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Diffstat (limited to 'libiberty/hashtab.c')
| -rw-r--r-- | libiberty/hashtab.c | 990 |
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diff --git a/libiberty/hashtab.c b/libiberty/hashtab.c new file mode 100644 index 000000000..dfaec0f31 --- /dev/null +++ b/libiberty/hashtab.c @@ -0,0 +1,990 @@ +/* An expandable hash tables datatype. + Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004, 2009, 2010 + Free Software Foundation, Inc. + Contributed by Vladimir Makarov (vmakarov@cygnus.com). + +This file is part of the libiberty library. +Libiberty is free software; you can redistribute it and/or +modify it under the terms of the GNU Library General Public +License as published by the Free Software Foundation; either +version 2 of the License, or (at your option) any later version. + +Libiberty is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with libiberty; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor, +Boston, MA 02110-1301, USA. */ + +/* This package implements basic hash table functionality. It is possible + to search for an entry, create an entry and destroy an entry. + + Elements in the table are generic pointers. + + The size of the table is not fixed; if the occupancy of the table + grows too high the hash table will be expanded. + + The abstract data implementation is based on generalized Algorithm D + from Knuth's book "The art of computer programming". Hash table is + expanded by creation of new hash table and transferring elements from + the old table to the new table. */ + +#ifdef HAVE_CONFIG_H +#include "config.h" +#endif + +#include <sys/types.h> + +#ifdef HAVE_STDLIB_H +#include <stdlib.h> +#endif +#ifdef HAVE_STRING_H +#include <string.h> +#endif +#ifdef HAVE_MALLOC_H +#include <malloc.h> +#endif +#ifdef HAVE_LIMITS_H +#include <limits.h> +#endif +#ifdef HAVE_INTTYPES_H +#include <inttypes.h> +#endif +#ifdef HAVE_STDINT_H +#include <stdint.h> +#endif + +#include <stdio.h> + +#include "libiberty.h" +#include "ansidecl.h" +#include "hashtab.h" + +#ifndef CHAR_BIT +#define CHAR_BIT 8 +#endif + +static unsigned int higher_prime_index (unsigned long); +static hashval_t htab_mod_1 (hashval_t, hashval_t, hashval_t, int); +static hashval_t htab_mod (hashval_t, htab_t); +static hashval_t htab_mod_m2 (hashval_t, htab_t); +static hashval_t hash_pointer (const void *); +static int eq_pointer (const void *, const void *); +static int htab_expand (htab_t); +static PTR *find_empty_slot_for_expand (htab_t, hashval_t); + +/* At some point, we could make these be NULL, and modify the + hash-table routines to handle NULL specially; that would avoid + function-call overhead for the common case of hashing pointers. */ +htab_hash htab_hash_pointer = hash_pointer; +htab_eq htab_eq_pointer = eq_pointer; + +/* Table of primes and multiplicative inverses. + + Note that these are not minimally reduced inverses. Unlike when generating + code to divide by a constant, we want to be able to use the same algorithm + all the time. All of these inverses (are implied to) have bit 32 set. + + For the record, here's the function that computed the table; it's a + vastly simplified version of the function of the same name from gcc. */ + +#if 0 +unsigned int +ceil_log2 (unsigned int x) +{ + int i; + for (i = 31; i >= 0 ; --i) + if (x > (1u << i)) + return i+1; + abort (); +} + +unsigned int +choose_multiplier (unsigned int d, unsigned int *mlp, unsigned char *shiftp) +{ + unsigned long long mhigh; + double nx; + int lgup, post_shift; + int pow, pow2; + int n = 