svn commit: r212064 - head/sys/boot/pc98/boot2
jhb at freebsd.org
Tue Aug 31 20:22:02 UTC 2010
On Tuesday, August 31, 2010 3:53:54 pm Dimitry Andric wrote:
> On 2010-08-31 21:37, John Baldwin wrote:
> >> - return *(p + 0x401) * 128 * 1024 + *(u_int16_t *)(p + 0x594) * 1024
> >> + return *p * 128 * 1024 + *(u_int16_t *)(p + (0x594 - 0x401)) * 1024
> >> }
> > Perhaps replace '(p + 0x594 - 0x401)' with just 'PTOV(0x594)'?
> > I would actually find it cleaner to remove 'p' altogether perhaps:
> > return (*(u_char *)PTOV(0x401) * 128 * 1024 +
> > *(uint16_t *)PTOV(0x594) * 1024 * 1024);
> Yes, I attempted this variation at first, but it made the code bigger,
> which I wanted to avoid: it went from "11 bytes available" to "7 bytes"
> I tried several semantically equivalent permutations of the expression,
> and the one I committed gave no increase or decrease in code size.
> Apparently the code size produced by gcc is very sensitive to even
> minimal changes. For example, a lot of the PTOV() pointer dereferences
> should really be qualified with 'volatile', but that even causes boot2
> to become too big to fit!
> If the 4 extra bytes are no problem, then I would be glad to change it
> to the above expression, though. It is certainly clearer. :)
I would go with cleaner as long as it fits. I would only resort to weird
tricks such as the 'p' one used previously if they are actually needed.
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