string hash code

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <ctype.h>
#include <string.h>

#define BUCKETS 100

struct s_stringMap;

typedef struct s_stringMap {
    const char *key;
    const char *value;
    struct s_stringMap *next;
} stringMap;

unsigned int hashmap( const char *s );
void hash_init( stringMap *map );
void hash_add( stringMap *map, const char *k, const char *v );
const char * hash_find(stringMap *map, const char *k);

unsigned int hashmap( const char *s )
{
    unsigned int hash = 0;

    if(!s || !*s) return 0;
    do {
        hash += *s;
        hash *= 13;
        s++;
    } while (*s);

    return hash % BUCKETS;
}

void hash_init( stringMap *map )
{
    int i;

    for(i = 0; i < BUCKETS; i++)
    {
        map[i].key = NULL;
        map[i].value = NULL;
        map[i].next = NULL;
    }
}

void hash_add( stringMap *map, const char *k, const char *v )
{
    unsigned int hashcode;
    stringMap *p;

    hashcode = hashmap(k);
    p = &map[hashcode];
    while(p->key && strcmp(p->key, k) && p->next)
        p = p->next;

    if(!p->key) {
        /* First node? */
        p->key = (const char *)strdup(k);
        p->value = (const char *)strdup(v);
        p->next = NULL;
    } else if(!strcmp(p->key, k)) {
        /* Found our match! */
        if(p->value)
            free((void *)p->value);
        p->value = (const char *)strdup(v);
    } else {
        /* New key */
        p->next = (stringMap *)calloc(1, sizeof(stringMap));
        p = p->next;
        p->key = (const char *)strdup(k);
        p->value = (const char *)strdup(v);
        p->next = NULL;
    }
}

const char * hash_find(stringMap *map, const char *k)
{
    unsigned int hashcode;
    stringMap *p;

    hashcode = hashmap(k);
    p = &map[hashcode];
    while(p->key && strcmp(p->key, k) && p->next)
        p = p->next;

    if(!p->key)
        return NULL;

    if(!strcmp(p->key, k))
        return p->value;

    return NULL;
}