/src/libbpf/src/hashmap.h

Source
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */

/*
 * Generic non-thread safe hash map implementation.
 *
 * Copyright (c) 2019 Facebook
 */
#ifndef __LIBBPF_HASHMAP_H
#define __LIBBPF_HASHMAP_H

#include <stdbool.h>
#include <stddef.h>
#include <limits.h>

static inline size_t hash_bits(size_t h, int bits)
{
  /* shuffle bits and return requested number of upper bits */
  if (bits == 0)
    return 0;

#if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__)
  /* LP64 case */
  return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits);
#elif (__SIZEOF_SIZE_T__ <= __SIZEOF_LONG__)
  return (h * 2654435769lu) >> (__SIZEOF_LONG__ * 8 - bits);
#else
# error "Unsupported size_t size"
#endif
}

/* generic C-string hashing function */
static inline size_t str_hash(const char *s)
{
  size_t h = 0;

  while (*s) {
    h = h * 31 + *s;
    s++;
  }
  return h;
}

typedef size_t (*hashmap_hash_fn)(long key, void *ctx);
typedef bool (*hashmap_equal_fn)(long key1, long key2, void *ctx);

/*
 * Hashmap interface is polymorphic, keys and values could be either
 * long-sized integers or pointers, this is achieved as follows:
 * - interface functions that operate on keys and values are hidden
 *   behind auxiliary macros, e.g. hashmap_insert <-> hashmap__insert;
 * - these auxiliary macros cast the key and value parameters as
 *   long or long *, so the user does not have to specify the casts explicitly;
 * - for pointer parameters (e.g. old_key) the size of the pointed
 *   type is verified by hashmap_cast_ptr using _Static_assert;
 * - when iterating using hashmap__for_each_* forms
 *   hasmap_entry->key should be used for integer keys and
 *   hasmap_entry->pkey should be used for pointer keys,
 *   same goes for values.
 */
struct hashmap_entry {
  union {
    long key;
    const void *pkey;
  };
  union {
    long value;
    void *pvalue;
  };
  struct hashmap_entry *next;
};

struct hashmap {
  hashmap_hash_fn hash_fn;
  hashmap_equal_fn equal_fn;
  void *ctx;

  struct hashmap_entry **buckets;
  size_t cap;
  size_t cap_bits;
  size_t sz;
};

void hashmap__init(struct hashmap *map, hashmap_hash_fn hash_fn,
       hashmap_equal_fn equal_fn, void *ctx);
struct hashmap *hashmap__new(hashmap_hash_fn hash_fn,
           hashmap_equal_fn equal_fn,
           void *ctx);
void hashmap__clear(struct hashmap *map);
void hashmap__free(struct hashmap *map);

size_t hashmap__size(const struct hashmap *map);
size_t hashmap__capacity(const struct hashmap *map);

/*
 * Hashmap insertion strategy:
 * - HASHMAP_ADD - only add key/value if key doesn't exist yet;
 * - HASHMAP_SET - add key/value pair if key doesn't exist yet; otherwise,
 *   update value;
 * - HASHMAP_UPDATE - update value, if key already exists; otherwise, do
 *   nothing and return -ENOENT;
 * - HASHMAP_APPEND - always add key/value pair, even if key already exists.
 *   This turns hashmap into a multimap by allowing multiple values to be
 *   associated with the same key. Most useful read API for such hashmap is
 *   hashmap__for_each_key_entry() iteration. If hashmap__find() is still
 *   used, it will return last inserted key/value entry (first in a bucket
 *   chain).
 */
enum hashmap_insert_strategy {
  HASHMAP_ADD,
  HASHMAP_SET,
  HASHMAP_UPDATE,
  HASHMAP_APPEND,
};

#define hashmap_cast_ptr(p) ({                \
  _Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) ||     \
        sizeof(*(p)) == sizeof(long),       \
           #p " pointee should be a long-sized integer or a pointer");  \
  (long *)(p);                  \
})

