/*
* Generic implementation of hash-based key-value mappings.
- * See Documentation/technical/api-hashmap.txt.
+ *
+ * An example that maps long to a string:
+ * For the sake of the example this allows to lookup exact values, too
+ * (i.e. it is operated as a set, the value is part of the key)
+ * -------------------------------------
+ *
+ * struct hashmap map;
+ * struct long2string {
+ * struct hashmap_entry ent; // must be the first member!
+ * long key;
+ * char value[FLEX_ARRAY]; // be careful with allocating on stack!
+ * };
+ *
+ * #define COMPARE_VALUE 1
+ *
+ * static int long2string_cmp(const struct long2string *e1,
+ * const struct long2string *e2,
+ * const void *keydata, const void *userdata)
+ * {
+ * char *string = keydata;
+ * unsigned *flags = (unsigned*)userdata;
+ *
+ * if (flags & COMPARE_VALUE)
+ * return !(e1->key == e2->key) || (keydata ?
+ * strcmp(e1->value, keydata) : strcmp(e1->value, e2->value));
+ * else
+ * return !(e1->key == e2->key);
+ * }
+ *
+ * int main(int argc, char **argv)
+ * {
+ * long key;
+ * char *value, *action;
+ *
+ * unsigned flags = ALLOW_DUPLICATE_KEYS;
+ *
+ * hashmap_init(&map, (hashmap_cmp_fn) long2string_cmp, &flags, 0);
+ *
+ * while (scanf("%s %l %s", action, key, value)) {
+ *
+ * if (!strcmp("add", action)) {
+ * struct long2string *e;
+ * e = malloc(sizeof(struct long2string) + strlen(value));
+ * hashmap_entry_init(e, memhash(&key, sizeof(long)));
+ * e->key = key;
+ * memcpy(e->value, value, strlen(value));
+ * hashmap_add(&map, e);
+ * }
+ *
+ * if (!strcmp("print_all_by_key", action)) {
+ * flags &= ~COMPARE_VALUE;
+ *
+ * struct long2string k;
+ * hashmap_entry_init(&k, memhash(&key, sizeof(long)));
+ * k.key = key;
+ *
+ * struct long2string *e = hashmap_get(&map, &k, NULL);
+ * if (e) {
+ * printf("first: %l %s\n", e->key, e->value);
+ * while (e = hashmap_get_next(&map, e))
+ * printf("found more: %l %s\n", e->key, e->value);
+ * }
+ * }
+ *
+ * if (!strcmp("has_exact_match", action)) {
+ * flags |= COMPARE_VALUE;
+ *
+ * struct long2string *e;
+ * e = malloc(sizeof(struct long2string) + strlen(value));
+ * hashmap_entry_init(e, memhash(&key, sizeof(long)));
+ * e->key = key;
+ * memcpy(e->value, value, strlen(value));
+ *
+ * printf("%s found\n", hashmap_get(&map, e, NULL) ? "" : "not");
+ * }
+ *
+ * if (!strcmp("has_exact_match_no_heap_alloc", action)) {
+ * flags |= COMPARE_VALUE;
+ *
+ * struct long2string e;
+ * hashmap_entry_init(e, memhash(&key, sizeof(long)));
+ * e.key = key;
+ *
+ * printf("%s found\n", hashmap_get(&map, e, value) ? "" : "not");
+ * }
+ *
+ * if (!strcmp("end", action)) {
+ * hashmap_free(&map, 1);
+ * break;
+ * }
+ * }
+ * }
*/
-/* FNV-1 functions */
-
+/*
+ * Ready-to-use hash functions for strings, using the FNV-1 algorithm (see
+ * http://www.isthe.com/chongo/tech/comp/fnv).
+ * `strhash` and `strihash` take 0-terminated strings, while `memhash` and
+ * `memihash` operate on arbitrary-length memory.
+ * `strihash` and `memihash` are case insensitive versions.
+ * `memihash_cont` is a variant of `memihash` that allows a computation to be
+ * continued with another chunk of data.
