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I'm sure it's been discussed a few times, but here we go.... single-precision floats
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Date: -- (:)
From: Asfand Yar Qazi <email@a...>
Subject: I'm sure it's been discussed a few times, but here we go.... single-precision floats
Hi,

I recently performed some tests on GNU C++, and found that (for a small fast
fourier transform operation anyway) double precision out-performs single
precision floating point.

However, on the Ogre 3D engine forum, I had a lengthy discussion and a
conclusion was reached that the reason single-precision floats are preferred
for games (and I assume all high-performance applications that require huge
amounts of data) is that more of them can fit into the cache of the processor.

All the OCaml discussions about floating point precision I have seen so far
evolve around how fast operations are performed on them - but the critical
thing for things like collision detection, etc. in games is the amount of data
that can fit into the CPU cache and be operated on before the cache must be
reloaded.  Obviously, twice as many single precision floats can fit into any
CPU's cache than double precision floats.

We're talking huge dynamic data structures with millions of floating point
coordinates that all have to be iterated over many times a second - preferably
by using multithreaded algorithms, so that multiple CPUs can be used
efficiently.  Since doing this sort of work (i.e. parallel computing) in C++
is a pain in the **** ('scuse my French :-), I want to learn a language that
will make it easy and less error-prone - hence my study of OCaml.

So, is there any way (I'm thinking similar to 'nativeint') to use floats in
OCaml to maximize the data that can be stored and operated on in the CPUs 
cache such that system memory is accessed as little as possible?

Thanks