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[PPPOE]: Improve hashing function in hash_item().

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The new code produces the same results as the old version and is
~ 3 to 6 times faster for 4-bit hashes on the CPUs I tested.

Signed-off-by: Florian Zumbiehl <florz@florz.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Zumbiehl 2007-07-31 13:47:57 -07:00 committed by David S. Miller
parent 48b8d78315
commit f1543f8b83
1 changed files with 15 additions and 10 deletions
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25
drivers/net/pppoe.c
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@ -108,19 +108,24 @@ static inline int cmp_addr(struct pppoe_addr *a, unsigned long sid, char *addr)
(memcmp(a->remote,addr,ETH_ALEN) == 0));
}
static int hash_item(unsigned long sid, unsigned char *addr)
#if 8%PPPOE_HASH_BITS
#error 8 must be a multiple of PPPOE_HASH_BITS
#endif
static int hash_item(unsigned int sid, unsigned char *addr)
{
char hash = 0;
int i, j;
unsigned char hash = 0;
unsigned int i;
for (i = 0; i < ETH_ALEN ; ++i) {
for (j = 0; j < 8/PPPOE_HASH_BITS ; ++j) {
hash ^= addr[i] >> ( j * PPPOE_HASH_BITS );
}
for (i = 0 ; i < ETH_ALEN ; i++) {
hash ^= addr[i];
}
for (i = 0 ; i < sizeof(sid_t)*8 ; i += 8 ){
hash ^= sid>>i;
}
for (i = 8 ; (i>>=1) >= PPPOE_HASH_BITS ; ) {
hash ^= hash>>i;
}
for (i = 0; i < (sizeof(unsigned long)*8) / PPPOE_HASH_BITS ; ++i)
hash ^= sid >> (i*PPPOE_HASH_BITS);
return hash & ( PPPOE_HASH_SIZE - 1 );
}