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
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