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Sourcecode: ncmpcpp version File versions

str_pool.c

/* ncmpc
 * Copyright (C) 2008 Max Kellermann <max@duempel.org>
 * This project's homepage is: http://www.musicpd.org
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include "str_pool.h"

//#include <assert.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#define NUM_SLOTS 4096

struct slot {
      struct slot *next;
      unsigned char ref;
      char value[1];
} __attribute__((packed));

struct slot *slots[NUM_SLOTS];

static inline unsigned
calc_hash(const char *p)
{
      unsigned hash = 5381;

      //assert(p != NULL);

      while (*p != 0)
            hash = (hash << 5) + hash + *p++;

      return hash;
}

static inline struct slot *
value_to_slot(const char *value)
{
      return (struct slot*)(value - offsetof(struct slot, value));
}

static struct slot *slot_alloc(struct slot *next, const char *value)
{
      size_t length = strlen(value);
      struct slot *slot = malloc(sizeof(*slot) + length);
      if (slot == NULL)
            abort(); /* XXX */

      slot->next = next;
      slot->ref = 1;
      memcpy(slot->value, value, length + 1);
      return slot;
}

char *str_pool_get(const char *value)
{
      struct slot **slot_p, *slot;

      slot_p = &slots[calc_hash(value) % NUM_SLOTS];
      for (slot = *slot_p; slot != NULL; slot = slot->next) {
            if (strcmp(value, slot->value) == 0 && slot->ref < 0xff) {
                  //assert(slot->ref > 0);
                  ++slot->ref;
                  return slot->value;
            }
      }

      slot = slot_alloc(*slot_p, value);
      *slot_p = slot;
      return slot->value;
}

char *str_pool_dup(const char *value)
{
      struct slot *slot = value_to_slot(value);

      //assert(slot->ref > 0);

      if (slot->ref < 0xff) {
            ++slot->ref;
            return (char *) value;
      } else {
            /* the reference counter overflows above 0xff;
               duplicate the value, and start with 1 */
            struct slot **slot_p =
                  &slots[calc_hash(slot->value) % NUM_SLOTS];
            slot = slot_alloc(*slot_p, slot->value);
            *slot_p = slot;
            return slot->value;
      }
}

void str_pool_put(char *value)
{
      struct slot **slot_p, *slot;

      slot = value_to_slot(value);
      //assert(slot->ref > 0);
      --slot->ref;

      if (slot->ref > 0)
            return;

      for (slot_p = &slots[calc_hash(value) % NUM_SLOTS];
           *slot_p != slot;
           slot_p = &(*slot_p)->next) {
            //assert(*slot_p != NULL);
      }

      *slot_p = slot->next;
      free(slot);
}

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