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      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: head/lib/libc/stdlib/hsearch_r.c 292767 2015-12-27 07:50:11Z ed $");
     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