+ */
extern unsigned int strhash(const char *buf);
extern unsigned int strihash(const char *buf);
extern unsigned int memhash(const void *buf, size_t len);
extern unsigned int memihash(const void *buf, size_t len);
extern unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len);
+/*
+ * Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code
+ * for use in hash tables. Cryptographic hashes are supposed to have
+ * uniform distribution, so in contrast to `memhash()`, this just copies
+ * the first `sizeof(int)` bytes without shuffling any bits. Note that
+ * the results will be different on big-endian and little-endian
+ * platforms, so they should not be stored or transferred over the net.
+ */
static inline unsigned int sha1hash(const unsigned char *sha1)
{
/*
return hash;
}
-/* data structures */
-
+/*
+ * struct hashmap_entry is an opaque structure representing an entry in the
+ * hash table, which must be used as first member of user data structures.
+ * Ideally it should be followed by an int-sized member to prevent unused
+ * memory on 64-bit systems due to alignment.
+ */
struct hashmap_entry {
+ /*
+ * next points to the next entry in case of collisions (i.e. if
+ * multiple entries map to the same bucket)
+ */
struct hashmap_entry *next;
+
+ /* entry's hash code */
unsigned int hash;
};
-typedef int (*hashmap_cmp_fn)(const void *entry, const void *entry_or_key,
- const void *keydata);
+/*
+ * User-supplied function to test two hashmap entries for equality. Shall
+ * return 0 if the entries are equal.
+ *
+ * This function is always called with non-NULL `entry` and `entry_or_key`
+ * parameters that have the same hash code.
+ *
+ * When looking up an entry, the `key` and `keydata` parameters to hashmap_get
+ * and hashmap_remove are always passed as second `entry_or_key` and third
+ * argument `keydata`, respectively. Otherwise, `keydata` is NULL.
+ *
+ * When it is too expensive to allocate a user entry (either because it is
+ * large or varialbe sized, such that it is not on the stack), then the
+ * relevant data to check for equality should be passed via `keydata`.
+ * In this case `key` can be a stripped down version of the user key data
+ * or even just a hashmap_entry having the correct hash.
+ *
+ * The `hashmap_cmp_fn_data` entry is the pointer given in the init function.
+ */
+typedef int (*hashmap_cmp_fn)(const void *hashmap_cmp_fn_data,
+ const void *entry, const void *entry_or_key,
+ const void *keydata);
+/*
+ * struct hashmap is the hash table structure. Members can be used as follows,
+ * but should not be modified directly.
+ */
struct hashmap {
struct hashmap_entry **table;
+
+ /* Stores the comparison function specified in `hashmap_init()`. */
hashmap_cmp_fn cmpfn;
- unsigned int size, tablesize, grow_at, shrink_at;
- unsigned disallow_rehash : 1;
-};
+ const void *cmpfn_data;
-struct hashmap_iter {
- struct hashmap *map;
- struct hashmap_entry *next;
- unsigned int tablepos;
+ /* total number of entries (0 means the hashmap is empty) */
+ unsigned int size;
+
+ /*
+ * tablesize is the allocated size of the hash table. A non-0 value
+ * indicates that the hashmap is initialized. It may also be useful
+ * for statistical purposes (i.e. `size / tablesize` is the current
+ * load factor).
+ */
+ unsigned int tablesize;
+
+ unsigned int grow_at;
+ unsigned int shrink_at;
+
+ /* See `hashmap_disallow_rehash`. */
+ unsigned disallow_rehash : 1;
};
/* hashmap functions */
-extern void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
- size_t initial_size);
+/*
+ * Initializes a hashmap structure.
+ *
+ * `map` is the hashmap to initialize.
+ *
+ * The `equals_function` can be specified to compare two entries for equality.
+ * If NULL, entries are considered equal if their hash codes are equal.
