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treetrie-2015
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Using a non-stupid hash function is EXTREMELY important

This commit is contained in:
Tony Garnock-Jones 2015-06-30 16:56:29 -04:00
parent 4fda08adc0
commit 08f2400e49
1 changed files with 19 additions and 32 deletions
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51
treetrie.c
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@ -10,31 +10,31 @@
typedef uint32_t tt_hash_t;
/* /\* Customized special-purpose fasthash variation *\/ */
/* #define mix(h) ({ \ */
/* (h) ^= (h) >> 23; \ */
/* (h) *= 0x2127599bf4325c37ULL; \ */
/* (h) ^= (h) >> 47; }) */
/* static inline uint64_t fasthash_4_ints(uint32_t v1, uint32_t v2, uint32_t v3, uint32_t v4) { */
/* const uint64_t m = 0x880355f21e6d1965ULL; */
/* uint64_t h = (16 * m); */
/* uint64_t v; */
/* v = (((uint64_t) v2) << 32) | v1; */
/* h ^= mix(v); */
/* h *= m; */
/* v = (((uint64_t) v4) << 32) | v3; */
/* h ^= mix(v); */
/* h *= m; */
/* return mix(h); */
/* } */
/* Customized special-purpose fasthash variation */
#define mix(h) ({ \
(h) ^= (h) >> 23; \
(h) *= 0x2127599bf4325c37ULL; \
(h) ^= (h) >> 47; })
static inline uint64_t fasthash_4_ints(uint32_t v1, uint32_t v2, uint32_t v3, uint32_t v4) {
const uint64_t m = 0x880355f21e6d1965ULL;
uint64_t h = (16 * m);
uint64_t v;
v = (((uint64_t) v2) << 32) | v1;
h ^= mix(v);
h *= m;
v = (((uint64_t) v4) << 32) | v3;
h ^= mix(v);
h *= m;
return mix(h);
}
static inline tt_hash_t hash(uint32_t tag,
uint32_t index,
tt_node_ptr_t a,
tt_node_ptr_t b)
{
/* uint64_t x = fasthash_4_ints(tag, index, a, b); */
/* return x - (x >> 32); */
uint64_t x = fasthash_4_ints(tag, index, a, b);
return x - (x >> 32);
/* uint32_t keyblock[4] = { tag, */
/* index, */
@ -42,19 +42,6 @@ static inline tt_hash_t hash(uint32_t tag,
/* b }; */
/* assert(sizeof(keyblock) == 4 * sizeof(uint32_t)); */
/* return (tt_hash_t) fasthash32(keyblock, sizeof(keyblock), 0); */
/* uint64_t x = tag; */
/* x = (x << 8) ^ index; */
/* x = (x << 8) ^ a; */
/* x = (x << 8) ^ b; */
/* return x - (x >> 32); */
uint64_t x = index * 11;
x *= 11;
x ^= a;
x *= 11;
x ^= b * tag;
return x - (x >> 32);
}
static inline tt_hash_t tt_hash_node(tt_arena_t *a, tt_node_ptr_t p) {