root/hashmap.c

DEFINITIONS

1. strhash
2. strihash
3. memhash
4. memihash
5. alloc_table
6. entry_equals
7. bucket
8. rehash
9. find_entry_ptr
10. always_equal
11. hashmap_init
12. hashmap_free
13. hashmap_get
14. hashmap_get_next
15. hashmap_add
16. hashmap_remove
17. hashmap_put
18. hashmap_iter_init
19. hashmap_iter_next
20. pool_entry_cmp
21. memintern

/*
 * Generic implementation of hash-based key value mappings.
 */
#include "cache.h"
#include "hashmap.h"

#define FNV32_BASE ((unsigned int) 0x811c9dc5)
#define FNV32_PRIME ((unsigned int) 0x01000193)

unsigned int strhash(const char *str)
{
        unsigned int c, hash = FNV32_BASE;
        while ((c = (unsigned char) *str++))
                hash = (hash * FNV32_PRIME) ^ c;
        return hash;
}

unsigned int strihash(const char *str)
{
        unsigned int c, hash = FNV32_BASE;
        while ((c = (unsigned char) *str++)) {
                if (c >= 'a' && c <= 'z')
                        c -= 'a' - 'A';
                hash = (hash * FNV32_PRIME) ^ c;
        }
        return hash;
}

unsigned int memhash(const void *buf, size_t len)
{
        unsigned int hash = FNV32_BASE;
        unsigned char *ucbuf = (unsigned char *) buf;
        while (len--) {
                unsigned int c = *ucbuf++;
                hash = (hash * FNV32_PRIME) ^ c;
        }
        return hash;
}

unsigned int memihash(const void *buf, size_t len)
{
        unsigned int hash = FNV32_BASE;
        unsigned char *ucbuf = (unsigned char *) buf;
        while (len--) {
                unsigned int c = *ucbuf++;
                if (c >= 'a' && c <= 'z')
                        c -= 'a' - 'A';
                hash = (hash * FNV32_PRIME) ^ c;
        }
        return hash;
}

#define HASHMAP_INITIAL_SIZE 64
/* grow / shrink by 2^2 */
#define HASHMAP_RESIZE_BITS 2
/* load factor in percent */
#define HASHMAP_LOAD_FACTOR 80

static void alloc_table(struct hashmap *map, unsigned int size)
{
        map->tablesize = size;
        map->table = xcalloc(size, sizeof(struct hashmap_entry *));

        /* calculate resize thresholds for new size */
        map->grow_at = (unsigned int) ((uint64_t) size * HASHMAP_LOAD_FACTOR / 100);
        if (size <= HASHMAP_INITIAL_SIZE)
                map->shrink_at = 0;
        else
                /*
                 * The shrink-threshold must be slightly smaller than
                 * (grow-threshold / resize-factor) to prevent erratic resizing,
                 * thus we divide by (resize-factor + 1).
                 */
                map->shrink_at = map->grow_at / ((1 << HASHMAP_RESIZE_BITS) + 1);
}

static inline int entry_equals(const struct hashmap *map,
                const struct hashmap_entry *e1, const struct hashmap_entry *e2,
                const void *keydata)
{
        return (e1 == e2) || (e1->hash == e2->hash && !map->cmpfn(e1, e2, keydata));
}

static inline unsigned int bucket(const struct hashmap *map,
                const struct hashmap_entry *key)
{
        return key->hash & (map->tablesize - 1);
}

static void rehash(struct hashmap *map, unsigned int newsize)
{
        unsigned int i, oldsize = map->tablesize;
        struct hashmap_entry **oldtable = map->table;

        alloc_table(map, newsize);
        for (i = 0; i < oldsize; i++) {
                struct hashmap_entry *e = oldtable[i];
                while (e) {
                        struct hashmap_entry *next = e->next;
                        unsigned int b = bucket(map, e);
                        e->next = map->table[b];
                        map->table[b] = e;
                        e = next;
                }
        }
        free(oldtable);
}

static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
                const struct hashmap_entry *key, const void *keydata)
{
        struct hashmap_entry **e = &map->table[bucket(map, key)];
        while (*e && !entry_equals(map, *e, key, keydata))
                e = &(*e)->next;
        return e;
}

static int always_equal(const void *unused1, const void *unused2, const void *unused3)
{
        return 0;
}

void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
                size_t initial_size)
{
        unsigned int size = HASHMAP_INITIAL_SIZE;
        map->size = 0;
        map->cmpfn = equals_function ? equals_function : always_equal;

