[lwip-devel] [bug #27352] Change ip_addr from struct to typedef (u32_t)

[Bill Auerbach]

Follow-up Comment #22, bug #27352 (project lwip):

Wasn't the point memory alignment requirements?  The original post was about
packing the ip-addr struct because there was significant overhead to have
every ip_addr access be byte-wide with ANDs, ORs and shifts.  Not packing
means you can't take the address of a casted ip_hdr pointer into payload in
any callbacks, and your point on this was well advised.  So I'm saying, don't
pass the address of an ip_addr anywhere but simply pass in a typedef ip_addr
into all functions.  If this typedef of ip_addr becomes a struct for IPv6,
fine, it will be copied by the compiler avoiding alignment problems then as
well. For IPv4, just using a typedef yo u32_t passes by value which is more
efficient.

This means that ip_addr becomes a typedef and for IPv4 it's u32_t and for
IPv6 it's some structure.  The point being is that the C code is compatible
with either typedef.

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