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SubjectRe: [OFFTOPIC?] Re: 2.2.x kernels missend odd-sized ICMP pa
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Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> said:
> Horst von Brand <vonbrand@sleipnir.valparaiso.cl> writes:
> |> (This is an excerpt from ping.c:in_cksum in netkit-0.10, sent to me by
> |> Petr Vandrovec):

> |> register u_short *w = addr;
> |> register int sum = 0;
> |> u_short answer = 0;
> |> ....
> |> *(u_char*)(&answer) = *(u_char*)w;
> |> sum += answer;
> |>
> |> This is a dumb way to write this.
> |>
> |> egcs-19990405 generates code that gets the right value, others (including
> |> egcs-1.0.3 used to build RedHat-5.2, AFAIKS) break, as they don't respect
> |> the initialization and put a random byte in the higher half.
> |>
> |> A better way to write the above is just:
> |>
> |> sum += *(u_char*)w;
>
> This is not the same.

You are absolutely right: Endianness enters here. This should be:

#if __BYTE_ORDER == __LITTLE_ENDIAN
sum += *(u_char *)w;
#else
sum += (*(u_char *)w) << 8;
#endif
--
Horst von Brand vonbrand@sleipnir.valparaiso.cl
Casilla 9G, Viña del Mar, Chile +56 32 672616

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