diff options
Diffstat (limited to 'erts/emulator/beam/hash.h')
-rw-r--r-- | erts/emulator/beam/hash.h | 66 |
1 files changed, 57 insertions, 9 deletions
diff --git a/erts/emulator/beam/hash.h b/erts/emulator/beam/hash.h index d319aaca83..4e8eb6594b 100644 --- a/erts/emulator/beam/hash.h +++ b/erts/emulator/beam/hash.h @@ -18,16 +18,16 @@ * %CopyrightEnd% */ -/* -** General hash functions -** -*/ +/** + * General hash functions + * + **/ #ifndef __HASH_H__ #define __HASH_H__ #include "sys.h" -typedef unsigned long HashValue; +typedef UWord HashValue; typedef struct hash Hash; typedef int (*HCMP_FUN)(void*, void*); @@ -38,6 +38,7 @@ typedef void (*HFREE_FUN)(void*); typedef void* (*HMALLOC_FUN)(int,size_t); typedef void (*HMFREE_FUN)(int,void*); typedef int (*HMPRINT_FUN)(fmtfn_t,void*,char*, ...); +typedef void (*HFOREACH_FUN)(void *, void *); /* ** This bucket must be placed in top of @@ -75,11 +76,10 @@ struct hash int is_allocated; /* 0 iff hash structure is on stack or is static */ int meta_alloc_type; /* argument to pass to meta_alloc and meta_free */ char* name; /* Table name (static string, for debugging) */ - int size; /* Number of slots */ + int shift; /* How much to shift the hash value */ + int max_shift; /* Never shift more than this value */ int shrink_threshold; int grow_threshold; - int size_ix; /* Size index in size table */ - int min_size_ix; /* Never shrink table smaller than this */ int nobjs; /* Number of objects in table */ HashBucket** bucket; /* Vector of bucket pointers (objects) */ }; @@ -96,6 +96,54 @@ void* hash_get(Hash*, void*); void* hash_put(Hash*, void*); void* hash_erase(Hash*, void*); void* hash_remove(Hash*, void*); -void hash_foreach(Hash*, void (*func)(void *, void *), void *); +void hash_foreach(Hash*, HFOREACH_FUN, void *); + +ERTS_GLB_INLINE Uint hash_get_slot(Hash *h, HashValue hv); +ERTS_GLB_INLINE void* hash_fetch(Hash *, void*, H_FUN, HCMP_FUN); + +#if ERTS_GLB_INLINE_INCL_FUNC_DEF + +ERTS_GLB_INLINE Uint +hash_get_slot(Hash *h, HashValue hv) +{ + /* This slot mapping function uses fibonacci hashing in order to + * protect itself against a very bad hash function. This is not + * a hash function, so the user of hash.h should still spend time + * to figure out a good hash function for its data. + * + * See https://probablydance.com/2018/06/16/fibonacci-hashing-the-optimization-that-the-world-forgot-or-a-better-alternative-to-integer-modulo/ + * for some thoughts and ideas about fibonacci hashing. + */ + + /* This is not strictly part of the fibonacci hashing algorithm + * but it does help to spread the values of the mapping function better. + */ + hv ^= hv >> h->shift; +#ifdef ARCH_64 + /* 2^64 / 1.61803398875 = 11400714819323198485.... */ + return (UWORD_CONSTANT(11400714819323198485) * hv) >> h->shift; +#else + /* 2^32 / 1.61803398875 = 2654435769.... */ + return (UWORD_CONSTANT(2654435769) * hv) >> h->shift; +#endif +} + +ERTS_GLB_INLINE void* hash_fetch(Hash *h, void* tmpl, H_FUN hash, HCMP_FUN cmp) +{ + HashValue hval = hash(tmpl); + Uint ix = hash_get_slot(h, hval); + HashBucket* b = h->bucket[ix]; + ASSERT(h->fun.hash == hash); + ASSERT(h->fun.cmp == cmp); + + while(b != (HashBucket*) 0) { + if ((b->hvalue == hval) && (cmp(tmpl, (void*)b) == 0)) + return (void*) b; + b = b->next; + } + return (void*) 0; +} + +#endif /* ERTS_GLB_INLINE_INCL_FUNC_DEF */ #endif |