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Re: [gnugo-devel] engine/influence.c (and DFA)

From: Marco Scheurer
Subject: Re: [gnugo-devel] engine/influence.c (and DFA)
Date: Tue, 3 Sep 2002 17:43:06 +0200

On Tuesday, September 3, 2002, at 05:10  pm, Arend Bayer wrote:

On 3 Sep 2002, Dave Denholm wrote:

Unrolling the loop
reduced the time from 6 minutes to 5 minutes 37 seconds. (I had been
wondering whether the measured speedup had been due to it doing less
work, rather than due to the unrolling.)

What I've been wondering: Shouldn't we expect a modern compiler do do the
loop unrolling himself?

Aren't there also cases where loop unrolling has a negative effect?

Speaking of micro optimizations and speed/space trade offs, I've been wondering about these:

- There are many bi-dimensional arrays. Would it make sense to replace them by pointers to pointers? Two indirections are supposed to be faster than the arithmetic needed to access elements in a bi-directional array. The syntax to read an element is the same, but some initialization code is needed.

- Replace floats with doubles? The net effect probably depends on the processor and the compiler, and is not likely to make a huge difference. But maybe these floats could be declared as ggfloat, with an option to typedef this as float or double.

Marco Scheurer
Sen:te, Lausanne, Switzerland

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