String Hash Table

#include <stdlib.h>
#include <assert.h>

#include "hash_table.h"
#include "types.h"

void hash_table_init(hash_table *ht) {
    ht->entries = (hash_table_entry*) calloc(INITIAL_HASH_TABLE_ENTRIES, sizeof(hash_table_entry));
    ht->num_entries = INITIAL_HASH_TABLE_ENTRIES;
    ht->used_entries = 0;
}

void hash_table_free(hash_table *ht) {
    free(ht->entries);
    free(ht);
}

void hash_table_put(hash_table *ht, char *key, void *value) {
    if(ht->used_entries == ht->num_entries) {
        hash_table_resize(ht);
    }

    s32 index = hash_table_find_index(ht, key);

    if(ht->entries[index].value) {
        index = hash_table_probe(ht, index);
    }

    assert(index != -1);

    if(value) {
        ht->used_entries++;
    } else {
        ht->used_entries--;
    }

    ht->entries[index].key = key;
    ht->entries[index].value = value;
}

void* hash_table_get(hash_table *ht, char *key) {
    s32 index = hash_table_find_index(ht, key);

    if(index == -1) {
        return 0;
    }

    return ht->entries[index].value;
}

void hash_table_resize(hash_table *ht) {
    u32 new_num_entries = ht->used_entries * 2;

    if(new_num_entries == 0) {
        new_num_entries = INITIAL_HASH_TABLE_ENTRIES;
    }

    hash_table_entry *old_entries = ht->entries;
    u32 old_num_entries = ht->num_entries;

    ht->entries = (hash_table_entry*) calloc(new_num_entries, sizeof(hash_table_entry));
    ht->num_entries = new_num_entries;
    ht->used_entries = 0;

    u32 index;
    for(index = 0; index < old_num_entries; index++) {
        hash_table_entry entry = old_entries[index];

        if(entry.value) {
            hash_table_put(ht, old_entries[index].key, old_entries[index].value);
        }
    }

    free(old_entries);
}

s32 hash_table_find_index(hash_table *ht, char *key) {
    return (s32) (hash_string(key) % ht->num_entries);
}

s32 hash_table_probe(hash_table *ht, s32 index) {
    do {
        index++;

        if(index >= ht->num_entries) {
            return -1;
        }
    } while(ht->entries[index].value);

    return index;
}

u64 hash_string(char *str) {
    if(!str) {
        return 0;
    }

    u64 hash = 5381;

    u8 c;
    while(c = *str++) {
        hash = ((hash << 5) + hash) + c;
    }

    return hash;
}