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New hash functions according to benchmarks posted yesterday. (The IPv6

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version has not been benchmarked yet due to insufficient test data.)
Now ipa_hash() returns a uniformely distributed 16-bit value.
This commit is contained in:
Martin Mares 1998-12-20 13:57:49 +00:00
parent a05406e69c
commit a6f250f5c6
2 changed files with 5 additions and 3 deletions
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6
lib/ipv4.h
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@ -61,10 +61,12 @@ typedef u32 ip_addr;
int ipv4_classify(u32); int ipv4_classify(u32);
u32 ipv4_class_mask(u32); u32 ipv4_class_mask(u32);
/* FIXME: Is this hash function uniformly distributed over standard routing tables? */
static inline unsigned ipv4_hash(u32 a) static inline unsigned ipv4_hash(u32 a)
{ {
return a ^ (a >> 16) ^ (a >> 24); /* Returns a 16-bit value */
a ^= a >> 16;
a ^= a << 10;
return a & 0xffff;
} }
#endif #endif

2
lib/ipv6.h
View file

@ -59,7 +59,7 @@ void ipv6_ntoh(ip_addr *);
static inline unsigned ipv6_hash(ip_addr *a) static inline unsigned ipv6_hash(ip_addr *a)
{ {
u32 x = _I0(*a) ^ _I1(*a) ^ _I2(*a) ^ _I3(*a); u32 x = _I0(*a) ^ _I1(*a) ^ _I2(*a) ^ _I3(*a);
return x ^ (x >> 16) ^ (x >> 8); return (x ^ (x >> 16) ^ (x >> 8)) & 0xffff;
} }
#endif #endif