diff --git a/src/database.c b/src/database.c
index ced3cbe..cc9bc7f 100644
--- a/src/database.c
+++ b/src/database.c
@@ -41,20 +41,25 @@ void database_load(
     char *file_buf;
 
     trie_root_init(&database_out->trie_root);
+    /* Initializes movies to capacity 2003. */
     movies_init(&database_out->movies, 2003, error);
 
     if (error->code == error_none) {
+        /* Initializes users to capacity 2003. */
         users_init(&database_out->users, 2003, error);
     }
 
     if (error->code == error_none) {
+        /* Initializes tags to capacity 2003. */
         tags_init(&database_out->tags, 2003, error);
     }
 
     if (error->code == error_none) {
+        /* Allocates the buffer for file buffering. */
         file_buf = moviedb_alloc(IO_BUF_SIZE, error);
     }
 
+    /* Actually loads everything, if no error. */
     if (error->code == error_none)  {
         load_movies(database_out, buf, file_buf, error);
 
@@ -96,6 +101,7 @@ static void load_movies(
         input_file_setbuf(file, file_buf, IO_BUF_SIZE, error);
 
         if (error->code == error_none) {
+            /* Initializes the CSV parser. */
             movie_parser_init(&parser, file, buf, error);
         }
 
@@ -103,15 +109,25 @@ static void load_movies(
         while (has_data) {
             has_data = movie_row_parse(&parser, buf, &row, error);
             if (has_data) {
+                /* Inserts into the trie. */
                 trie_insert(&database->trie_root, row.title, row.id, error);
 
                 if (error->code == error_dup_movie_title) {
+                    /* Ignore duplicated movie title error. */
                     error_set_code(error, error_none);
                 }
+
                 if (error->code == error_none) {
+                    /* Inserts into the movie table. */
                     movies_insert(&database->movies, &row, error);
                 } 
                 if (error->code != error_none) {
+                    /*
+                     * Destroys the row memory if an error happens.
+                     *
+                     * Normally, movie table would get the ownership of the
+                     * heap-allocated fields of the row.
+                     */
                     movie_row_destroy(&row);
                 }
 
@@ -147,6 +163,7 @@ static void load_ratings(
         input_file_setbuf(file, file_buf, IO_BUF_SIZE, error);
 
         if (error->code == error_none) {
+            /* Initializes the CSV parser. */
             rating_parser_init(&parser, file, buf, error);
         }
 
@@ -155,9 +172,11 @@ static void load_ratings(
             has_data = rating_row_parse(&parser, buf, &row, error);
 
             if (has_data) {
+                /* Inserts into the user table. */
                 users_insert_rating(&database->users, &row, error);
 
                 if (error->code == error_none) {
+                    /* Adds this rating to the respective movie. */
                     movies_add_rating(
                             &database->movies,
                             row.movieid,
@@ -195,6 +214,7 @@ static void load_tags(
         input_file_setbuf(file, file_buf, IO_BUF_SIZE, error);
 
         if (error->code == error_none) {
+            /* Initializes the CSV parser. */
             tag_parser_init(&parser, file, buf, error);
         }
 
@@ -203,8 +223,10 @@ static void load_tags(
             has_data = tag_row_parse(&parser, buf, &row, error);
 
             if (has_data) {
+                /* Inserts into the tag table. */
                 tags_insert(&database->tags, &row, error);
                 if (error->code == error_dup_movie_id) {
+                    /* Ignore duplicated movie ID error. */
                     error_set_code(error, error_none);
                 }
                 has_data = error->code == error_none;
diff --git a/src/hash.c b/src/hash.c
index bc5b43d..88b6a9d 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -36,11 +36,16 @@ moviedb_hash_t moviedb_hash_str(char const *restrict string)
 
     while (string[index] != 0) {
         curr = (unsigned char) string[index];
+        /* Multiplication of previous state by large prime. */
         hash *= 0xC3FB39E53E91D33F;
+        /* XOR with multiplication of current element by prime. */
         hash ^= curr * 0x1A3C2A17EE36142B;
+        /* Marks the index. */
+        hash += index;
         index++;
     }
 
+    /* Marks the key length. */
     hash ^= moviedb_hash_uint64(index);
 
     return hash;
diff --git a/src/id.c b/src/id.c
index 4fa9c27..50bd67b 100644
--- a/src/id.c
+++ b/src/id.c
@@ -12,6 +12,7 @@ moviedb_id_t moviedb_id_parse(
 
     while (string[i] != 0 && error->code == error_none) {
         if (id * 10 >= id && string[i] >= '0' && string[i] <= '9') {
+            /* Accounts the digit. */
             id *= 10;
             id += string[i] - '0';
             i++;
@@ -19,6 +20,7 @@ moviedb_id_t moviedb_id_parse(
             if (error->code == error_none) {
                 error_string = moviedb_alloc(strlen(string) + 1, error);
                 if (error->code == error_none) {
+                    /* Copies the input string to an error. */
                     strcpy(error_string, string);
                     error_set_code(error, error_id);
                     error->data.id.has_line = false;
@@ -29,6 +31,7 @@ moviedb_id_t moviedb_id_parse(
         }
     }
 
+    /* Empty string is an error. */
     if (i == 0 && error->code == error_none) {
         error_set_code(error, error_id);
         error->data.id.has_line = false;
@@ -50,6 +53,7 @@ size_t moviedb_id_to_str(
         start--;
         buffer[start] = 0;
 
+        /* Write the number digits starting backwards. */
         do {
             if (start > 0) {
                 start--;