+ *
+ * The `equals_function_data` parameter can be used to provide additional data
+ * (a callback cookie) that will be passed to `equals_function` each time it
+ * is called. This allows a single `equals_function` to implement multiple
+ * comparison functions.
+ *
+ * If the total number of entries is known in advance, the `initial_size`
+ * parameter may be used to preallocate a sufficiently large table and thus
+ * prevent expensive resizing. If 0, the table is dynamically resized.
+ */
+extern void hashmap_init(struct hashmap *map,
+ hashmap_cmp_fn equals_function,
+ const void *equals_function_data,
+ size_t initial_size);
+
+/*
+ * Frees a hashmap structure and allocated memory.
+ *
+ * If `free_entries` is true, each hashmap_entry in the map is freed as well
+ * using stdlibs free().
+ */
extern void hashmap_free(struct hashmap *map, int free_entries);
/* hashmap_entry functions */
+/*
+ * Initializes a hashmap_entry structure.
+ *
+ * `entry` points to the entry to initialize.
+ * `hash` is the hash code of the entry.
+ *
+ * The hashmap_entry structure does not hold references to external resources,
+ * and it is safe to just discard it once you are done with it (i.e. if
+ * your structure was allocated with xmalloc(), you can just free(3) it,
+ * and if it is on stack, you can just let it go out of scope).
+ */
static inline void hashmap_entry_init(void *entry, unsigned int hash)
{
struct hashmap_entry *e = entry;
e->hash = hash;
e->next = NULL;
}
+
+/*
+ * Returns the hashmap entry for the specified key, or NULL if not found.
+ *
+ * `map` is the hashmap structure.
+ *
+ * `key` is a user data structure that starts with hashmap_entry that has at
+ * least been initialized with the proper hash code (via `hashmap_entry_init`).
+ *
+ * `keydata` is a data structure that holds just enough information to check
+ * for equality to a given entry.
+ *
+ * If the key data is variable-sized (e.g. a FLEX_ARRAY string) or quite large,
+ * it is undesirable to create a full-fledged entry structure on the heap and
+ * copy all the key data into the structure.
+ *
+ * In this case, the `keydata` parameter can be used to pass
+ * variable-sized key data directly to the comparison function, and the `key`
+ * parameter can be a stripped-down, fixed size entry structure allocated on the
+ * stack.
+ *
+ * If an entry with matching hash code is found, `key` and `keydata` are passed
+ * to `hashmap_cmp_fn` to decide whether the entry matches the key.
+ */
extern void *hashmap_get(const struct hashmap *map, const void *key,
- const void *keydata);
-extern void *hashmap_get_next(const struct hashmap *map, const void *entry);
-extern void hashmap_add(struct hashmap *map, void *entry);
-extern void *hashmap_put(struct hashmap *map, void *entry);
-extern void *hashmap_remove(struct hashmap *map, const void *key,
- const void *keydata);
+ const void *keydata);
+/*
+ * Returns the hashmap entry for the specified hash code and key data,
+ * or NULL if not found.
+ *
+ * `map` is the hashmap structure.
+ * `hash` is the hash code of the entry to look up.
+ *
+ * If an entry with matching hash code is found, `keydata` is passed to
+ * `hashmap_cmp_fn` to decide whether the entry matches the key. The
+ * `entry_or_key` parameter of `hashmap_cmp_fn` points to a hashmap_entry
+ * structure that should not be used in the comparison.
+ */
static inline void *hashmap_get_from_hash(const struct hashmap *map,
- unsigned int hash, const void *keydata)
+ unsigned int hash,
+ const void *keydata)
{
struct hashmap_entry key;
hashmap_entry_init(&key, hash);
return hashmap_get(map, &key, keydata);
}
+/*
+ * Returns the next equal hashmap entry, or NULL if not found. This can be
+ * used to iterate over duplicate entries (see `hashmap_add`).
+ *
+ * `map` is the hashmap structure.
+ * `entry` is the hashmap_entry to start the search from, obtained via a previous
+ * call to `hashmap_get` or `hashmap_get_next`.
