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#ifndef BDL_HASHTABLE_H
#define BDL_HASHTABLE_H
#include "darray.h"
#include "objects.h"
// Minimum table capacity.
#define HT_MIN_CAP 4
#define HT_MIN_SHIFT 2
// Adjust the load factor threshold at which the table will grow on insertion.
#define HT_LOAD_THRESHOLD 0.75
typedef struct HashTablePair {
Object *key;
Object *value;
} HashTablePair;
typedef struct HashTable {
// All available key-value pairs as a dynamic array.
HashTablePair *pairs;
// This table expects the number of buckets to grow in powers of two. To
// speedup the default hashing, we memoize the number of bits equivalent to
// that power of 2:
//
// cap := 1024 = 2 ^ 10, shift_amount := 10
//
uint8_t shift_amount;
} HashTable;
// Use Fibonacci hashing to map a hash to a value in range of the table.
static inline uint64_t
_fibonacci_hash(uint64_t hash, size_t shift_amount) {
return (hash * UINT64_C(11400714819323198485)) >> (64 - shift_amount);
}
uint64_t
ht_hash(const HashTable *table, const Object *key) {
uint64_t hash = 0x65d9d65f6a19574f;
// printf("HASHING: ");
// display(key);
// printf("\n");
return 0;
}
static inline size_t
ht_load_factor(const HashTable *table) {
return array_size(table->pairs) / array_cap(table->pairs);
}
HashTable *
ht_init(void) {
HashTable *table = malloc(sizeof(HashTable));
table->pairs = NULL;
array_init(table->pairs, HT_MIN_CAP);
// Clear the table ensuring all references point to NULL.
for (size_t i = 0; i < array_cap(table->pairs); i++) {
table->pairs[i] = (HashTablePair){NULL, NULL};
}
table->shift_amount = HT_MIN_SHIFT;
return table;
}
void
ht_insert(HashTable *table, const Object *key, const Object *value) {
// TODO: Grow if needed.
size_t position = ht_hash(table, key);
size_t probe_position = position;
// Verify the key in that position is free. If not, use linear probing to
// find the next free slot.
HashTablePair *pairs = table->pairs;
while (true) {
if (pairs[probe_position].key == NULL) {
break;
}
if (obj_eq(pairs[probe_position].key, key)) {
break;
}
if (probe_position == array_cap(pairs)) {
probe_position = 0;
} else {
probe_position++;
}
}
pairs[probe_position].key = (Object *)key;
pairs[probe_position].value = (Object *)value;
return;
}
Object *
ht_lookup(const HashTable *table, const Object *key) {
size_t position = ht_hash(table, key);
size_t probe_position = position;
// Verify the key in that position is the same. If not perform linear
// probing to find it.
HashTablePair *pairs = table->pairs;
while (true) {
if (pairs[probe_position].key == NULL) {
return NULL;
}
if (obj_eq(pairs[probe_position].key, key)) {
break;
}
if (probe_position == array_cap(pairs)) {
probe_position = 0;
} else {
probe_position++;
}
}
return pairs[probe_position].value;
}
void
ht_debug(HashTable *table) {
HashTablePair *pairs = table->pairs;
for (size_t i = 0; i < array_cap(pairs); i++) {
printf("i: %ld ", i);
if (pairs[i].key == NULL) {
printf("EMPTY\n");
} else {
printf("key: ");
display(pairs[i].key);
printf(" value: ");
display(pairs[i].value);
printf("\n");
}
}
}
// // Use Fibonacci hashing to map a hash to a value in range of the table.
// static inline
// uint64_t _fibonacci_hash(uint64_t hash, size_t shift_amount) {
// return (hash * UINT64_C(11400714819323198485)) >> (64 - shift_amount);
// }
// // Hash a null terminated string using a circular shift + XOR hash function.
// static inline
// uint64_t _string_hash(const HashStash *table, const char *key) {
// uint64_t hash = 0x65d9d65f6a19574f;
// while (*key) {
// hash ^= (uint64_t)*key++;
// hash = (hash << 8) | (hash >> (64 - 8));
// }
// return _fibonacci_hash(hash, table->shift_amount);
// }
// // Return the key as an unsigned integer.
// static inline
// uint64_t _number_hash(const HashStash *table, const char *key) {
// uint64_t hash = 0;
// memcpy(&hash, key, table->key_length);
// return _fibonacci_hash(hash, table->shift_amount);
// }
#endif // BDL_HASHTABLE_H
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