From: Mike McNally <m5@tivoli.com>
Date: Sun, 15 Dec 1996 16:13:11 -0800 (PST)
To: Bill Frantz <frantz@netcom.com>
Subject: Re: ASM vs portable code [WAS: Re: Java DES breaker?]
In-Reply-To: <199612131459.GAA06660@cygnus.com>
Message-ID: <32B493D9.558F@tivoli.com>
MIME-Version: 1.0
Content-Type: text/plain


Bill Frantz wrote:
>
> In C, each separately compiled routine must re-load it from its
> memory location because they can not coordinate register usage.

There are such things as global optimizers that are quite capable of
locating heavily-used global variables.

> Another place where this global view of a program helps is in re-loads
> after calling externally compiled routines.  The compiler must assume 
> that the external routine has changed the variable 

No, it's not true that it "must" do that.  There are optimizer systems
that defer decisions until link time (the MIPS compilers for example).

That said, it's probably the case that a hand-written DES routine
could probably better a good optimizer; the size of the problem is
pretty small.  On the other hand, I suspect a specially-tuned 
optimizer that used (maybe; I'm making this up off the top of my
head) some sort of genetic techniques could find faster code sequences
than a human coder would.

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Mike McNally -- Egregiously Pointy -- Tivoli Systems, "IBM" -- Austin
mailto:m5@tivoli.com    mailto:m101@io.com    http://www.io.com/~m101
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