+ */
+extern void *hashmap_get_next(const struct hashmap *map, const void *entry);
+
+/*
+ * Adds a hashmap entry. This allows to add duplicate entries (i.e.
+ * separate values with the same key according to hashmap_cmp_fn).
+ *
+ * `map` is the hashmap structure.
+ * `entry` is the entry to add.
+ */
+extern void hashmap_add(struct hashmap *map, void *entry);
+
+/*
+ * Adds or replaces a hashmap entry. If the hashmap contains duplicate
+ * entries equal to the specified entry, only one of them will be replaced.
+ *
+ * `map` is the hashmap structure.
+ * `entry` is the entry to add or replace.
+ * Returns the replaced entry, or NULL if not found (i.e. the entry was added).
+ */
+extern void *hashmap_put(struct hashmap *map, void *entry);
+
+/*
+ * Removes a hashmap entry matching the specified key. If the hashmap contains
+ * duplicate entries equal to the specified key, only one of them will be
+ * removed. Returns the removed entry, or NULL if not found.
+ *
+ * Argument explanation is the same as in `hashmap_get`.
+ */
+extern void *hashmap_remove(struct hashmap *map, const void *key,
+ const void *keydata);
+
+/*
+ * Returns the `bucket` an entry is stored in.
+ * Useful for multithreaded read access.
+ */
int hashmap_bucket(const struct hashmap *map, unsigned int hash);
/*
* Disallow/allow rehashing of the hashmap.
- * This is useful if the caller knows that the hashmap
- * needs multi-threaded access. The caller is still
- * required to guard/lock searches and inserts in a
- * manner appropriate to their usage. This simply
- * prevents the table from being unexpectedly re-mapped.
+ * This is useful if the caller knows that the hashmap needs multi-threaded
+ * access. The caller is still required to guard/lock searches and inserts
+ * in a manner appropriate to their usage. This simply prevents the table
+ * from being unexpectedly re-mapped.
*
- * If is up to the caller to ensure that the hashmap is
- * initialized to a reasonable size to prevent poor
- * performance.
+ * It is up to the caller to ensure that the hashmap is initialized to a
+ * reasonable size to prevent poor performance.
*
- * When value=1, prevent future rehashes on adds and deleted.
- * When value=0, allow future rehahses. This DOES NOT force
- * a rehash now.
+ * A call to allow rehashing does not force a rehash; that might happen
+ * with the next insert or delete.
*/
static inline void hashmap_disallow_rehash(struct hashmap *map, unsigned value)
{
map->disallow_rehash = value;
}
-/* hashmap_iter functions */
+/*
+ * Used to iterate over all entries of a hashmap. Note that it is
+ * not safe to add or remove entries to the hashmap while
+ * iterating.
+ */
+struct hashmap_iter {
+ struct hashmap *map;
+ struct hashmap_entry *next;
+ unsigned int tablepos;
+};
+/* Initializes a `hashmap_iter` structure. */
extern void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter);
+
+/* Returns the next hashmap_entry, or NULL if there are no more entries. */
extern void *hashmap_iter_next(struct hashmap_iter *iter);
+
+/* Initializes the iterator and returns the first entry, if any. */
static inline void *hashmap_iter_first(struct hashmap *map,
struct hashmap_iter *iter)
{
return hashmap_iter_next(iter);
}
-/* string interning */
+/* String interning */
+/*
+ * Returns the unique, interned version of the specified string or data,
+ * similar to the `String.intern` API in Java and .NET, respectively.
+ * Interned strings remain valid for the entire lifetime of the process.
+ *
+ * Can be used as `[x]strdup()` or `xmemdupz` replacement, except that interned
+ * strings / data must not be modified or freed.
+ *
+ * Interned strings are best used for short strings with high probability of
+ * duplicates.
+ *
+ * Uses a hashmap to store the pool of interned strings.
+ */
extern const void *memintern(const void *data, size_t len);
static inline const char *strintern(const char *string)
{
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