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d40abc8e95
There are no callers left of sha1hash() that do not simply pass the "hash" member of a "struct object_id". Let's get rid of the outdated sha1-specific function and provide one that operates on the whole struct (even though the technique, taking the first few bytes of the hash, will remain the same). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
441 lines
14 KiB
C
441 lines
14 KiB
C
#ifndef HASHMAP_H
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#define HASHMAP_H
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#include "hash.h"
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/*
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* Generic implementation of hash-based key-value mappings.
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*
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* An example that maps long to a string:
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* For the sake of the example this allows to lookup exact values, too
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* (i.e. it is operated as a set, the value is part of the key)
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* -------------------------------------
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*
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* struct hashmap map;
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* struct long2string {
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* struct hashmap_entry ent; // must be the first member!
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* long key;
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* char value[FLEX_ARRAY]; // be careful with allocating on stack!
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* };
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*
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* #define COMPARE_VALUE 1
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*
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* static int long2string_cmp(const void *hashmap_cmp_fn_data,
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* const struct long2string *e1,
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* const struct long2string *e2,
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* const void *keydata)
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* {
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* const char *string = keydata;
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* unsigned flags = *(unsigned *)hashmap_cmp_fn_data;
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*
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* if (flags & COMPARE_VALUE)
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* return e1->key != e2->key ||
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* strcmp(e1->value, string ? string : e2->value);
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* else
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* return e1->key != e2->key;
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* }
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*
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* int main(int argc, char **argv)
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* {
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* long key;
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* char value[255], action[32];
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* unsigned flags = 0;
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*
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* hashmap_init(&map, (hashmap_cmp_fn) long2string_cmp, &flags, 0);
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*
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* while (scanf("%s %ld %s", action, &key, value)) {
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*
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* if (!strcmp("add", action)) {
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* struct long2string *e;
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* FLEX_ALLOC_STR(e, value, value);
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* hashmap_entry_init(e, memhash(&key, sizeof(long)));
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* e->key = key;
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* hashmap_add(&map, e);
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* }
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*
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* if (!strcmp("print_all_by_key", action)) {
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* struct long2string k, *e;
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* hashmap_entry_init(&k, memhash(&key, sizeof(long)));
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* k.key = key;
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*
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* flags &= ~COMPARE_VALUE;
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* e = hashmap_get(&map, &k, NULL);
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* if (e) {
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* printf("first: %ld %s\n", e->key, e->value);
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* while ((e = hashmap_get_next(&map, e)))
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* printf("found more: %ld %s\n", e->key, e->value);
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* }
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* }
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*
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* if (!strcmp("has_exact_match", action)) {
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* struct long2string *e;
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* FLEX_ALLOC_STR(e, value, value);
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* hashmap_entry_init(e, memhash(&key, sizeof(long)));
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* e->key = key;
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*
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* flags |= COMPARE_VALUE;
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* printf("%sfound\n", hashmap_get(&map, e, NULL) ? "" : "not ");
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* free(e);
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* }
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*
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* if (!strcmp("has_exact_match_no_heap_alloc", action)) {
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* struct long2string k;
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* hashmap_entry_init(&k, memhash(&key, sizeof(long)));
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* k.key = key;
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*
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* flags |= COMPARE_VALUE;
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* printf("%sfound\n", hashmap_get(&map, &k, value) ? "" : "not ");
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* }
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*
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* if (!strcmp("end", action)) {
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* hashmap_free(&map, 1);
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* break;
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* }
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* }
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*
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* return 0;
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* }
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*/
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/*
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* Ready-to-use hash functions for strings, using the FNV-1 algorithm (see
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* http://www.isthe.com/chongo/tech/comp/fnv).
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* `strhash` and `strihash` take 0-terminated strings, while `memhash` and
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* `memihash` operate on arbitrary-length memory.
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* `strihash` and `memihash` are case insensitive versions.
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* `memihash_cont` is a variant of `memihash` that allows a computation to be
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* continued with another chunk of data.
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*/
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unsigned int strhash(const char *buf);
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unsigned int strihash(const char *buf);
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unsigned int memhash(const void *buf, size_t len);
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unsigned int memihash(const void *buf, size_t len);
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unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len);
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/*
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* Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code
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* for use in hash tables. Cryptographic hashes are supposed to have
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* uniform distribution, so in contrast to `memhash()`, this just copies
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* the first `sizeof(int)` bytes without shuffling any bits. Note that
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* the results will be different on big-endian and little-endian
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* platforms, so they should not be stored or transferred over the net.
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*/
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static inline unsigned int oidhash(const struct object_id *oid)
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{
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/*
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* Equivalent to 'return *(unsigned int *)oid->hash;', but safe on
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* platforms that don't support unaligned reads.
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*/
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unsigned int hash;
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memcpy(&hash, oid->hash, sizeof(hash));
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return hash;
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}
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/*
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* struct hashmap_entry is an opaque structure representing an entry in the
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* hash table, which must be used as first member of user data structures.
