Re: [PATCH 2/3] can: add hash based access to single EFF frame filters

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 02.04.2014 12:06, Marc Kleine-Budde wrote:

> 
> [1] After a long long long search I found a compiler (Debian clang
> version 3.4-2 (tags/RELEASE_34/final) (based on LLVM 3.4) in 32 Bit
> mode) that produces a function with more more instruction for your
> "backwards" hash compared to a "forward" hash:
> 
> 	hash = can_id;
> 	hash ^= can_id >> CAN_EFF_RCV_HASH_BITS;
> 	hash ^= can_id >> (2 * CAN_EFF_RCV_HASH_BITS);
> 
> 	return hash & ((1 << CAN_EFF_RCV_HASH_BITS) - 1);
> 
> In 64 bit mode it issues the same number of instructions, though your
> backwards hash is a byte shorter :) gcc 4.7 in contrast creates same
> number of instructions and bytes for 32 and 64 bit.
> 

Ok, I see you really had fun with this review :-)

Will change the hash function like this - and the other stuff too.

Thanks,
Oliver