        /* calculate initial table size and allocate the table */
        initial_size = (unsigned int) ((uint64_t) initial_size * 100
                        / HASHMAP_LOAD_FACTOR);
        while (initial_size > size)
                size <<= HASHMAP_RESIZE_BITS;
        alloc_table(map, size);
}

void hashmap_free(struct hashmap *map, int free_entries)
{
        if (!map || !map->table)
                return;
        if (free_entries) {
                struct hashmap_iter iter;
                struct hashmap_entry *e;
                hashmap_iter_init(map, &iter);
                while ((e = hashmap_iter_next(&iter)))
                        free(e);
        }
        free(map->table);
        memset(map, 0, sizeof(*map));
}

void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)
{
        return *find_entry_ptr(map, key, keydata);
}

void *hashmap_get_next(const struct hashmap *map, const void *entry)
{
        struct hashmap_entry *e = ((struct hashmap_entry *) entry)->next;
        for (; e; e = e->next)
                if (entry_equals(map, entry, e, NULL))
                        return e;
        return NULL;
}

void hashmap_add(struct hashmap *map, void *entry)
{
        unsigned int b = bucket(map, entry);

        /* add entry */
        ((struct hashmap_entry *) entry)->next = map->table[b];
        map->table[b] = entry;

        /* fix size and rehash if appropriate */
        map->size++;
        if (map->size > map->grow_at)
                rehash(map, map->tablesize << HASHMAP_RESIZE_BITS);
}

void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)
{
        struct hashmap_entry *old;
        struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
        if (!*e)
                return NULL;

        /* remove existing entry */
        old = *e;
        *e = old->next;
        old->next = NULL;

        /* fix size and rehash if appropriate */
        map->size--;
        if (map->size < map->shrink_at)
                rehash(map, map->tablesize >> HASHMAP_RESIZE_BITS);
        return old;
}

void *hashmap_put(struct hashmap *map, void *entry)
{
        struct hashmap_entry *old = hashmap_remove(map, entry, NULL);
        hashmap_add(map, entry);
        return old;
}

void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)
{
        iter->map = map;
        iter->tablepos = 0;
        iter->next = NULL;
}

void *hashmap_iter_next(struct hashmap_iter *iter)
{
        struct hashmap_entry *current = iter->next;
        for (;;) {
                if (current) {
                        iter->next = current->next;
                        return current;
                }

                if (iter->tablepos >= iter->map->tablesize)
                        return NULL;

                current = iter->map->table[iter->tablepos++];
        }
}

struct pool_entry {
        struct hashmap_entry ent;
        size_t len;
        unsigned char data[FLEX_ARRAY];
};

static int pool_entry_cmp(const struct pool_entry *e1,
                          const struct pool_entry *e2,
                          const unsigned char *keydata)
{
        return e1->data != keydata &&
               (e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
}

const void *memintern(const void *data, size_t len)
{
        static struct hashmap map;
        struct pool_entry key, *e;

        /* initialize string pool hashmap */
        if (!map.tablesize)
                hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, 0);

        /* lookup interned string in pool */
        hashmap_entry_init(&key, memhash(data, len));
        key.len = len;
        e = hashmap_get(&map, &key, data);
        if (!e) {
                /* not found: create it */
                e = xmallocz(sizeof(struct pool_entry) + len);
                hashmap_entry_init(e, key.ent.hash);
                e->len = len;
                memcpy(e->data, data, len);
                hashmap_add(&map, e);
        }
        return e->data;
}