[BRIDGE] Unaligned access on IA64 when comparing ethernet addresses

Eric Dumazet dada1 at cosmosbay.com
Thu Apr 19 07:14:23 PDT 2007


On Wed, 18 Apr 2007 13:04:22 -0700 (PDT)
David Miller <davem at davemloft.net> wrote:

> 
> Although I don't think gcc does anything fancy since we don't
> use memcmp().  It's a tradeoff, we'd like to use unsigned long
> comparisons when both objects are aligned correctly but we also
> don't want it to use any more than one potentially mispredicted
> branch.

Again, memcmp() *cannot* be optimized, because its semantic is to compare bytes.

memcpy() can take into account alignement if known at compile time, not memcmp()

http://lists.openwall.net/netdev/2007/03/13/31


> 
> We could add some alignment tests to the ethernet address
> comparison code, but it's probably more trouble than it's
> worth.
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-- 
Eric Dumazet <dada1 at cosmosbay.com>



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