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Lib: Improve IP/net hashing

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Backport some changes from branch oz-parametric-hashes. Replace naive
hash function for IPv6 addresses, fix hashing of VPNx (where upper half
of RD was ignored), fix hashing of MPLS labels (where identity was used).
This commit is contained in:
Ondrej Zajicek 2023-05-18 15:55:45 +02:00
parent 3cf91fb9eb
commit b0e97617d9
3 changed files with 75 additions and 17 deletions
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27
lib/birdlib.h
View File

@ -162,6 +162,7 @@ void bug(const char *msg, ...) NORET;
void debug(const char *msg, ...); /* Printf to debug output */
void debug_safe(const char *msg); /* Printf to debug output, async-safe */
/* Debugging */
#if defined(LOCAL_DEBUG) || defined(GLOBAL_DEBUG)
@ -196,10 +197,36 @@ asm(
);
#endif
/* Pseudorandom numbers */
u32 random_u32(void);
void random_init(void);
void random_bytes(void *buf, size_t size);
/* Hashing */
/* Constant parameter for non-parametrized hashes */
#define HASH_PARAM 2902958171u
/* Precomputed powers of HASH_PARAM */
#define HASH_PARAM1 ((u64) HASH_PARAM)
#define HASH_PARAM2 (HASH_PARAM1 * HASH_PARAM)
#define HASH_PARAM3 (HASH_PARAM2 * HASH_PARAM)
#define HASH_PARAM4 (HASH_PARAM3 * HASH_PARAM)
/* Reduce intermediate 64-bit value to final 32-bit value */
static inline u32 hash_value(u64 a)
{ return ((u32) a) ^ ((u32) (a >> 32)); }
static inline u64 u32_hash0(u32 v, u32 p, u64 acc)
{ return (acc + v) * p; }
static inline u64 u64_hash0(u64 v, u32 p, u64 acc)
{ return u32_hash0(v >> 32, p, u32_hash0(v, p, acc)); }
static inline u32 u64_hash(u64 v)
{ return hash_value(u64_hash0(v, HASH_PARAM, 0)); }
#endif

31
lib/ip.h
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@ -194,14 +194,37 @@ static inline int ipa_nonzero2(ip_addr a)
* Hash and compare functions
*/
static inline u64 ip4_hash0(ip4_addr a, u32 p, u64 acc)
{ return (acc + _I(a)) * p; }
static inline u32 ip4_hash(ip4_addr a)
{ return u32_hash(_I(a)); }
{
// return hash_value(ip4_hash0(a, HASH_PARAM, 0));
/* For some reason, the old hash works slightly better */
return u32_hash(_I(a));
}
static inline u64 ip6_hash0(ip6_addr a, u32 p, u64 acc)
{
acc += _I0(a); acc *= p;
acc += _I1(a); acc *= p;
acc += _I2(a); acc *= p;
acc += _I3(a); acc *= p;
return acc;
}
static inline u32 ip6_hash(ip6_addr a)
{
/* Returns a 32-bit hash key, although low-order bits are not mixed */
u32 x = _I0(a) ^ _I1(a) ^ _I2(a) ^ _I3(a);
return x ^ (x << 16) ^ (x << 24);
// return hash_value(ip6_hash0(a, HASH_PARAM, 0));
/* Just use the expanded form */
u64 acc =
_I0(a) * HASH_PARAM4 +
_I1(a) * HASH_PARAM3 +
_I2(a) * HASH_PARAM2 +
_I3(a) * HASH_PARAM1;
return hash_value(acc);
}
static inline int ip4_compare(ip4_addr a, ip4_addr b)

34
lib/net.h
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@ -479,39 +479,47 @@ static inline void net_copy_mpls(net_addr_mpls *dst, const net_addr_mpls *src)
{ memcpy(dst, src, sizeof(net_addr_mpls)); }
/* XXXX */
static inline u32 u64_hash(u64 a)
{ return u32_hash(a); }
static inline u32 px4_hash(ip4_addr prefix, u32 pxlen)
{ return ip4_hash(prefix) ^ (pxlen << 26); }
static inline u32 px6_hash(ip6_addr prefix, u32 pxlen)
{ return ip6_hash(prefix) ^ (pxlen << 26); }
static inline u32 net_hash_ip4(const net_addr_ip4 *n)
{ return ip4_hash(n->prefix) ^ ((u32) n->pxlen << 26); }
{ return px4_hash(n->prefix, n->pxlen); }
static inline u32 net_hash_ip6(const net_addr_ip6 *n)
{ return ip6_hash(n->prefix) ^ ((u32) n->pxlen << 26); }
{ return px6_hash(n->prefix, n->pxlen); }
static inline u32 net_hash_vpn4(const net_addr_vpn4 *n)
{ return ip4_hash(n->prefix) ^ ((u32) n->pxlen << 26) ^ u64_hash(n->rd); }
{
u64 acc = ip4_hash0(n->prefix, HASH_PARAM, 0) ^ (n->pxlen << 26);
return hash_value(u64_hash0(n->rd, HASH_PARAM, acc));
}
static inline u32 net_hash_vpn6(const net_addr_vpn6 *n)
{ return ip6_hash(n->prefix) ^ ((u32) n->pxlen << 26) ^ u64_hash(n->rd); }
{
u64 acc = ip6_hash0(n->prefix, HASH_PARAM, 0) ^ (n->pxlen << 26);
return hash_value(u64_hash0(n->rd, HASH_PARAM, acc));
}
static inline u32 net_hash_roa4(const net_addr_roa4 *n)
{ return ip4_hash(n->prefix) ^ ((u32) n->pxlen << 26); }
{ return px4_hash(n->prefix, n->pxlen); }
static inline u32 net_hash_roa6(const net_addr_roa6 *n)
{ return ip6_hash(n->prefix) ^ ((u32) n->pxlen << 26); }
{ return px6_hash(n->prefix, n->pxlen); }
static inline u32 net_hash_flow4(const net_addr_flow4 *n)
{ return ip4_hash(n->prefix) ^ ((u32) n->pxlen << 26); }
{ return px4_hash(n->prefix, n->pxlen); }
static inline u32 net_hash_flow6(const net_addr_flow6 *n)
{ return ip6_hash(n->prefix) ^ ((u32) n->pxlen << 26); }
{ return px6_hash(n->prefix, n->pxlen); }
static inline u32 net_hash_ip6_sadr(const net_addr_ip6_sadr *n)
{ return net_hash_ip6((net_addr_ip6 *) n); }
{ return px6_hash(n->dst_prefix, n->dst_pxlen); }
static inline u32 net_hash_mpls(const net_addr_mpls *n)
{ return n->label; }
{ return u32_hash(n->label); }
u32 net_hash(const net_addr *a);