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* Ideally it should be followed by an int-sized member to prevent unused
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* memory on 64-bit systems due to alignment.
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*/
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struct hashmap_entry {
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/*
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* next points to the next entry in case of collisions (i.e. if
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* multiple entries map to the same bucket)
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*/
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struct hashmap_entry *next;
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/* entry's hash code */
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unsigned int hash;
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};
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/*
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* User-supplied function to test two hashmap entries for equality. Shall
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* return 0 if the entries are equal.
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*
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* This function is always called with non-NULL `entry` and `entry_or_key`
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* parameters that have the same hash code.
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*
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* When looking up an entry, the `key` and `keydata` parameters to hashmap_get
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* and hashmap_remove are always passed as second `entry_or_key` and third
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* argument `keydata`, respectively. Otherwise, `keydata` is NULL.
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*
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* When it is too expensive to allocate a user entry (either because it is
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* large or varialbe sized, such that it is not on the stack), then the
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* relevant data to check for equality should be passed via `keydata`.
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* In this case `key` can be a stripped down version of the user key data
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* or even just a hashmap_entry having the correct hash.
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*
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* The `hashmap_cmp_fn_data` entry is the pointer given in the init function.
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*/
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typedef int (*hashmap_cmp_fn)(const void *hashmap_cmp_fn_data,
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const void *entry, const void *entry_or_key,
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const void *keydata);
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/*
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* struct hashmap is the hash table structure. Members can be used as follows,
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* but should not be modified directly.
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*/
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struct hashmap {
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struct hashmap_entry **table;
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/* Stores the comparison function specified in `hashmap_init()`. */
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hashmap_cmp_fn cmpfn;
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const void *cmpfn_data;
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/* total number of entries (0 means the hashmap is empty) */
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unsigned int private_size; /* use hashmap_get_size() */
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/*
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* tablesize is the allocated size of the hash table. A non-0 value
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* indicates that the hashmap is initialized. It may also be useful
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* for statistical purposes (i.e. `size / tablesize` is the current
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* load factor).
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*/
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unsigned int tablesize;
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unsigned int grow_at;
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unsigned int shrink_at;
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unsigned int do_count_items : 1;
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};
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/* hashmap functions */
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/*
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* Initializes a hashmap structure.
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*
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* `map` is the hashmap to initialize.
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*
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* The `equals_function` can be specified to compare two entries for equality.
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* If NULL, entries are considered equal if their hash codes are equal.
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*
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* The `equals_function_data` parameter can be used to provide additional data
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* (a callback cookie) that will be passed to `equals_function` each time it
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* is called. This allows a single `equals_function` to implement multiple
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* comparison functions.
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*
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* If the total number of entries is known in advance, the `initial_size`
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* parameter may be used to preallocate a sufficiently large table and thus
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* prevent expensive resizing. If 0, the table is dynamically resized.
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*/
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void hashmap_init(struct hashmap *map,
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hashmap_cmp_fn equals_function,
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const void *equals_function_data,
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size_t initial_size);
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/*
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* Frees a hashmap structure and allocated memory.
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*
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* If `free_entries` is true, each hashmap_entry in the map is freed as well
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* using stdlibs free().
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*/
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void hashmap_free(struct hashmap *map, int free_entries);
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/* hashmap_entry functions */
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/*
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* Initializes a hashmap_entry structure.
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*
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* `entry` points to the entry to initialize.
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* `hash` is the hash code of the entry.
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*
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* The hashmap_entry structure does not hold references to external resources,
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* and it is safe to just discard it once you are done with it (i.e. if
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* your structure was allocated with xmalloc(), you can just free(3) it,
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* and if it is on stack, you can just let it go out of scope).
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*/
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static inline void hashmap_entry_init(void *entry, unsigned int hash)
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{
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struct hashmap_entry *e = entry;
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e->hash = hash;
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e->next = NULL;
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}
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/*
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* Return the number of items in the map.
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*/
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static inline unsigned int hashmap_get_size(struct hashmap *map)
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{
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if (map->do_count_items)
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return map->private_size;
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BUG("hashmap_get_size: size not set");
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return 0;
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}
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/*
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* Returns the hashmap entry for the specified key, or NULL if not found.
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*
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* `map` is the hashmap structure.
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*
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* `key` is a user data structure that starts with hashmap_entry that has at
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* least been initialized with the proper hash code (via `hashmap_entry_init`).
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*
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* `keydata` is a data structure that holds just enough information to check
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* for equality to a given entry.
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*
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* If the key data is variable-sized (e.g. a FLEX_ARRAY string) or quite large,
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* it is undesirable to create a full-fledged entry structure on the heap and
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* copy all the key data into the structure.
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*
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* In this case, the `keydata` parameter can be used to pass
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* variable-sized key data directly to the comparison function, and the `key`
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* parameter can be a stripped-down, fixed size entry structure allocated on the
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* stack.
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*
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* If an entry with matching hash code is found, `key` and `keydata` are passed
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* to `hashmap_cmp_fn` to decide whether the entry matches the key.
