From 92cd6c46f410862466c143d96a3f577f2ede855f Mon Sep 17 00:00:00 2001
From: Jacob Janzen <jacob.a.s.janzen@gmail.com>
Date: Mon, 12 Feb 2024 21:43:52 -0600
Subject: use hash table for entity list

---
 ht.c | 185 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 185 insertions(+)
 create mode 100644 ht.c

(limited to 'ht.c')

diff --git a/ht.c b/ht.c
new file mode 100644
index 0000000..d23e141
--- /dev/null
+++ b/ht.c
@@ -0,0 +1,185 @@
+#include "ht.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define SIZE 1024
+
+struct node {
+    char        *key;
+    void        *val;
+    struct node *next;
+};
+
+struct hash_table {
+    struct node **vals;
+    int           max_size;
+    int           size;
+
+    int          curr_index;
+    struct node *curr_node;
+    bool         iterating;
+};
+
+static unsigned long djb2_hash(char *str)
+{
+    unsigned long hash = 5381;
+    int           c;
+
+    // hash * 33 + c
+    while ((c = *str++)) hash = ((hash << 5) + hash) + c;
+
+    return hash;
+}
+
+ht_t *ht_create(void)
+{
+    ht_t *h       = malloc(sizeof(ht_t));
+    h->max_size   = SIZE;
+    h->size       = 0;
+    h->vals       = malloc(sizeof(struct node) * h->max_size);
+    h->curr_index = 0;
+    h->curr_node  = NULL;
+    h->iterating  = false;
+
+    return h;
+}
+
+void ht_destroy(ht_t *h)
+{
+    // only destroy if h isn't NULL
+    if (h) {
+        // only destroy vals if it isn't NULL
+        if (h->vals) {
+            // iterate through the hash values
+            for (int i = 0; i < h->max_size; ++i) {
+                // iterate through the linked list and remove the value
+                struct node *curr = h->vals[i];
+                struct node *prev;
+                while (curr) {
+                    prev = curr;
+                    curr = curr->next;
+                    free(prev->key);
+                    free(prev);
+                }
+            }
+            free(h->vals);
+        }
+        free(h);
+    }
+}
+
+void *ht_find(ht_t *h, char *key)
+{
+    unsigned int hash = djb2_hash(key) % h->max_size;
+
+    // exit early if hash isn't in table
+    if (!h->vals[hash])
+        return NULL;
+
+    // iterate through values stored at `hash`; exit early if found
+    struct node *curr = h->vals[hash];
+    while (curr) {
+        if (strcmp(key, curr->key) == 0)
+            return curr->val;
+        curr = curr->next;
+    }
+
+    return NULL;
+}
+
+void ht_insert(ht_t *h, char *key, void *val)
+{
+    unsigned int hash = djb2_hash(key) % h->max_size;
+
+    // create a node
+    int len          = strlen(key);
+    struct node *new = malloc(sizeof(struct node));
+    new->key         = malloc(sizeof(char) * (len + 1));
+    for (int i = 0; i < len; ++i) {
+        new->key[i] = key[i];
+    }
+    new->key[len] = 0;
+    new->val      = val;
+
+    // insert node at beginning of list
+    if (h->vals[hash]) {
+        new->next = h->vals[hash];
+    }
+    h->vals[hash] = new;
+
+    ++(h->size);
+}
+
+void ht_delete(ht_t *h, char *key)
+{
+    unsigned int hash = djb2_hash(key) % h->max_size;
+
+    if (!h->vals[hash])
+        return; // exit if the hash is not found
+
+    // remove the key from the front of the list if it's there
+    if (strcmp(key, h->vals[hash]->key) == 0) {
+        struct node *temp = h->vals[hash];
+        h->vals[hash]     = h->vals[hash]->next;
+        free(temp->key);
+        free(temp);
+    } else {
+        // iterate through list and remove once a match is found
+        struct node *prev = h->vals[hash];
+        struct node *curr = h->vals[hash]->next;
+        while (curr) {
+            if (strcmp(key, curr->key) == 0) {
+                prev->next = curr->next;
+                free(curr->key);
+                free(curr);
+                return;
+            }
+
+            prev = curr;
+            curr = curr->next;
+        }
+    }
+}
+
+int ht_size(ht_t *h)
+{
+    return h->size;
+}
+
+void ht_iter_init(ht_t *h)
+{
+    h->curr_index = 0;
+    h->curr_node  = h->vals[0];
+}
+
+void *ht_iter_next(ht_t *h)
+{
+    // return NULL if we've reached the end
+    if (!h->curr_node && h->curr_index >= h->max_size)
+        return NULL;
+
+    if (!h->curr_node) {
+        // look for next index with node if current node is NULL
+        while (!h->curr_node) {
+            h->curr_node = h->vals[h->curr_index++];
+            if (h->curr_index >= h->max_size)
+                return NULL;
+        }
+        return h->curr_node->val;
+    } else {
+        // move to the next node
+        h->curr_node = h->curr_node->next;
+        if (h->curr_node)
+            return h->curr_node->val;
+
+        // look for next index with node if necessary
+        while (!h->curr_node) {
+            h->curr_node = h->vals[h->curr_index++];
+            if (h->curr_index >= h->max_size)
+                return NULL;
+        }
+        return h->curr_node->val;
+    }
+}
-- 
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