at the same spot 
in a tight loop.

Cheers, Kuba