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From: Bill Findlay <yaldnif.w@blueyonder.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: 64 bit codes
Date: Tue, 27 Sep 2011 16:49:34 +0100
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Date: 2011-09-27T16:49:34+01:00
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On 27/09/2011 15:50, in article
cec56016-8606-484b-810b-3cdf1e0fcc48@v9g2000vbp.googlegroups.com, "Ludovic
Brenta" <ludovic@ludovic-brenta.org> wrote:

> Mok-Kong Shen wrote on comp.lang.ada:
>> For on 64-bit hardware a native 64-bit arithmetic
>> operation shouldn't last very much longer than a corresponding 32-bit
>> opeartion, I would think.
> 
> Only a benchmark can tell.  It is true that individual 64-bit machine
> instructions are usually just as fast as their 32-bit counterparts but
> 64-bit words use up twice as much memory and, especially, cache memory
> as 32-bit words.  The 64-bit ISA has 16 extra registers that may or
> may not compensate for the increased cache pressure and decreased code
> locality in your particular case.

My KDF9 emulator is speeded up by a factor of *more than* two by 64-bit
mode.  This is because its integer and logical operands are predominantly
more than 32 bits in size.  Pointers are used, but form a negligible part of
the storage space and computational effort.

So, while your caveats are of course valid, there certainly are workloads
that benefit greatly from working in 64 bits.

-- 
Bill Findlay
with blueyonder.co.uk;
use  surname & forename;