32, precision = 32; + + lgup = ceil_log2 (d); + pow = n + lgup; + pow2 = n + lgup - precision; + + nx = ldexp (1.0, pow) + ldexp (1.0, pow2); + mhigh = nx / d; + + *shiftp = lgup - 1; + *mlp = mhigh; + return mhigh >> 32; +} +#endif + +struct prime_ent +{ + hashval_t prime; + hashval_t inv; + hashval_t inv_m2; /* inverse of prime-2 */ + hashval_t shift; +}; + +static struct prime_ent const prime_tab[] = { + { 7, 0x24924925, 0x9999999b, 2 }, + { 13, 0x3b13b13c, 0x745d1747, 3 }, + { 31, 0x08421085, 0x1a7b9612, 4 }, + { 61, 0x0c9714fc, 0x15b1e5f8, 5 }, + { 127, 0x02040811, 0x0624dd30, 6 }, + { 251, 0x05197f7e, 0x073260a5, 7 }, + { 509, 0x01824366, 0x02864fc8, 8 }, + { 1021, 0x00c0906d, 0x014191f7, 9 }, + { 2039, 0x0121456f, 0x0161e69e, 10 }, + { 4093, 0x00300902, 0x00501908, 11 }, + { 8191, 0x00080041, 0x00180241, 12 }, + { 16381, 0x000c0091, 0x00140191, 13 }, + { 32749, 0x002605a5, 0x002a06e6, 14 }, + { 65521, 0x000f00e2, 0x00110122, 15 }, + { 131071, 0x00008001, 0x00018003, 16 }, + { 262139, 0x00014002, 0x0001c004, 17 }, + { 524287, 0x00002001, 0x00006001, 18 }, + { 1048573, 0x00003001, 0x00005001, 19 }, + { 2097143, 0x00004801, 0x00005801, 20 }, + { 4194301, 0x00000c01, 0x00001401, 21 }, + { 8388593, 0x00001e01, 0x00002201, 22 }, + { 16777213, 0x00000301, 0x00000501, 23 }, + { 33554393, 0x00001381, 0x00001481, 24 }, + { 67108859, 0x00000141, 0x000001c1, 25 }, + { 134217689, 0x000004e1, 0x00000521, 26 }, + { 268435399, 0x00000391, 0x000003b1, 27 }, + { 536870909, 0x00000019, 0x00000029, 28 }, + { 1073741789, 0x0000008d, 0x00000095, 29 }, + { 2147483647, 0x00000003, 0x00000007, 30 }, + /* Avoid "decimal constant so large it is unsigned" for 4294967291. */ + { 0xfffffffb, 0x00000006, 0x00000008, 31 } +}; + +/* The following function returns an index into the above table of the + nearest prime number which is greater than N, and near a power of two. */ + +static unsigned int +higher_prime_index (unsigned long n) +{ + unsigned int low = 0; + unsigned int high = sizeof(prime_tab) / sizeof(prime_tab[0]); + + while (low != high) + { + unsigned int mid = low + (high - low) / 2; + if (n > prime_tab[mid].prime) + low = mid + 1; + else + high = mid; + } + + /* If we've run out of primes, abort. */ + if (n > prime_tab[low].prime) + { + fprintf (stderr, "Cannot find prime bigger than %lu\n", n); + abort (); + } + + return low; +} + +/* Returns a hash code for P. */ + +static hashval_t +hash_pointer (const PTR p) +{ + return (hashval_t) ((intptr_t)p >> 3); +} + +/* Returns non-zero if P1 and P2 are equal. */ + +static int +eq_pointer (const PTR p1, const PTR p2) +{ + return p1 == p2; +} + + +/* The parens around the function names in the next two definitions + are essential in order to prevent macro expansions of the name. + The bodies, however, are expanded as expected, so they are not + recursive definitions. */ + +/* Return the current size of given hash table. */ + +#define htab_size(htab) ((htab)->size) + +size_t +(htab_size) (htab_t htab) +{ + return htab_size (htab); +} + +/* Return the current number of elements in given hash table. */ + +#define htab_elements(htab) ((htab)->n_elements - (htab)->n_deleted) + +size_t +(htab_elements) (htab_t htab) +{ + return htab_elements (htab); +} + +/* Return X % Y. */ + +static inline hashval_t +htab_mod_1 (hashval_t x, hashval_t y, hashval_t inv, int shift) +{ + /* The multiplicative inverses computed above are for 32-bit types, and + requires that we be able to compute a highpart multiply. */ +#ifdef UNSIGNED_64BIT_TYPE + __extension__ typedef UNSIGNED_64BIT_TYPE ull; + if (sizeof (hashval_t) * CHAR_BIT <= 32) + { + hashval_t t1, t2, t3, t4, q, r; + + t1 = ((ull)x * inv) >> 32; + t2 = x - t1; + t3 = t2 >> 1; + t4 = t1 + t3; + q = t4 >> shift; + r = x - (q * y); + + return r; + } +#endif + + /* Otherwise just use the native division routines. */ + return x % y; +} + +/* Compute the primary hash for HASH given HTAB's current size. */ + +static inline hashval_t +htab_mod (hashval_t hash, htab_t htab) +{ + const struct prime_ent *p = &prime_tab[htab->size_prime_index]; + return htab_mod_1 (hash, p->prime, p->inv, p->shift); +} + +/* Compute the secondary hash for HASH given HTAB's current size. */ + +static inline hashval_t +htab_mod_m2 (hashval_t hash, htab_t htab) +{ + const struct prime_ent *p = &prime_tab[htab->size_prime_index]; + return 1 + htab_mod_1 (hash, p->prime - 2, p->inv_m2, p->shift); +} + +/* This function creates table with length slightly longer than given + source length. Created hash table is initiated as empty (all the + hash table entries are HTAB_EMPTY_ENTRY). The function returns the + created hash table, or NULL if memory allocation fails. */ + +htab_t +htab_create_alloc (size_t size, htab_hash hash_f, htab_eq eq_f, + htab_del del_f, htab_alloc alloc_f, htab_free free_f) +{ + return htab_create_typed_alloc (size, hash_f, eq_f, del_f, alloc_f, alloc_f, + free_f); +} + +/* As above, but uses the variants of ALLOC_F and FREE_F which accept + an extra argument. */ + +htab_t +htab_create_alloc_ex (size_t size, htab_hash hash_f, htab_eq eq_f, + htab_del del_f, void *alloc_arg, + htab_alloc_with_arg alloc_f, + htab_free_with_arg free_f) +{ + htab_t result; + unsigned int size_prime_index; + + size_prime_index = higher_prime_index (size); + size = prime_tab[size_prime_index].prime; + + result = (htab_t) (*alloc_f) (alloc_arg, 1, sizeof (struct htab)); + if (result == NULL) + return NULL; + result->entries = (PTR *) (*alloc_f) (alloc_arg, size, sizeof (PTR)); + if (result->entries == NULL) + { + if (free_f != NULL) + (*free_f) (alloc_arg, result); + return NULL; + } + result->size = size; + result->size_prime_index = size_prime_index; + result->hash_f = hash_f; + result->eq_f = eq_f; + result->del_f = del_f; + result->alloc_arg = alloc_arg; + result->alloc_with_arg_f = alloc_f; + result->free_with_arg_f = free_f; + return result; +} + +/* + +@deftypefn Supplemental htab_t htab_create_typed_alloc (size_t @var{size}, @ +htab_hash @var{hash_f}, htab_eq @var{eq_f}, htab_del @var{del_f}, @ +htab_alloc @var{alloc_tab_f}, htab_alloc @var{alloc_f}, @ +htab_free @var{free_f}) + +This function creates a hash table that uses two different allocators +@var{alloc_tab_f} and @var{alloc_f} to use for allocating the table itself +and its entries respectively. This is useful when variables of different +types need to be allocated with different allocators. + +The created hash table is slightly larger than @var{size} and it is +initially empty (all the hash table entries are @code{HTAB_EMPTY_ENTRY}). +The function returns the created hash table, or @code{NULL} if memory +allocation fails. + +@end deftypefn + +*/ + +htab_t +htab_create_typed_alloc (size_t size, htab_hash hash_f, htab_eq eq_f, + htab_del del_f, htab_alloc alloc_tab_f, + htab_alloc alloc_f, htab_free free_f) +{ + htab_t result; + unsigned int size_prime_index; + + size_prime_index = higher_prime_index (size); + size = prime_tab[size_prime_index].prime; + + result = (htab_t) (*alloc_tab_f) (1, sizeof (struct htab)); + if (result == NULL) + return NULL; + result->entries = (PTR *) (*alloc_f) (size, sizeof (PTR)); + if (result->entries == NULL) + { + if (free_f != NULL) + (*free_f) (result); + return NULL; + } + result->size = size; + result->size_prime_index = size_prime_index; + result->hash_f = hash_f; + result->eq_f = eq_f; + result->del_f = del_f; + result->alloc_f = alloc_f; + result->free_f = free_f; + return result; +} + + +/* Update the function pointers and allocation parameter in the htab_t. */ + +void +htab_set_functions_ex (htab_t htab, htab_hash hash_f, htab_eq eq_f, + htab_del del_f, PTR alloc_arg, + htab_alloc_with_arg alloc_f, htab_free_with_arg free_f) +{ + htab->hash_f = hash_f; + htab->eq_f = eq_f; + htab->del_f = del_f; + htab->alloc_arg = alloc_arg; + htab->alloc_with_arg_f = alloc_f; + htab->free_with_arg_f = free_f; +} + +/* These functions exist solely for backward compatibility. */ + +#undef htab_create +htab_t +htab_create (size_t size, htab_hash hash_f, htab_eq eq_f, htab_del del_f) +{ + return htab_create_alloc (size, hash_f, eq_f, del_f, xcalloc, free); +} + +htab_t +htab_try_create (size_t size, htab_hash hash_f, htab_eq eq_f, htab_del del_f) +{ + return htab_create_alloc (size, hash_f, eq_f, del_f, calloc, free); +} + +/* This function frees all memory allocated for given hash table. + Naturally the hash table must already exist. */ + +void +htab_delete (htab_t htab) +{ + size_t size = htab_size (htab); + PTR *entries = htab->entries; + int i; + + if (htab->del_f) + for (i = size - 1; i >= 0; i--) + if (entries[i] != HTAB_EMPTY_ENTRY && entries[i] != HTAB_DELETED_ENTRY) + (*htab->del_f) (entries[i]); + + if (htab->free_f != NULL) + { + (*htab->free_f) (entries); + (*htab->free_f) (htab); + } + else if (htab->free_with_arg_f != NULL) + { + (*htab->free_with_arg_f) (htab->alloc_arg, entries); + (*htab->free_with_arg_f) (htab->alloc_arg, htab); + } +} + +/* This function clears all entries in the given hash table. */ + +void +htab_empty (htab_t htab) +{ + size_t size = htab_size (htab); + PTR *entries = htab->entries; + int i; + + if (htab->del_f) + for (i = size - 1; i >= 0; i--) + if (entries[i] != HTAB_EMPTY_ENTRY && entries[i] != HTAB_DELETED_ENTRY) + (*htab->del_f) (entries[i]); + + /* Instead of clearing megabyte, downsize the table. */ + if (size > 1024*1024 / sizeof (PTR)) + { + int nindex = higher_prime_index (1024 / sizeof (PTR)); + int nsize = prime_tab[nindex].prime; + + if (htab->free_f != NULL) + (*htab->free_f) (htab->entries); + else if (htab->free_with_arg_f != NULL) + (*htab->free_with_arg_f) (htab->alloc_arg, htab->entries); + if (htab->alloc_with_arg_f != NULL) + htab->entries = (PTR *) (*htab->alloc_with_arg_f) (htab->alloc_arg, nsize, + sizeof (PTR *)); + else + htab->entries = (PTR *) (*htab->alloc_f) (nsize, sizeof (PTR *)); + htab->size = nsize; + htab->size_prime_index = nindex; + } + else + memset (entries, 0, size * sizeof (PTR)); + htab->n_deleted = 0; + htab->n_elements = 0; +} + +/* Similar to htab_find_slot, but without several unwanted side effects: + - Does not call htab->eq_f when it finds an existing entry. + - Does not change the count of elements/searches/collisions in the + hash table. + This function also assumes there are no deleted entries in the table. + HASH is the hash value for the element to be inserted. */ + +static PTR * +find_empty_slot_for_expand (htab_t htab, hashval_t hash) +{ + hashval_t index = htab_mod (hash, htab); + size_t size = htab_size (htab); + PTR *slot = htab->entries + index; + hashval_t hash2; + + if (*slot == HTAB_EMPTY_ENTRY) + return slot; + else if (*slot == HTAB_DELETED_ENTRY) + abort (); + + hash2 = htab_mod_m2 (hash, htab); + for (;;) + { + index += hash2; + if (index >= size) + index -= size; + + slot = htab->entries + index; + if (*slot == HTAB_EMPTY_ENTRY) + return slot; + else if (*slot == HTAB_DELETED_ENTRY) + abort (); + } +} + +/* The following function changes size of memory allocated for the + entries and repeatedly inserts the table elements. The occupancy + of the table after the call will be about 50%. Naturally the hash + table must already exist. Remember also that the place of the + table entries is changed. If memory allocation failures are allowed, + this function will return zero, indicating that the table could not be + expanded. If all goes well, it will return a non-zero value. */ + +static int +htab_expand (htab_t htab) +{ + PTR *oentries; + PTR *olimit; + PTR *p; + PTR *nentries; + size_t nsize, osize, elts; + unsigned int oindex, nindex; + + oentries = htab->entries; + oindex = htab->size_prime_index; + osize = htab->size; + olimit = oentries + osize; + elts = htab_elements (htab); + + /* Resize only when table after removal of unused elements is either + too full or too empty. */ + if (elts * 2 > osize || (elts * 8 < osize && osize > 32)) + { + nindex = higher_prime_index (elts * 2); + nsize = prime_tab[nindex].prime; + } + else + { + nindex = oindex; + nsize = osize; + } + + if (htab->alloc_with_arg_f != NULL) + nentries = (PTR *) (*htab->alloc_with_arg_f) (htab->alloc_arg, nsize, + sizeof (PTR *)); + else + nentries = (PTR *) (*htab->alloc_f) (nsize, sizeof (PTR *)); + if (nentries == NULL) + return 0; + htab->entries = nentries; + htab->size = nsize; + htab->size_prime_index = nindex; + htab->n_elements -= htab->n_deleted; + htab->n_deleted = 0; + + p = oentries; + do + { + PTR x = *p; + + if (x != HTAB_EMPTY_ENTRY && x != HTAB_DELETED_ENTRY) + { + PTR *q = find_empty_slot_for_expand (htab, (*htab->hash_f) (x)); + + *q = x; + } + + p++; + } + while (p < olimit); + + if (htab->free_f != NULL) + (*htab->free_f) (oentries); + else if (htab->free_with_arg_f != NULL) + (*htab->free_with_arg_f) (htab->alloc_arg, oentries); + return 1; +} + +/* This function searches for a hash table entry equal to the given + element. It cannot be used to insert or delete an element. */ + +PTR +htab_find_with_hash (htab_t htab, const PTR element, hashval_t hash) +{ + hashval_t index, hash2; + size_t size; + PTR entry; + + htab->searches++; + size = htab_size (htab); + index = htab_mod (hash, htab); + + entry = htab->entries[index]; + if (entry == HTAB_EMPTY_ENTRY + || (entry != HTAB_DELETED_ENTRY && (*htab->eq_f) (entry, element))) + return entry; + + hash2 = htab_mod_m2 (hash, htab); + for (;;) + { + htab->collisions++; + index += hash2; + if (index >= size) + index -= size; + + entry = htab->entries[index]; + if (entry == HTAB_EMPTY_ENTRY + || (entry != HTAB_DELETED_ENTRY && (*htab->eq_f) (entry, element))) + return entry; + } +} + +/* Like htab_find_slot_with_hash, but compute the hash value from the + element. */ + +PTR +htab_find (htab_t htab, const PTR element) +{ + return htab_find_with_hash (htab, element, (*htab->hash_f) (element)); +} + +/* This function searches for a hash table slot containing an entry + equal to the given element. To delete an entry, call this with + insert=NO_INSERT, then call htab_clear_slot on the slot returned + (possibly after doing some checks). To insert an entry, call this + with insert=INSERT, then write the value you want into the returned + slot. When inserting an entry, NULL may be returned if memory + allocation fails. */ + +PTR * +htab_find_slot_with_hash (htab_t htab, const PTR