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

[Michael Williamson]

> As I said in a mail last night: "A compromise might be to define
> offsets of members, and SMEMCPY from the correct location. An
> optimising compiler can more easily eliminate that and convert to an
> assignment where it knows it can. The situation for those using poor
> compilers could be bad though - function calls every time; and they
> may have been unaffected by the portability issue in the first place. "
>
> In other words, the price of complete portability would be poor
> performance for the vast majority of existing users. And more complex
> code.
>
> Jifl

What if you made a macro that basically did structure copying as it is
done now, but allowed it to be overridden in a sys_arch.h file?  Not
sure this would work, I'm not a coding wizard, but what about:

#define STRUCT_COPY(struct_type, inptr, outptr) \
#ifndef STRUCT_COPY_##struct_type \
memcpy(outptr, input, sizeof(struct_type)); \
#else \
STRUCT_COPY_##struct_type(inptr,outptr); \
#endif

Then guys with address-alignment challenged compilers could deal with a
non-efficient routine when they needed to and everyone else would get
the optimal solution.  Not sure if this solves the whole problem
(pointer assignment?), but you get the idea....

-Mike

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