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 <errno.h> 27 #include <limits.h> 28 #include <search.h> 29 #include <stdint.h> 30 #include <stdlib.h> 31 #include <string.h> 32 33 #include "hsearch.h" 34 35 /* 36 * Look up an unused entry in the hash table for a given hash. For this 37 * implementation we use quadratic probing. Quadratic probing has the 38 * advantage of preventing primary clustering. 39 */ 40 static ENTRY * 41 hsearch_lookup_free(struct __hsearch *hsearch, size_t hash) 42 { 43 size_t index, i; 44 45 for (index = hash, i = 0;; index += ++i) { 46 ENTRY *entry = &hsearch->entries[index & hsearch->index_mask]; 47 if (entry->key == NULL) 48 return (entry); 49 } 50 } 51 52 /* 53 * Computes an FNV-1a hash of the key. Depending on the pointer size, this 54 * either uses the 32- or 64-bit FNV prime. 55 */ 56 static size_t 57 hsearch_hash(size_t offset_basis, const char *str) 58 { 59 size_t hash; 60 61 hash = offset_basis; 62 while (*str != '\0') { 63 hash ^= (uint8_t)*str++; 64 if (sizeof(size_t) * CHAR_BIT <= 32) 65 hash *= UINT32_C(16777619); 66 else 67 hash *= UINT64_C(1099511628211); 68 } 69 return (hash); 70 } 71 72 int 73 hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab) 74 { 75 struct __hsearch *hsearch; 76 ENTRY *entry, *old_entries, *new_entries; 77 size_t hash, index, i, old_hash, old_count, new_count; 78 79 hsearch = htab->__hsearch; 80 hash = hsearch_hash(hsearch->offset_basis, item.key); 81 82 /* 83 * Search the hash table for an existing entry for this key. 84 * Stop searching if we run into an unused hash table entry. 85 */ 86 for (index = hash, i = 0;; index += ++i) { 87 entry = &hsearch->entries[index & hsearch->index_mask]; 88 if (entry->key == NULL) 89 break; 90 if (strcmp(entry->key, item.key) == 0) { 91 *retval = entry; 92 return (1); 93 } 94 } 95 96 /* Only perform the insertion if action is set to ENTER. */ 97 if (action == FIND) { 98 errno = ESRCH; 99 return (0); 100 } 101 102 if (hsearch->entries_used * 2 >= hsearch->index_mask) { 103 /* Preserve the old hash table entries. */ 104 old_count = hsearch->index_mask + 1; 105 old_entries = hsearch->entries; 106 107 /* 108 * Allocate and install a new table if insertion would 109 * yield a hash table that is more than 50% used. By 110 * using 50% as a threshold, a lookup will only take up 111 * to two steps on average. 112 */ 113 new_count = (hsearch->index_mask + 1) * 2; 114 new_entries = calloc(new_count, sizeof(ENTRY)); 115 if (new_entries == NULL) 116 return (0); 117 hsearch->entries = new_entries; 118 hsearch->index_mask = new_count - 1; 119 120 /* Copy over the entries from the old table to the new table. */ 121 for (i = 0; i < old_count; ++i) { 122 entry = &old_entries[i]; 123 if (entry->key != NULL) { 124 old_hash = hsearch_hash(hsearch->offset_basis, 125 entry->key); 126 *hsearch_lookup_free(hsearch, old_hash) = 127 *entry; 128 } 129 } 130 131 /* Destroy the old hash table entries. */ 132 free(old_entries); 133 134 /* 135 * Perform a new lookup for a free table entry, so that 136 * we insert the entry into the new hash table. 137 */ 138 hsearch = htab->__hsearch; 139 entry = hsearch_lookup_free(hsearch, hash); 140 } 141 142 /* Insert the new entry into the hash table. */ 143 *entry = item; 144 ++hsearch->entries_used; 145 *retval = entry; 146 return (1); 147 } 148