a simple hash table implementation

debug.h

#ifndef _DEBUG_H
#define _DEBUG_H

#ifdef DEBUG

#include<stdio.h>

#define INFO(format) fprintf(stderr,"%s:%d:%s -> " format "\n", __FILE__, __LINE__, __func__)
#define LOG(format, ...) fprintf(stderr,"%s:%d:%s -> " format "\n", __FILE__, __LINE__, __func__, __VA_ARGS__)

#else

#define LOG(...)
#define INFO(...)

#endif // debug

#endif // debug.h

hashtable.c

/**
* License GPLv3+
* @file hashtable.c
* @brief a simple hash table implementation
* @author Ankur Shrivastava
*/
#include "hashtable.h"
#include "debug.h"

#include <stdlib.h>
#include <string.h>

// element operations
/**
* Function to create a now hash_table element
* @returns hash_table_element_t object when success
* @returns NULL when no memory
*/
hash_table_element_t * hash_table_element_new()
{
    INFO("creating a new hash table element");
    return calloc(1, hash_table_element_s);
}

/**
* Function to delete an hash table element
* @param table table from which element has to be deleted
* @param element hash table element to be deleted
*/
void hash_table_element_delete(hash_table_t * table, hash_table_element_t * element)
{
    INFO("Deleting an hash table element");
    if (table->mode == MODE_COPY)
    {
        free(element->value);
    }
    free(element->key);
    free(element);
}

// hash table operations
/**
* Fuction to create a new hash table
* @param mode hash_table_mode which the hash table should follow
* @returns hash_table_t object which references the hash table
* @returns NULL when no memory
*/
hash_table_t * hash_table_new(hash_table_mode_t mode)
{
    INFO("Creating a new hash table");
    hash_table_t *table = calloc(1, hash_table_s);
    table->mode = mode;
    return table;
}

/**
* Function to delete the hash table
* @param table hash table to be deleted
*/
void hash_table_delete(hash_table_t * table)
{
    INFO("Deleating a hash table");
    size_t i=0;
    for (;i<HASH_LEN;i++)
    {
        while (table->store_house[i])
        {
            hash_table_element_t * temp = table->store_house[i];
            table->store_house[i] = table->store_house[i]->next;
            hash_table_element_delete(table, temp);
        }
    }
    free(table);
}

/**
* Function to add a key - value pair to the hash table, use HT_ADD macro
* @param table hash table to add element to
* @param key pointer to the key for the hash table
* @param key_len length of the key in bytes
* @param value pointer to the value to be added against the key
* @param value_len length of the value in bytes
* @returns 0 on sucess
* @returns -1 when no memory
*/
int hash_table_add(hash_table_t * table, void * key, size_t key_len, void * value, size_t value_len)
{
    size_t hash = HASH(key, key_len);
    hash_table_element_t * element = hash_table_element_new();
    if (!element)
    {
        INFO("Cannot allocate memory for element");
        return -1; // No Memory
    }
    if (table->mode == MODE_COPY)
    {
        LOG("Adding a key-value pair to the hash table with hash -> %d, in COPY MODE", (int)hash);
        element->key = malloc(key_len);
        element->value = malloc(value_len);
        if (element->key && element->value)
        {
            memcpy(element->key, key, key_len);
            memcpy(element->value, value, value_len);
        }
        else
        {
            if (element->key)
            {
                free(element->key);
                INFO("Cannot allocate memory for value");
            }
            if (element->value)
            {
                free(element->value);
                INFO("Cannot allocate memory for key");
            }
            free(element);
            return -1; //No Memory
        }
    }
    else if (table->mode == MODE_VALUEREF)
    {
        LOG("Adding a key-value pair to the hash table with hash -> %d, in VALUEREF MODE", (int)hash);
        element->key = malloc(key_len);
        if (element->key)
        {
            memcpy(element->key, key, key_len);
        }
        else
        {
            INFO("Cannot allocate memory for key");
            free(element);
            return -1; //No Memory
        }
        element->value = value;
    }
    element->key_len = key_len;
    element->value_len = value_len;
    element->next = NULL;
    // find the key position for chaining
    if (!table->store_house[hash])
    {
        LOG("No Conflicts adding the first element at %d", (int)hash);
        table->store_house[hash] = element;
        table->key_count++;
    }
    else
    {
        LOG("Conflicts adding element at %d", (int)hash);
        hash_table_element_t * temp = table->store_house[hash];
        while(temp->next)
        {
            while(temp->next && temp->next->key_len!=key_len)
            {
                temp = temp->next;
            }
            if(temp->next)
            {
                if (!memcmp(temp->next->key, key, key_len))
                {
                    LOG("Found Key at hash -> %d", (int)hash);
                    hash_table_element_t *to_delete = temp->next;
                    temp->next = element;
                    element->next = to_delete->next;
                    hash_table_element_delete(table, to_delete);
                    // since we are replacing values no need to change key_count
                    return 0;
                }
                else
                {
                    temp = temp->next;
                }
            }
        }
        temp->next = element;
        table->key_count++;
    }
    return 0;
}

