src/str_pool.c

   1 /* ncmpc (Ncurses MPD Client)
   2  * (c) 2004-2010 The Music Player Daemon Project
   3  * Project homepage: http://musicpd.org
   4
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #include "str_pool.h"
  21
  22 #include <assert.h>
  23 #include <stddef.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26
  27 #define NUM_SLOTS 4096
  28
  29 struct slot {
  30         struct slot *next;
  31         unsigned char ref;
  32         char value[1];
  33 } __attribute__((packed));
  34
  35 static struct slot *slots[NUM_SLOTS];
  36
  37 static inline unsigned
  38 calc_hash(const char *p)
  39 {
  40         unsigned hash = 5381;
  41
  42         assert(p != NULL);
  43
  44         while (*p != 0)
  45                 hash = (hash << 5) + hash + *p++;
  46
  47         return hash;
  48 }
  49
  50 static inline struct slot *
  51 value_to_slot(char *value)
  52 {
  53         return (struct slot*)(value - offsetof(struct slot, value));
  54 }
  55
  56 static struct slot *slot_alloc(struct slot *next, const char *value)
  57 {
  58         size_t length = strlen(value);
  59         struct slot *slot = malloc(sizeof(*slot) + length);
  60         if (slot == NULL)
  61                 abort(); /* XXX */
  62
  63         slot->next = next;
  64         slot->ref = 1;
  65         memcpy(slot->value, value, length + 1);
  66         return slot;
  67 }
  68
  69 char *str_pool_get(const char *value)
  70 {
  71         struct slot **slot_p, *slot;
  72
  73         slot_p = &slots[calc_hash(value) % NUM_SLOTS];
  74         for (slot = *slot_p; slot != NULL; slot = slot->next) {
  75                 if (strcmp(value, slot->value) == 0 && slot->ref < 0xff) {
  76                         assert(slot->ref > 0);
  77                         ++slot->ref;
  78                         return slot->value;
  79                 }
  80         }
  81
  82         slot = slot_alloc(*slot_p, value);
  83         *slot_p = slot;
  84         return slot->value;
  85 }
  86
  87 char *str_pool_dup(char *value)
  88 {
  89         struct slot *slot = value_to_slot(value);
  90
  91         assert(slot->ref > 0);
  92
  93         if (slot->ref < 0xff) {
  94                 ++slot->ref;
  95                 return value;
  96         } else {
  97                 /* the reference counter overflows above 0xff;
  98                    duplicate the value, and start with 1 */
  99                 struct slot **slot_p =
 100                         &slots[calc_hash(slot->value) % NUM_SLOTS];
 101                 slot = slot_alloc(*slot_p, slot->value);
 102                 *slot_p = slot;
 103                 return slot->value;
 104         }
 105 }
 106
 107 void str_pool_put(char *value)
 108 {
 109         struct slot **slot_p, *slot;
 110
 111         slot = value_to_slot(value);
 112         assert(slot->ref > 0);
 113         --slot->ref;
 114
 115         if (slot->ref > 0)
 116                 return;
 117
 118         for (slot_p = &slots[calc_hash(value) % NUM_SLOTS];
 119              *slot_p != slot;
 120              slot_p = &(*slot_p)->next) {
 121                 assert(*slot_p != NULL);
 122         }
 123
 124         *slot_p = slot->next;
 125         free(slot);
 126 }