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 #include <errno.h> 28 #include <limits.h> 29 #include <search.h> 30 #include <stdint.h> 31 #include <stdlib.h> 32 #include <string.h> 33 34 #include "hsearch.h" 35 36 /* 37 * Look up an unused entry in the hash table for a given hash. For this 38 * implementation we use quadratic probing. Quadratic probing has the 39 * advantage of preventing primary clustering. 40 */ 41 static ENTRY * 42 hsearch_lookup_free(struct __hsearch *hsearch, size_t hash) 43 { 44 size_t index, i; 45 46 for (index = hash, i = 0;; index += ++i) { 47 ENTRY *entry = &hsearch->entries[index & hsearch->index_mask]; 48 if (entry->key == NULL) 49 return (entry); 50 } 51 } 52 53 /* 54 * Computes an FNV-1a hash of the key. Depending on the pointer size, this 55 * either uses the 32- or 64-bit FNV prime. 56 */ 57 static size_t 58 hsearch_hash(size_t offset_basis, const char *str) 59 { 60 size_t hash; 61 62 hash = offset_basis; 63 while (*str != '\0') { 64 hash ^= (uint8_t)*str++; 65 if (sizeof(size_t) * CHAR_BIT <= 32) 66 hash *= UINT32_C(16777619); 67 else 68 hash *= UINT64_C(1099511628211); 69 } 70 return (hash); 71 } 72 73 int 74 hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab) 75 { 76 struct __hsearch *hsearch; 77 ENTRY *entry, *old_entries, *new_entries; 78 size_t hash, index, i, old_hash, old_count, new_count; 79 80 hsearch = htab->__hsearch; 81 hash = hsearch_hash(hsearch->offset_basis, item.key); 82 83 /* 84 * Search the hash table for an existing entry for this key. 85 * Stop searching if we run into an unused hash table entry. 86 */ 87 for (index = hash, i = 0;; index += ++i) { 88 entry = &hsearch->entries[index & hsearch->index_mask]; 89 if (entry->key == NULL) 90 break; 91 if (strcmp(entry->key, item.key) == 0) { 92 *retval = entry; 93 return (1); 94 } 95 } 96 97 /* Only perform the insertion if action is set to ENTER. */ 98 if (action == FIND) { 99 errno = ESRCH; 100 return (0); 101 } 102 103 if (hsearch->entries_used * 2 >= hsearch->index_mask) { 104 /* Preserve the old hash table entries. */ 105 old_count = hsearch->index_mask + 1; 106 old_entries = hsearch->entries; 107 108 /* 109 * Allocate and install a new table if insertion would 110 * yield a hash table that is more than 50% used. By 111 * using 50% as a threshold, a lookup will only take up 112 * to two steps on average. 113 */ 114 new_count = (hsearch->index_mask + 1) * 2; 115 new_entries = calloc(new_count, sizeof(ENTRY)); 116 if (new_entries == NULL) 117 return (0); 118 hsearch->entries = new_entries; 119 hsearch->index_mask = new_count - 1; 120 121 /* Copy over the entries from the old table to the new table. */ 122 for (i = 0; i < old_count; ++i) { 123 entry = &old_entries[i]; 124 if (entry->key != NULL) { 125 old_hash = hsearch_hash(hsearch->offset_basis, 126 entry->key); 127 *hsearch_lookup_free(hsearch, old_hash) = 128 *entry; 129 } 130 } 131 132 /* Destroy the old hash table entries. */ 133 free(old_entries); 134 135 /* 136 * Perform a new lookup for a free table entry, so that 137 * we insert the entry into the new hash table. 138 */ 139 hsearch = htab->__hsearch; 140 entry = hsearch_lookup_free(hsearch, hash); 141 } 142 143 /* Insert the new entry into the hash table. */ 144 *entry = item; 145 ++hsearch->entries_used; 146 *retval = entry; 147 return (1); 148 } 149