/*
 * hashmap__insert() adds key/value entry w/ various semantics, depending on
 * provided strategy value. If a given key/value pair replaced already
 * existing key/value pair, both old key and old value will be returned
 * through old_key and old_value to allow calling code do proper memory
 * management.
 */
int hashmap_insert(struct hashmap *map, long key, long value,
       enum hashmap_insert_strategy strategy,
       long *old_key, long *old_value);

#define hashmap__insert(map, key, value, strategy, old_key, old_value) \
  hashmap_insert((map), (long)(key), (long)(value), (strategy),  \
           hashmap_cast_ptr(old_key),           \
           hashmap_cast_ptr(old_value))

#define hashmap__add(map, key, value) \
  hashmap__insert((map), (key), (value), HASHMAP_ADD, NULL, NULL)

#define hashmap__set(map, key, value, old_key, old_value) \
  hashmap__insert((map), (key), (value), HASHMAP_SET, (old_key), (old_value))

#define hashmap__update(map, key, value, old_key, old_value) \
  hashmap__insert((map), (key), (value), HASHMAP_UPDATE, (old_key), (old_value))

#define hashmap__append(map, key, value) \
  hashmap__insert((map), (key), (value), HASHMAP_APPEND, NULL, NULL)

bool hashmap_delete(struct hashmap *map, long key, long *old_key, long *old_value);

#define hashmap__delete(map, key, old_key, old_value)          \
  hashmap_delete((map), (long)(key),             \
           hashmap_cast_ptr(old_key),          \
           hashmap_cast_ptr(old_value))

bool hashmap_find(const struct hashmap *map, long key, long *value);

#define hashmap__find(map, key, value) \
  hashmap_find((map), (long)(key), hashmap_cast_ptr(value))

/*
 * hashmap__for_each_entry - iterate over all entries in hashmap
 * @map: hashmap to iterate
 * @cur: struct hashmap_entry * used as a loop cursor
 * @bkt: integer used as a bucket loop cursor
 */
#define hashmap__for_each_entry(map, cur, bkt)            \
  for (bkt = 0; bkt < (map)->cap; bkt++)           \
    for (cur = (map)->buckets[bkt]; cur; cur = cur->next)

/*
 * hashmap__for_each_entry_safe - iterate over all entries in hashmap, safe
 * against removals
 * @map: hashmap to iterate
 * @cur: struct hashmap_entry * used as a loop cursor
 * @tmp: struct hashmap_entry * used as a temporary next cursor storage
 * @bkt: integer used as a bucket loop cursor
 */
#define hashmap__for_each_entry_safe(map, cur, tmp, bkt)        \
  for (bkt = 0; bkt < (map)->cap; bkt++)           \
    for (cur = (map)->buckets[bkt];           \
         cur && ({tmp = cur->next; true; });       \
         cur = tmp)

/*
 * hashmap__for_each_key_entry - iterate over entries associated with given key
 * @map: hashmap to iterate
 * @cur: struct hashmap_entry * used as a loop cursor
 * @key: key to iterate entries for
 */
#define hashmap__for_each_key_entry(map, cur, _key)         \
  for (cur = (map)->buckets              \
         ? (map)->buckets[hash_bits((map)->hash_fn((_key), (map)->ctx), (map)->cap_bits)] \
         : NULL;                \
       cur;                 \
       cur = cur->next)               \
    if ((map)->equal_fn(cur->key, (_key), (map)->ctx))

#define hashmap__for_each_key_entry_safe(map, cur, tmp, _key)       \
  for (cur = (map)->buckets             \
         ? (map)->buckets[hash_bits((map)->hash_fn((_key), (map)->ctx), (map)->cap_bits)] \
         : NULL;                \
       cur && ({ tmp = cur->next; true; });         \
       cur = tmp)                 \
    if ((map)->equal_fn(cur->key, (_key), (map)->ctx))

#endif /* __LIBBPF_HASHMAP_H */

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Created: 2025-10-13 07:02