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// This is an implementation of the open-addressing hash table.
#include "chibicc.h"
#define HASHMAP_C "hashmap.c"
// Initial hash bucket size
#define INIT_SIZE 16
// Rehash if the usage exceeds 70%.
#define HIGH_WATERMARK 70
// We'll keep the usage below 50% after rehashing.
#define LOW_WATERMARK 50
// Represents a deleted hash entry
#define TOMBSTONE ((void *)-1)
static uint64_t fnv_hash(char *s, int len)
{
uint64_t hash = 0xcbf29ce484222325;
for (int i = 0; i < len; i++)
{
hash *= 0x100000001b3;
hash ^= (unsigned char)s[i];
}
return hash;
}
// Make room for new entries in a given hashmap by removing
// tombstones and possibly extending the bucket size.
static void rehash(HashMap *map)
{
// Compute the size of the new hashmap.
int nkeys = 0;
for (int i = 0; i < map->capacity; i++)
if (map->buckets[i].key && map->buckets[i].key != TOMBSTONE)
nkeys++;
int cap = map->capacity;
while ((nkeys * 100) / cap >= LOW_WATERMARK)
cap = cap * 2;
assert(cap > 0);
// Create a new hashmap and copy all key-values.
HashMap map2 = {};
map2.buckets = calloc(cap, sizeof(HashEntry));
if (map2.buckets == NULL)
error("%s: in rehash map2.buckets is null!", HASHMAP_C);
map2.capacity = cap;
for (int i = 0; i < map->capacity; i++)
{
HashEntry *ent = &map->buckets[i];
if (ent->key && ent->key != TOMBSTONE)
hashmap_put2(&map2, ent->key, ent->keylen, ent->val);
}
assert(map2.used == nkeys);
*map = map2;
}
static bool match(HashEntry *ent, char *key, int keylen)
{
return ent->key && ent->key != TOMBSTONE &&
ent->keylen == keylen && memcmp(ent->key, key, keylen) == 0;
}
static HashEntry *get_entry(HashMap *map, char *key, int keylen)
{
if (!map->buckets)
return NULL;
uint64_t hash = fnv_hash(key, keylen);
for (int i = 0; i < map->capacity; i++)
{
HashEntry *ent = &map->buckets[(hash + i) % map->capacity];
if (match(ent, key, keylen))
return ent;
if (ent->key == NULL)
return NULL;
}
unreachable();
}
static HashEntry *get_or_insert_entry(HashMap *map, char *key, int keylen)
{
if (!map->buckets)
{
map->buckets = calloc(INIT_SIZE, sizeof(HashEntry));
if (map->buckets == NULL)
error("%s: in get_or_insert_entry map->buckets is null!", HASHMAP_C);
map->capacity = INIT_SIZE;
}
else if ((map->used * 100) / map->capacity >= HIGH_WATERMARK)
{
rehash(map);
}
uint64_t hash = fnv_hash(key, keylen);
for (int i = 0; i < map->capacity; i++)
{
HashEntry *ent = &map->buckets[(hash + i) % map->capacity];
if (match(ent, key, keylen))
return ent;
// if (ent->key == TOMBSTONE)
// {
// ent->key = key;
// ent->keylen = keylen;
// return ent;
// }
if (ent->key == NULL)
{
ent->key = key;
ent->keylen = keylen;
map->used++;
return ent;
}
}
unreachable();
}
void *hashmap_get(HashMap *map, char *key)
{
return hashmap_get2(map, key, strlen(key));
}
void *hashmap_get2(HashMap *map, char *key, int keylen)
{
HashEntry *ent = get_entry(map, key, keylen);
return ent ? ent->val : NULL;
}
void hashmap_put(HashMap *map, char *key, void *val)
{
hashmap_put2(map, key, strlen(key), val);
}
void hashmap_put2(HashMap *map, char *key, int keylen, void *val)
{
HashEntry *ent = get_or_insert_entry(map, key, keylen);
ent->val = val;
}
void hashmap_delete(HashMap *map, char *key)
{
hashmap_delete2(map, key, strlen(key));
}
void hashmap_delete2(HashMap *map, char *key, int keylen)
{
HashEntry *ent = get_entry(map, key, keylen);
if (ent)
ent->key = TOMBSTONE;
}
void hashmap_test(void)
{
HashMap *map = calloc(1, sizeof(HashMap));
for (int i = 0; i < 5000; i++)
hashmap_put(map, format("key %d", i), (void *)(size_t)i);
for (int i = 1000; i < 2000; i++)
hashmap_delete(map, format("key %d", i));
for (int i = 1500; i < 1600; i++)
hashmap_put(map, format("key %d", i), (void *)(size_t)i);
for (int i = 6000; i < 7000; i++)
hashmap_put(map, format("key %d", i), (void *)(size_t)i);
for (int i = 0; i < 1000; i++)
assert((size_t)hashmap_get(map, format("key %d", i)) == i);
for (int i = 1000; i < 1500; i++)
assert(hashmap_get(map, "no such key") == NULL);
for (int i = 1500; i < 1600; i++)
assert((size_t)hashmap_get(map, format("key %d", i)) == i);
for (int i = 1600; i < 2000; i++)
assert(hashmap_get(map, "no such key") == NULL);
for (int i = 2000; i < 5000; i++)
assert((size_t)hashmap_get(map, format("key %d", i)) == i);
for (int i = 5000; i < 6000; i++)
assert(hashmap_get(map, "no such key") == NULL);
for (int i = 6000; i < 7000; i++)
hashmap_put(map, format("key %d", i), (void *)(size_t)i);
assert(hashmap_get(map, "no such key") == NULL);
free(map);
}
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