Date: Wed, 29 Nov 2000 07:50:53 -0800 From: Julian Elischer <julian@elischer.org> To: Bruce Evans <bde@zeta.org.au> Cc: current@FreeBSD.ORG Subject: Re: slight improvement in locore.s? Message-ID: <3A2525DD.3D1E8D5A@elischer.org> References: <Pine.BSF.4.21.0011291824440.2767-100000@besplex.bde.org>
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Bruce Evans wrote:
>
> On Thu, 23 Nov 2000, Julian Elischer wrote:
>
> > locore.s includes:
> > #define ALLOCPAGES(foo) \
> > movl R(physfree), %esi ; \
> > movl $((foo)*PAGE_SIZE), %eax ; \
> > addl %esi, %eax ; \
> > movl %eax, R(physfree) ; \
> > movl %esi, %edi ; \
> > movl $((foo)*PAGE_SIZE),%ecx ; \
> > xorl %eax,%eax ; \
> > cld ; \
> > rep ; \
> > stosb
> >
> >
> > might it be a very slight optimisation to change this to:
> > #define ALLOCPAGES(foo) \
> > movl R(physfree), %esi ; \
> > movl $((foo)*PAGE_SIZE), %eax ; \
> > movl %eax, %ecx ; \
> > addl %esi, %eax ; \
> > movl %eax, R(physfree) ; \
> > movl %esi, %edi ; \
> > xorl %eax,%eax ; \
> > cld ; \
> > rep ; \
> > stosb
>
> This can be improved more (3 instructions) by not loading physfree into
> the wrong register, and depending on stosb to increment the register,
so your assembly code would look like? (just curious).
> but it should be written in C anyway. A relocation macro like R()
> should work just as well in C as in asm. In C, the above is:
>
> bzero(R(physfree), (foo) * PAGE_SIZE);
> R(physfree) += (foo) * PAGE_SIZE);
> return (R(physfree)); /* In unusual as well as wrong reg %esi. */
>
> Bruce
--
__--_|\ Julian Elischer
/ \ julian@elischer.org
( OZ ) World tour 2000
---> X_.---._/ presently in: Budapest
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