Re: ntohs/ntohl and bitops

[David S. Miller]

From: Ulrich Drepper <drepper@xxxxxxxxxx>
Date: Tue, 10 Jan 2006 14:02:52 -0800

> I just saw this in a patch:
> 
> +               if (ntohs(ih->frag_off) & IP_OFFSET)
> +                       return EBT_NOMATCH;
> 
> This isn't optimal, it requires a byte switch little endian machines.
> The compiler isn't smart enough.  It would be better to use
> 
>      if (ih->frag_off & ntohs(IP_OFFSET))
> 
> where the byte-swap can be done at compile time.  This is kind of ugly,
> I guess, so maybe a dedicate macro
> 
>     net_host_bit_p(ih->frag_off, IP_OFFSET)

The first suggestion isn't considered ugly, and the best form is:

	if (ih->frag_off & __constant_htons(IP_OFFSET))

I'll fix that up when I get a chance, thanks for catching it Uli.
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