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Diffstat (limited to 'src/TagPool.cxx')
-rw-r--r-- | src/TagPool.cxx | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/src/TagPool.cxx b/src/TagPool.cxx new file mode 100644 index 000000000..f529cda69 --- /dev/null +++ b/src/TagPool.cxx @@ -0,0 +1,149 @@ +/* + * Copyright (C) 2003-2013 The Music Player Daemon Project + * 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 Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +#include "config.h" +#include "TagPool.hxx" + +#include <assert.h> + +Mutex tag_pool_lock; + +#define NUM_SLOTS 4096 + +struct slot { + struct slot *next; + unsigned char ref; + struct tag_item item; +} mpd_packed; + +static struct slot *slots[NUM_SLOTS]; + +static inline unsigned +calc_hash_n(enum tag_type type, const char *p, size_t length) +{ + unsigned hash = 5381; + + assert(p != nullptr); + + while (length-- > 0) + hash = (hash << 5) + hash + *p++; + + return hash ^ type; +} + +static inline unsigned +calc_hash(enum tag_type type, const char *p) +{ + unsigned hash = 5381; + + assert(p != nullptr); + + while (*p != 0) + hash = (hash << 5) + hash + *p++; + + return hash ^ type; +} + +static inline struct slot * +tag_item_to_slot(struct tag_item *item) +{ + return (struct slot*)(((char*)item) - offsetof(struct slot, item)); +} + +static struct slot *slot_alloc(struct slot *next, + enum tag_type type, + const char *value, int length) +{ + struct slot *slot; + + slot = (struct slot *) + g_malloc(sizeof(*slot) - sizeof(slot->item.value) + length + 1); + slot->next = next; + slot->ref = 1; + slot->item.type = type; + memcpy(slot->item.value, value, length); + slot->item.value[length] = 0; + return slot; +} + +struct tag_item * +tag_pool_get_item(enum tag_type type, const char *value, size_t length) +{ + struct slot **slot_p, *slot; + + slot_p = &slots[calc_hash_n(type, value, length) % NUM_SLOTS]; + for (slot = *slot_p; slot != nullptr; slot = slot->next) { + if (slot->item.type == type && + length == strlen(slot->item.value) && + memcmp(value, slot->item.value, length) == 0 && + slot->ref < 0xff) { + assert(slot->ref > 0); + ++slot->ref; + return &slot->item; + } + } + + slot = slot_alloc(*slot_p, type, value, length); + *slot_p = slot; + return &slot->item; +} + +struct tag_item *tag_pool_dup_item(struct tag_item *item) +{ + struct slot *slot = tag_item_to_slot(item); + + assert(slot->ref > 0); + + if (slot->ref < 0xff) { + ++slot->ref; + return item; + } else { + /* the reference counter overflows above 0xff; + duplicate the item, and start with 1 */ + size_t length = strlen(item->value); + struct slot **slot_p = + &slots[calc_hash_n(item->type, item->value, + length) % NUM_SLOTS]; + slot = slot_alloc(*slot_p, item->type, + item->value, strlen(item->value)); + *slot_p = slot; + return &slot->item; + } +} + +void tag_pool_put_item(struct tag_item *item) +{ + struct slot **slot_p, *slot; + + slot = tag_item_to_slot(item); + assert(slot->ref > 0); + --slot->ref; + + if (slot->ref > 0) + return; + + for (slot_p = &slots[calc_hash(item->type, item->value) % NUM_SLOTS]; + *slot_p != slot; + slot_p = &(*slot_p)->next) { + assert(*slot_p != nullptr); + } + + *slot_p = slot->next; + g_free(slot); +} |