element, + hashval_t hash, enum insert_option insert) +{ + PTR *first_deleted_slot; + hashval_t index, hash2; + size_t size; + PTR entry; + + size = htab_size (htab); + if (insert == INSERT && size * 3 <= htab->n_elements * 4) + { + if (htab_expand (htab) == 0) + return NULL; + size = htab_size (htab); + } + + index = htab_mod (hash, htab); + + htab->searches++; + first_deleted_slot = NULL; + + entry = htab->entries[index]; + if (entry == HTAB_EMPTY_ENTRY) + goto empty_entry; + else if (entry == HTAB_DELETED_ENTRY) + first_deleted_slot = &htab->entries[index]; + else if ((*htab->eq_f) (entry, element)) + return &htab->entries[index]; + + hash2 = htab_mod_m2 (hash, htab); + for (;;) + { + htab->collisions++; + index += hash2; + if (index >= size) + index -= size; + + entry = htab->entries[index]; + if (entry == HTAB_EMPTY_ENTRY) + goto empty_entry; + else if (entry == HTAB_DELETED_ENTRY) + { + if (!first_deleted_slot) + first_deleted_slot = &htab->entries[index]; + } + else if ((*htab->eq_f) (entry, element)) + return &htab->entries[index]; + } + + empty_entry: + if (insert == NO_INSERT) + return NULL; + + if (first_deleted_slot) + { + htab->n_deleted--; + *first_deleted_slot = HTAB_EMPTY_ENTRY; + return first_deleted_slot; + } + + htab->n_elements++; + return &htab->entries[index]; +} + +/* Like htab_find_slot_with_hash, but compute the hash value from the + element. */ + +PTR * +htab_find_slot (htab_t htab, const PTR element, enum insert_option insert) +{ + return htab_find_slot_with_hash (htab, element, (*htab->hash_f) (element), + insert); +} + +/* This function deletes an element with the given value from hash + table (the hash is computed from the element). If there is no matching + element in the hash table, this function does nothing. */ + +void +htab_remove_elt (htab_t htab, PTR element) +{ + htab_remove_elt_with_hash (htab, element, (*htab->hash_f) (element)); +} + + +/* This function deletes an element with the given value from hash + table. If there is no matching element in the hash table, this + function does nothing. */ + +void +htab_remove_elt_with_hash (htab_t htab, PTR element, hashval_t hash) +{ + PTR *slot; + + slot = htab_find_slot_with_hash (htab, element, hash, NO_INSERT); + if (*slot == HTAB_EMPTY_ENTRY) + return; + + if (htab->del_f) + (*htab->del_f) (*slot); + + *slot = HTAB_DELETED_ENTRY; + htab->n_deleted++; +} + +/* This function clears a specified slot in a hash table. It is + useful when you've already done the lookup and don't want to do it + again. */ + +void +htab_clear_slot (htab_t htab, PTR *slot) +{ + if (slot < htab->entries || slot >= htab->entries + htab_size (htab) + || *slot == HTAB_EMPTY_ENTRY || *slot == HTAB_DELETED_ENTRY) + abort (); + + if (htab->del_f) + (*htab->del_f) (*slot); + + *slot = HTAB_DELETED_ENTRY; + htab->n_deleted++; +} + +/* This function scans over the entire hash table calling + CALLBACK for each live entry. If CALLBACK returns false, + the iteration stops. INFO is passed as CALLBACK's second + argument. */ + +void +htab_traverse_noresize (htab_t htab, htab_trav callback, PTR info) +{ + PTR *slot; + PTR *limit; + + slot = htab->entries; + limit = slot + htab_size (htab); + + do + { + PTR x = *slot; + + if (x != HTAB_EMPTY_ENTRY && x != HTAB_DELETED_ENTRY) + if (!