Re: [lwip-users] Problem With dns.c Using 32-Bit Compilers

[Alain M.]

Grubb, Jared escreveu:
> I'm not sure which ARM processor you're referring to, but that can't actually 
> be true. By definition in the C standard, every compiler is guaranteed to have 
> byte access anywhere it wants (IIRC, a byte is defined as the minimal unit 
> addressable on the architecture). The fun part is that a byte (as defined by 
> the C standard) is not guaranteed to have 8-bits!

That is correct... and not :(

ARM7 and ARM9r4 do not have physical byte access, that is what I meant. 
So if the compiler wants byte access, it will do whatever it takes to 
get the byte, even worse to write it. If you compute pipeline misses, it 
gets a mess.

There is a very interesting chapter in my ARM book about how to write a 
program in C in a manner that the compiled code will be efficient. And 
it is very interesting to see the code generated in Eclipse debugging.

I gess that the same but happen in other 16/32 bit achitectures.

So, this is a case where a specially written macro can make a big 
difference. One advantage of TCP/IP, is that it was originaly written 
for mainframes with the same problem and almost averything in the 
headers is inside 32 bit words.

Alain