RE: RE: [lwip-users] Sizes

[John Kennedy]

Well, just for fun I switched to algorithm 3 and got a 100Kbits/s improvement.

John


 
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John Kennedy


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-----Original Message-----
From: Simon Goldschmidt [mailto:address@hidden
Sent: Thursday, May 28, 2009 1:16 AM
To: Mailing list for lwIP users
Subject: Re: RE: [lwip-users] Sizes


> BTW which checksum algorithm did base your
> assembly code on?  Does anyone know which of the checksum algorithms is the
> fastest?

Unfortunately, that depends largely on your platform. The best thing to do is 
to try all of them: call them in a loop on a data buffer that is bigger than 
your caches and see which one finishes first.

> I'm a little surprised that other than the call overhead that an
> assembly version of memcpy is much faster than what the complier produces 
> from the library?

The difference here is not C or assembly but 'standard' library (written in C, 
used on many platforms) or hand-written code that performs well on your 
specific platform. And let me tell you there *is* room for improvement here. 
For example, some C libraries use byte-by-byte copy if compiled with the 
'wrong' options... Nevertheless, the standard library often is not too bad when 
copying a well-aligned source to a well-aligned destination.

Simon
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