Re: [hybi] Performance of Vector XOR

["Len Holgate" <[e-mail]>]

Bob,

I don't have any concerns over the performance of the xor. My code is all
c++ and the performance is fine right now.

I'd just like the spec to say what's allowed and what isn't so that I can
nail my API down... No point in allowing optional server->client masking
clients will all assume it's not allowed.

Len
http://www.serverframework.com

> -----Original Message-----
> From: Bob Gezelter [mailto:[e-mail]] 
> Sent: 07 September 2011 21:31
> To: [e-mail]; Tobias Oberstein; [e-mail]
> Cc: [e-mail]
> Subject: Performance of Vector XOR
> 
> Len, Tobias, Richard,
> 
> I would recommend extreme caution on using rough JavaScript or even
> Python benchmarks as a test for the execution efficiency of 
> the masking
> operation (Note: I say this as one who is unconvinced of the 
> benefits of
> masking).
> 
> A well-written, straight vector XOR of a message should not be an
> extremely expensive operation. I would be loath to believe that modern
> processors cannot effectively perform this operation. With all due
> respect to the implementers, it is far more likely that the JavaScript
> (and quite possibly Python) use data structures and 
> representations that
> were not designed for this type of vector operation.
> 
> In a real situation, the XOR would be done in code that is likely
> written in C/C++ or a similar language. If there is a real concern on
> this issue, then the analysis should be done at the level of precisely
> what machine instructions are actually being executed. As a 
> former code
> generator writer, I can attest that it is quite easy to gain or lose
> efficiency at this level (for example, I would be unsurprised to
> discover that JavaScript and Python are doing the XOR one byte at a
> time, rather than in 64-bit chunks; that alone would account 
> for nearly
> an order of magnitude performance hit).
> 
> - Bob Gezelter, http://www.rlgsc.com
> 
>