(*callback) (slot, info)) + break; + } + while (++slot < limit); +} + +/* Like htab_traverse_noresize, but does resize the table when it is + too empty to improve effectivity of subsequent calls. */ + +void +htab_traverse (htab_t htab, htab_trav callback, PTR info) +{ + size_t size = htab_size (htab); + if (htab_elements (htab) * 8 < size && size > 32) + htab_expand (htab); + + htab_traverse_noresize (htab, callback, info); +} + +/* Return the fraction of fixed collisions during all work with given + hash table. */ + +double +htab_collisions (htab_t htab) +{ + if (htab->searches == 0) + return 0.0; + + return (double) htab->collisions / (double) htab->searches; +} + +/* Hash P as a null-terminated string. + + Copied from gcc/hashtable.c. Zack had the following to say with respect + to applicability, though note that unlike hashtable.c, this hash table + implementation re-hashes rather than chain buckets. + + http://gcc.gnu.org/ml/gcc-patches/2001-08/msg01021.html + From: Zack Weinberg <zackw@panix.com> + Date: Fri, 17 Aug 2001 02:15:56 -0400 + + I got it by extracting all the identifiers from all the source code + I had lying around in mid-1999, and testing many recurrences of + the form "H_n = H_{n-1} * K + c_n * L + M" where K, L, M were either + prime numbers or the appropriate identity. This was the best one. + I don't remember exactly what constituted "best", except I was + looking at bucket-length distributions mostly. + + So it should be very good at hashing identifiers, but might not be + as good at arbitrary strings. + + I'll add that it thoroughly trounces the hash functions recommended + for this use at http://burtleburtle.net/bob/hash/index.html, both + on speed and bucket distribution. I haven't tried it against the + function they just started using for Perl's hashes. */ + +hashval_t +htab_hash_string (const PTR p) +{ + const unsigned char *str = (const unsigned char *) p; + hashval_t r = 0; + unsigned char c; + + while ((c = *str++) != 0) + r = r * 67 + c - 113; + + return r; +} + +/* DERIVED FROM: +-------------------------------------------------------------------- +lookup2.c, by Bob Jenkins, December 1996, Public Domain. +hash(), hash2(), hash3, and mix() are externally useful functions. +Routines to test the hash are included if SELF_TEST is defined. +You can use this free for any purpose. It has no warranty. +-------------------------------------------------------------------- +*/ + +/* +-------------------------------------------------------------------- +mix -- mix 3 32-bit values reversibly. +For every delta with one or two bit set, and the deltas of all three + high bits or all three low bits, whether the original value of a,b,c + is almost all zero or is uniformly distributed, +* If mix() is run forward or backward, at least 32 bits in a,b,c + have at least 1/4 probability of changing. +* If mix() is run forward, every bit of c will change between 1/3 and + 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.) +mix() was built out of 36 single-cycle latency instructions in a + structure that could supported 2x parallelism, like so: + a -= b; + a -= c; x = (c>>13); + b -= c; a ^= x; + b -= a; x = (a<<8); + c -= a; b ^= x; + c -= b; x = (b>>13); + ... + Unfortunately, superscalar Pentiums and Sparcs can't take advantage + of that parallelism. They've also turned some of those single-cycle + latency instructions into multi-cycle latency instructions. Still, + this is the fastest good hash I could find. There were about 2^^68 + to choose from. I only looked at a billion or so. +-------------------------------------------------------------------- +*/ +/* same, but slower, works on systems that might have 8 byte hashval_t's */ +#define mix(a,b,c) \ +{ \ + a -= b; a -= c; a ^= (c>>13); \ + b -= c; b -= a; b ^= (a<< 8); \ + c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \ + a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \ + b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \ + c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \ + a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \ + b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \ + c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \ +} + +/* +-------------------------------------------------------------------- +hash() -- hash a variable-length key into a 32-bit value + k : the key (the unaligned variable-length array of bytes) + len : the length of the key, counting by bytes + level : can be any 4-byte value +Returns a 32-bit value. Every bit of the key affects every bit of +the return value. Every 1-bit and 2-bit delta achieves avalanche. +About 36+6len instructions. + +The best hash table sizes are powers of 2. There is no need to do +mod a prime (mod is sooo slow!). If you need less than 32 bits, +use a bitmask. For example, if you need only 10 bits, do + h = (h & hashmask(10)); +In which case, the hash table should have hashsize(10) elements. + +If you are hashing n strings (ub1 **)k, do it like this: + for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h); + +By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this +code any way you wish, private, educational, or commercial. It's free. + +See http://burtleburtle.net/bob/hash/evahash.html +Use for hash table lookup, or anything where one collision in 2^32 is +acceptable. Do NOT use for cryptographic purposes. +-------------------------------------------------------------------- +*/ + +hashval_t +iterative_hash (const PTR k_in /* the key */, + register size_t length /* the length of the key */, + register hashval_t initval /* the previous hash, or + an arbitrary value */) +{ + register const unsigned char *k = (const unsigned char *)k_in; + register hashval_t a,b,c,len; + + /* Set up the internal state */ + len = length; + a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */ + c = initval; /* the previous hash value */ + + /*---------------------------------------- handle most of the key */ +#ifndef WORDS_BIGENDIAN + /* On a little-endian machine, if the data is 4-byte aligned we can hash + by word for better speed. This gives nondeterministic results on + big-endian machines. */ + if (sizeof (hashval_t) == 4 && (((size_t)k)&3) == 0) + while (len >= 12) /* aligned */ + { + a += *(hashval_t *)(k+0); + b += *(hashval_t *)(k+4); + c += *(hashval_t *)(k+8); + mix(a,b,c); + k += 12; len -= 12; + } + else /* unaligned */ +#endif + while (len >= 12) + { + a += (k[0] +((hashval_t)k[1]<<8) +((hashval_t)k[2]<<16) +((hashval_t)k[3]<<24)); + b += (k[4] +((hashval_t)k[5]<<8) +((hashval_t)k[6]<<16) +((hashval_t)k[7]<<24)); + c += (k[8] +((hashval_t)k[9]<<8) +((hashval_t)k[10]<<16)+((hashval_t)k[11]<<24)); + mix(a,b,c); + k += 12; len -= 12; + } + + /*------------------------------------- handle the last 11 bytes */ + c += length; + switch(len) /* all the case statements fall through */ + { + case 11: c+=((hashval_t)k[10]<<24); + case 10: c+=((hashval_t)k[9]<<16); + case 9 : c+=((hashval_t)k[8]<<8); + /* the first byte of c is reserved for the length */ + case 8 : b+=((hashval_t)k[7]<<24); + case 7 : b+=((hashval_t)k[6]<<16); + case 6 : b+=((hashval_t)k[5]<<8); + case 5 : b+=k[4]; + case 4 : a+=((hashval_t)k[3]<<24); + case 3 : a+=((hashval_t)k[2]<<16); + case 2 : a+=((hashval_t)k[1]<<8); + case 1 : a+=k[0]; + /* case 0: nothing left to add */ + } + mix(a,b,c); + /*-------------------------------------------- report the result */ + return c; +} |