Overhaul hashmap_t functionalities

This patch fixes constracts of hashmap_t-related function, including:

- hashmap_contains: Instead of delegates to result returned by
  hashmap_get, now shares similar logic to avoid bucket node value
  being NULL and treat as false.
- hashmap_free: Now respects bucket node value's pointer, if it's
  already NULL, then hashmap won't free it.

Additionally, now hashmap_t is capable of rehashing its underlying
bucket node array when load factor reaches 75%.

Close #190.

Author: ChAoSUnItY

src/defs.h

@@ -78,6 +78,20 @@ typedef struct {
     arena_block_t *head;
 } arena_t;
 
+/* string-based hash map definitions */
+
+typedef struct hashmap_node {
+    char *key;
+    void *val;
+    struct hashmap_node *next;
+} hashmap_node_t;
+
+typedef struct {
+    int size;
+    int cap;
+    hashmap_node_t **buckets;
+} hashmap_t;
+
 /* builtin types */
 typedef enum {
     TYPE_void = 0,
@@ -331,19 +345,6 @@ typedef struct {
     int value;
 } constant_t;
 
-/* string-based hash map definitions */
-
-typedef struct hashmap_node {
-    char *key;
-    void *val;
-    struct hashmap_node *next;
-} hashmap_node_t;
-
-typedef struct {
-    int size;
-    hashmap_node_t **buckets;
-} hashmap_t;
-
 struct phi_operand {
     var_t *var;
     basic_block_t *from;

src/globals.c

@@ -231,27 +231,25 @@ int round_up_pow2(int v)
  *
  * Return: The pointer of created hashmap.
  */
-hashmap_t *hashmap_create(int size)
+hashmap_t *hashmap_create(int cap)
 {
     hashmap_t *map = malloc(sizeof(hashmap_t));
 
     if (!map) {
-        printf("Failed to allocate hashmap_t with size %d\n", size);
+        printf("Failed to allocate hashmap_t with capacity %d\n", cap);
         return NULL;
     }
 
-    map->size = round_up_pow2(size);
-    map->buckets = malloc(map->size * sizeof(hashmap_node_t *));
+    map->size = 0;
+    map->cap = round_up_pow2(cap);
+    map->buckets = calloc(map->cap, sizeof(hashmap_node_t *));
 
     if (!map->buckets) {
         printf("Failed to allocate buckets in hashmap_t\n");
         free(map);
         return NULL;
     }
 
-    for (int i = 0; i < map->size; i++)
-        map->buckets[i] = 0;
-
     return map;
 }
 
@@ -290,6 +288,47 @@ hashmap_node_t *hashmap_node_new(char *key, void *val)
     return node;
 }
 
+void hashmap_rehash(hashmap_t *map)
+{
+    if (!map)
+        return;
+
+    int old_cap = map->cap;
+    hashmap_node_t **old_buckets = map->buckets;
+
+    map->cap *= 2;
+    map->buckets = calloc(map->cap, sizeof(hashmap_node_t *));
+
+    if (!map->buckets) {
+        printf("Failed to allocate new buckets in hashmap_t\n");
+        map->buckets = old_buckets;
+        map->cap = old_cap;
+        return;
+    }
+
+    for (int i = 0; i < old_cap; i++) {
+        hashmap_node_t *cur = old_buckets[i], *next, *target_cur;
+
+        while (cur) {
+            next = cur->next;
+            cur->next = NULL;
+            int index = hashmap_hash_index(map->cap, cur->key);
+            target_cur = map->buckets[index];
+
+            if (!target_cur) {
+                map->buckets[index] = cur;
+            } else {
+                cur->next = target_cur;
+                map->buckets[index] = cur;
+            }
+
+            cur = next;
+        }
+    }
+
+    free(old_buckets);
+}
+
 /**
  * hashmap_put() - puts a key-value pair into given hashmap.
  * If key already contains a value, then replace it with new
@@ -304,42 +343,59 @@ void hashmap_put(hashmap_t *map, char *key, void *val)
     if (!map)
         return;
 
-    int index = hashmap_hash_index(map->size, key);
-    hashmap_node_t *cur = map->buckets[index];
+    int index = hashmap_hash_index(map->cap, key);
+    hashmap_node_t *cur = map->buckets[index],
+                   *new_node = hashmap_node_new(key, val);
 
     if (!cur) {
-        map->buckets[index] = hashmap_node_new(key, val);
+        map->buckets[index] = new_node;
     } else {
         while (cur->next)
             cur = cur->next;
-        cur->next = hashmap_node_new(key, val);
+        cur->next = new_node;
     }
 
-    /* TODO: Rehash if size exceeds size * load factor */
+    map->size++;
+    if ((map->cap >> 2) * 3 <= map->size)
+        hashmap_rehash(map);
 }
 
 /**
- * hashmap_get() - gets value from hashmap from given key.
+ * hashmap_get_node() - gets key-value pair node from hashmap from given key.
  * @map: The hashmap to be looked up. Must no be NULL.
  * @key: The key string. May be NULL.
  *
  * Return: The look up result, if the key-value pair entry
- * exists, then returns its value's address, NULL otherwise.
+ * exists, then returns address of itself, NULL otherwise.
  */
-void *hashmap_get(hashmap_t *map, char *key)
+hashmap_node_t *hashmap_get_node(hashmap_t *map, char *key)
 {
     if (!map)
         return NULL;
 
-    int index = hashmap_hash_index(map->size, key);
+    int index = hashmap_hash_index(map->cap, key);
 
     for (hashmap_node_t *cur = map->buckets[index]; cur; cur = cur->next)
         if (!strcmp(cur->key, key))
-            return cur->val;
+            return cur;
 
     return NULL;
 }
 
+/**
+ * hashmap_get() - gets value from hashmap from given key.
+ * @map: The hashmap to be looked up. Must no be NULL.
+ * @key: The key string. May be NULL.
+ *
+ * Return: The look up result, if the key-value pair entry
+ * exists, then returns its value's address, NULL otherwise.
+ */
+void *hashmap_get(hashmap_t *map, char *key)
+{
+    hashmap_node_t *node = hashmap_get_node(map, key);
+    return node ? node->val : NULL;
+}
+
 /**
  * hashmap_contains() - checks if the key-value pair entry exists
  * from given key.
@@ -351,7 +407,7 @@ void *hashmap_get(hashmap_t *map, char *key)
  */
 bool hashmap_contains(hashmap_t *map, char *key)
 {
-    return hashmap_get(map, key);
+    return hashmap_get_node(map, key);
 }
 
 /**