1 /*- 2 * Copyright (c) 2015 Nuxi, https://nuxi.nl/ 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23 * SUCH DAMAGE. 24 */ 25 26 #include <sys/cdefs.h> 27 __FBSDID("$FreeBSD$"); 28 29 #include <errno.h> 30 #include <limits.h> 31 #include <search.h> 32 #include <stdint.h> 33 #include <stdlib.h> 34 #include <string.h> 35 36 #include "hsearch.h" 37 38 /* 39 * Look up an unused entry in the hash table for a given hash. For this 40 * implementation we use quadratic probing. Quadratic probing has the 41 * advantage of preventing primary clustering. 42 */ 43 static ENTRY * 44 hsearch_lookup_free(struct __hsearch *hsearch, size_t hash) 45 { 46 size_t index, i; 47 48 for (index = hash, i = 0;; index += ++i) { 49 ENTRY *entry = &hsearch->entries[index & hsearch->index_mask]; 50 if (entry->key == NULL) 51 return (entry); 52 } 53 } 54 55 /* 56 * Computes an FNV-1a hash of the key. Depending on the pointer size, this 57 * either uses the 32- or 64-bit FNV prime. 58 */ 59 static size_t 60 hsearch_hash(size_t offset_basis, const char *str) 61 { 62 size_t hash; 63 64 hash = offset_basis; 65 while (*str != '\0') { 66 hash ^= (uint8_t)*str++; 67 if (sizeof(size_t) * CHAR_BIT <= 32) 68 hash *= UINT32_C(16777619); 69 else 70 hash *= UINT64_C(1099511628211); 71 } 72 return (hash); 73 } 74 75 int 76 hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab) 77 { 78 struct __hsearch *hsearch; 79 ENTRY *entry, *old_entries, *new_entries; 80 size_t hash, index, i, old_hash, old_count, new_count; 81 82 hsearch = htab->__hsearch; 83 hash = hsearch_hash(hsearch->offset_basis, item.key); 84 85 /* 86 * Search the hash table for an existing entry for this key. 87 * Stop searching if we run into an unused hash table entry. 88 */ 89 for (index = hash, i = 0;; index += ++i) { 90 entry = &hsearch->entries[index & hsearch->index_mask]; 91 if (entry->key == NULL) 92 break; 93 if (strcmp(entry->key, item.key) == 0) { 94 *retval = entry; 95 return (1); 96 } 97 } 98 99 /* Only perform the insertion if action is set to ENTER. */ 100 if (action == FIND) { 101 errno = ESRCH; 102 return (0); 103 } 104 105 if (hsearch->entries_used * 2 >= hsearch->index_mask) { 106 /* Preserve the old hash table entries. */ 107 old_count = hsearch->index_mask + 1; 108 old_entries = hsearch->entries; 109 110 /* 111 * Allocate and install a new table if insertion would 112 * yield a hash table that is more than 50% used. By 113 * using 50% as a threshold, a lookup will only take up 114 * to two steps on average. 115 */ 116 new_count = (hsearch->index_mask + 1) * 2; 117 new_entries = calloc(new_count, sizeof(ENTRY)); 118 if (new_entries == NULL) 119 return (0); 120 hsearch->entries = new_entries; 121 hsearch->index_mask = new_count - 1; 122 123 /* Copy over the entries from the old table to the new table. */ 124 for (i = 0; i < old_count; ++i) { 125 entry = &old_entries[i]; 126 if (entry->key != NULL) { 127 old_hash = hsearch_hash(hsearch->offset_basis, 128 entry->key); 129 *hsearch_lookup_free(hsearch, old_hash) = 130 *entry; 131 } 132 } 133 134 /* Destroy the old hash table entries. */ 135 free(old_entries); 136 137 /* 138 * Perform a new lookup for a free table entry, so that 139 * we insert the entry into the new hash table. 140 */ 141 hsearch = htab->__hsearch; 142 entry = hsearch_lookup_free(hsearch, hash); 143 } 144 145 /* Insert the new entry into the hash table. */ 146 *entry = item; 147 ++hsearch->entries_used; 148 *retval = entry; 149 return (1); 150 } 151