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*/
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void *hashmap_get(const struct hashmap *map, const void *key,
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const void *keydata);
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/*
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* Returns the hashmap entry for the specified hash code and key data,
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* or NULL if not found.
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*
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* `map` is the hashmap structure.
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* `hash` is the hash code of the entry to look up.
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*
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* If an entry with matching hash code is found, `keydata` is passed to
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* `hashmap_cmp_fn` to decide whether the entry matches the key. The
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* `entry_or_key` parameter of `hashmap_cmp_fn` points to a hashmap_entry
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* structure that should not be used in the comparison.
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*/
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static inline void *hashmap_get_from_hash(const struct hashmap *map,
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unsigned int hash,
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const void *keydata)
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{
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struct hashmap_entry key;
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hashmap_entry_init(&key, hash);
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return hashmap_get(map, &key, keydata);
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}
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/*
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* Returns the next equal hashmap entry, or NULL if not found. This can be
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* used to iterate over duplicate entries (see `hashmap_add`).
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*
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* `map` is the hashmap structure.
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* `entry` is the hashmap_entry to start the search from, obtained via a previous
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* call to `hashmap_get` or `hashmap_get_next`.
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*/
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void *hashmap_get_next(const struct hashmap *map, const void *entry);
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/*
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* Adds a hashmap entry. This allows to add duplicate entries (i.e.
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* separate values with the same key according to hashmap_cmp_fn).
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*
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* `map` is the hashmap structure.
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* `entry` is the entry to add.
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*/
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void hashmap_add(struct hashmap *map, void *entry);
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/*
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* Adds or replaces a hashmap entry. If the hashmap contains duplicate
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* entries equal to the specified entry, only one of them will be replaced.
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*
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* `map` is the hashmap structure.
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* `entry` is the entry to add or replace.
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* Returns the replaced entry, or NULL if not found (i.e. the entry was added).
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*/
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void *hashmap_put(struct hashmap *map, void *entry);
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/*
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* Removes a hashmap entry matching the specified key. If the hashmap contains
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* duplicate entries equal to the specified key, only one of them will be
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* removed. Returns the removed entry, or NULL if not found.
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*
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* Argument explanation is the same as in `hashmap_get`.
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*/
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void *hashmap_remove(struct hashmap *map, const void *key,
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const void *keydata);
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/*
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* Returns the `bucket` an entry is stored in.
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* Useful for multithreaded read access.
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*/
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int hashmap_bucket(const struct hashmap *map, unsigned int hash);
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/*
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* Used to iterate over all entries of a hashmap. Note that it is
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* not safe to add or remove entries to the hashmap while
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* iterating.
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*/
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struct hashmap_iter {
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struct hashmap *map;
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struct hashmap_entry *next;
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unsigned int tablepos;
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};
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/* Initializes a `hashmap_iter` structure. */
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void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter);
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/* Returns the next hashmap_entry, or NULL if there are no more entries. */
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void *hashmap_iter_next(struct hashmap_iter *iter);
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/* Initializes the iterator and returns the first entry, if any. */
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static inline void *hashmap_iter_first(struct hashmap *map,
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struct hashmap_iter *iter)
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{
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hashmap_iter_init(map, iter);
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return hashmap_iter_next(iter);
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}
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/*
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* Disable item counting and automatic rehashing when adding/removing items.
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*
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* Normally, the hashmap keeps track of the number of items in the map
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* and uses it to dynamically resize it. This (both the counting and
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* the resizing) can cause problems when the map is being used by
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* threaded callers (because the hashmap code does not know about the
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* locking strategy used by the threaded callers and therefore, does
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* not know how to protect the "private_size" counter).
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*/
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static inline void hashmap_disable_item_counting(struct hashmap *map)
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{
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map->do_count_items = 0;
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}
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/*
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* Re-enable item couting when adding/removing items.
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* If counting is currently disabled, it will force count them.
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* It WILL NOT automatically rehash them.
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*/
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static inline void hashmap_enable_item_counting(struct hashmap *map)
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{
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unsigned int n = 0;
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struct hashmap_iter iter;
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if (map->do_count_items)
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return;
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hashmap_iter_init(map, &iter);
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while (hashmap_iter_next(&iter))
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n++;
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map->do_count_items = 1;
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map->private_size = n;
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}
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/* String interning */
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/*
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* Returns the unique, interned version of the specified string or data,
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* similar to the `String.intern` API in Java and .NET, respectively.
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* Interned strings remain valid for the entire lifetime of the process.
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*
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* Can be used as `[x]strdup()` or `xmemdupz` replacement, except that interned
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* strings / data must not be modified or freed.
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*
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* Interned strings are best used for short strings with high probability of
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* duplicates.
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*
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* Uses a hashmap to store the pool of interned strings.
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*/
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const void *memintern(const void *data, size_t len);
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static inline const char *strintern(const char *string)
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{
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return memintern(string, strlen(string));
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}
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#endif
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