Hash functions how they work in kernel?

["rahul N." <rahul8143@xxxxxxxxx>]

hello,
 I am studying hash functions in route.c kernel file
rt_hash_rnd = (int) ((num_physpages ^ (num_physpages>>8)) ^ (jiffies ^
(jiffies >> 7)));
 where rt_hash_rnd is unsigned long 

rt_hash_rnd is used in 
static unsigned int rt_hash_code(u32 daddr, u32 saddr, u8 tos)
{
	return (jhash_3words(daddr, saddr, (u32) tos, rt_hash_rnd)
		& rt_hash_mask);
}

 And what get_random_bytes does in route.c file?
get_random_bytes(&rt_hash_rnd, 4);
then how can 
        I am newbie in kernel analysis please help to know uses of
hash functions in kernel.
regards,
rahul.

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