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Re: node types etc.



On Tue, Jan 16, 2001 at 02:32:29PM +0000, David Woodhouse wrote:
> 
> bjorn.wesen@xxxxxxx.com said:
> >  How can something be cheaper than a single addition ? :) 
> 
> TCP checksums aren't just a simple addition. You have to fold back into 16 

Yes.  They're a simple addition of one's-complement 16 bit units (at least
in the actual loop).

> bits. I'm told that CRC can be cheaper on 32-bit machines. A straight 
> 32-bit checksum, on the other hand, can quite possibly be cheaper than 
> either.

I don't think there's any noticeable difference, considering we're dealing
with very small blocks of data here (which our tcp checksum routines should
be optimized for anyway).

I'm not aware of any existing straight 32-bit checksum routines that work
with unaligned data (it's not hard, but it's not as easy as using the tcp
routines).

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