intern.c

typedef struct intern_t {
    intern_t *next;
    uint32_t length; // can be narrower if you want to limit internable string length, which is a good idea.
    char str[1];
} intern_t;

hashtable_t string_table;

const char *string_intern(const char *str, uint32_t length) {
    uint64_t key = string_hash(str, length);
    intern_t *head = hashtable_get(string_table, key);
    for (intern_t *node = head; node; node = node->next) {
        if (length == node->length && strncmp(str, node->str, length) == 0)
            return node->str;
    }
    intern_t *new_head = malloc(sizeof(intern_t *) + sizeof(uint32_t) + length + 1);
    new_head->next = head;
    new_head->length = length;
    memcpy(new_head->str, str, length);
    new_head->str[length] = 0;
    hashtable_put(string_table, key, new_head);
    return new_head->str;
}