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Experiment with some really dumb hash functions

This commit is contained in:
Tony Garnock-Jones 2015-06-30 00:05:29 -04:00
parent b0ec92798a
commit f0b1d691ea
1 changed files with 39 additions and 6 deletions
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45
treetrie.c
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@ -8,17 +8,50 @@
#include "treetrie.h"
#include "fasthash.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_idx_t a,
tt_node_idx_t b)
{
uint32_t keyblock[4] = { tag,
index,
a,
b };
assert(sizeof(keyblock) == 4 * sizeof(uint32_t));
return (tt_hash_t) fasthash32(keyblock, sizeof(keyblock), 0);
/* uint64_t x = fasthash_4_ints(tag, index, a, b); */
/* return x - (x >> 32); */
/* uint32_t keyblock[4] = { tag, */
/* index, */
/* a, */
/* 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 = tag;
x ^= index * 11;
x ^= a * 11;
x ^= b * 11;
return x - (x >> 32);
}
inline tt_hash_t tt_hash_node(tt_arena_t *a, tt_node_idx_t i) {