implemented features (Re: Decision time....)

Michel Talon talon at
Mon Jun 4 11:44:07 PDT 2007

Rahul Siddharthan wrote:

>>   From: "km b" <kmb810 at>
>>> On my own code (computational biology), using gcc, 32-bit binaries are
>>> 50% slower than 64-bit binaries.  (This is true of both gcc3 and gcc4.
>>> In fact, gcc 64-bit binaries are faster than 64-bit binaries generated
>>> by the Sun Studio compilers on amd64.)  That sort of speed difference
>>> is not trivial for the sort of work I do.
>>Please back your claims with empirical results. Please don't
>>generalize without finding out why 32-bit binaries are 50% slower than
>>64-bit binaries.
> Where is the generalisation?  I said "my own code", which is what I'm
> interested in.  But it also appears to be true of GSL (the GNU
> scientific library), at least the parts that I'm interested in.  I
> don't think, even if my claim was made "generally", it would be at all
> controversial.  Floating-point performance is much better in 64-bit
> mode, and there are twice as many general-purpose registers available.

I can confirm what Rahul is saying, perhaps this is no suprise since we are
both theoretical physicists. I see 64 bits machines   being *twice* faster 
than 32 bits machines (same machine, one in 32 bits Linux, the other in
64 bits Linux) on my computations, and particularly in symbolic maths
computations, e.g. running maple 32 bits and maple 64 bits, or floating
points computations. With this experience, i don't give any credence to the
computer people who pretend that there is no difference between the two
modes, or that you need >4 Gigs memory to see the difference. Our machines
have 2 Gigs and i see an enormous difference. 

Michel Talon

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