Re: ipv4: Simplify ARP hash function.

[David Miller <davem@davemloft.net>]

From: Stephen Hemminger <shemminger@vyatta.com>
Date: Fri, 8 Jul 2011 16:41:28 -0700

> What about using murmur hash which has a four byte pass as well.
>   https://sites.google.com/site/murmurhash/

I'm trying to avoid multiplies that are not done in hardware on some
cpus.

Right now I'm looking at one of Thomas Wang's hashes, referenced on
Bob Jenkin's hash analysis page:

u32 hashint(u32 a)
{
	a += ~(a<<15);
	a ^=  (a>>10);
	a +=  (a<<3);
	a ^=  (a>>6);
	a += ~(a<<11);
	a ^=  (a>>16);

	return a;
}

It's 15 instructions, and produces better entropy in the low bits of
the result than the high bits, which is fine for how we'll use this
thing.