On Tuesday 2009-03-24 22:18, David Miller wrote:
>> >
>> >Arches without efficient unaligned access can still perform a loop
>> >assuming 16bit alignment in ifname_compare()
>>
>> Allow me some skepticism, but the code looks pretty much like a
>> standard memcmp.
>
>memcmp() can't make any assumptions about alignment.
>Whereas we _know_ this thing is exactly 16-bit aligned.
>
>All of the optimized memcmp() implementations look for
>32-bit alignment and punt to byte at a time comparison
>loops if things are not aligned enough.
Yes, I seem to remember glibc doing something like
if ((addr & 0x03) != 0) {
// process single bytes (increment addr as you go)
// until addr & 0x03 == 0.
}
/* optimized loop here. also increases addr */
if ((addr & 0x03) != 0)
// still bytes left after loop - process on a per-byte basis
Is the cost of testing for non-4-divisibility expensive enough
to warrant not usnig memcmp?
Irrespective of all that, I think putting the interface comparison
code should be agglomerated in a function/header so that it is
replicated across iptables, ip6tables, ebtables, arptables, etc.
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