/**
* Function to remove an hash table element (for a given key) from a given hash table
* @param table hash table from which element has to be removed
* @param key pointer to the key which has to be removed
* @param key_len size of the key in bytes
* @returns 0 on sucess
* @returns -1 when key is not found
*/
int hash_table_remove(hash_table_t * table, void * key, size_t key_len)
{
    INFO("Deleting a key-value pair from the hash table");
    size_t hash = HASH(key, key_len);
    if (!table->store_house[hash])
    {
        LOG("Key Not Found -> No element at %d", (int)hash);
        return -1; // key not found
    }
    hash_table_element_t *temp = table->store_house[hash];
    hash_table_element_t *prev = temp;
    while(temp)
    {
        while(temp && temp->key_len!=key_len)
        {
            prev = temp;
            temp = temp->next;
        }
        if(temp)
        {
            if (!memcmp(temp->key, key, key_len))
            {
                if (prev == table->store_house[hash])
                {
                    table->store_house[hash] = temp->next;
                }
                else
                {
                    prev->next = temp->next;
                }
                hash_table_element_delete(table, temp);
                INFO("Deleted a key-value pair from the hash table");
                table->key_count--;
                return 0;
            }
            temp=temp->next;
        }
    }
    INFO("Key Not Found");
    return -1; // key not found
}

/**
* Function to lookup a key in a particular table
* @param table table to look key in
* @param key pointer to key to be looked for
* @param key_len size of the key to be searched
* @returns NULL when key is not found in the hash table
* @returns void* pointer to the value in the table
*/
void * hash_table_lookup(hash_table_t * table, void * key, size_t key_len)
{
    size_t hash = HASH(key, key_len);
    LOG("Looking up a key-value pair for hash -> %d", (int)hash);
    if (!table->store_house[hash])
    {
        LOG("Key not found at hash %d, no entries", (int)hash);
        return NULL; // key not found
    }
    hash_table_element_t *temp = table->store_house[hash];
    while(temp)
    {
        while(temp && temp->key_len!=key_len)
        {
            temp = temp->next;
        }
        if(temp)
        {
            if (!memcmp(temp->key, key, key_len))
            {
                LOG("Found Key at hash -> %d", (int)hash);
                return temp->value;
            }
            else
            {
                temp = temp->next;
            }
        }
    }
    LOG("Key not found at hash %d", (int)hash);
    return NULL; // key not found
}

/**
* Function to look if the exists in the hash table
* @param key pointer to key to be looked for
* @param key_len size of the key to be searched
* @returns 0 when key is not found
* @returns 1 when key is found
*/
int hash_table_has_key(hash_table_t * table, void * key, size_t key_len)
{
    size_t hash = HASH(key, key_len);
    LOG("Searching for key with hash -> %d", (int)hash);
    if (!table->store_house[hash])
    {
        LOG("Key not found with hash -> %d, no entries", (int)hash);
        return 0; // key not found
    }
    hash_table_element_t *temp = table->store_house[hash];
    while(temp)
    {
        while(temp && temp->key_len!=key_len)
        {
            temp = temp->next;
        }
        if(temp)
        {
            if (!memcmp(temp->key, key, key_len))
            {
                LOG("Key Found with hash -> %d", (int)hash);
                return 1; // key found
            }
            temp=temp->next;
        }
    }
    LOG("Key not found with hash -> %d", (int)hash);
    return 0; // key not found
}

/**
* Function to return all the keys in a given hash table
* @param table hash table from which key are to be reterived
* @param keys a void** pointer where keys are filled in (memory allocated internally and must be freed)
* @return total number of keys filled in keys
*/
int hash_table_get_keys(hash_table_t * table, void ** keys)
{
    size_t i = 0;
    size_t count = 0;
    keys = calloc(table->key_count, sizeof(void *));
    for(i=0;i<HASH_LEN;i++)
    {
        if (table->store_house[i])
        {
            keys[count++] = table->store_house[i];
            hash_table_element_t *temp = table->store_house[i];
#ifdef DEBUG
            size_t num = 1;
#endif
            while(temp->next)
            {
                keys[count++] = temp->next;
                temp = temp->next;
#ifdef DEBUG
                num++;
#endif
            }
#ifdef DEBUG
            LOG("found %d key(s) at hash -> %d", (int)num, (int)i);
#endif
        }
    }
    return count;
}

/**
* Function that returns a hash value for a given key and key_len
* @param key pointer to the key
* @param key_len length of the key
* @param max_key max value of the hash to be returned by the function
* @returns hash value belonging to [0, max_key)
*/
uint16_t hash_table_do_hash(void * key, size_t key_len, uint16_t max_key)
{
    uint16_t *ptr = (uint16_t *) key;
    uint16_t hash = 0xbabe; // WHY NOT
    unsigned int i=0;
    for(;i<(key_len/2);i++)
    {
        hash+=(i<<4 ^ *ptr<<8 ^ *ptr);
        ptr++;
    }
    hash = hash / max_key;
    return hash;
}

hashtable.h

/**
 * License GPLv3+
 * @file hashtable.h
 * @brief a simple hash table implementation
 * @author Ankur Shrivastava
 */
#ifndef _HASHTABLE_H
#define _HASHTABLE_H

#include<sys/types.h>
#include<stdint.h>

#define HASH_LEN 256
#define HASH1(x,y) (size_t)(((*(int *)x)+(int)y)%HASH_LEN)
#define HASH(x,y) hash_table_do_hash(x,y,HASH_LEN)

// forward declaration
typedef struct hash_table_element hash_table_element_t;

/**
 * @struct hash_table_element "hashtable.h"
 * @brief stores an hash table element for use in the hash table
 */
struct hash_table_element
{
    /**
     * store the length in bytes of the key
     */
    size_t key_len;
    /**
     * stores the length in bytes of the key (only for copy mode)
     */
    size_t value_len;
    /**
     * pointer to the key 
     */
    void * key;
    /**
     * pointer to the value
     */
    void * value;
    /**
     * next chained key for this hash
     */
    hash_table_element_t * next;
};
#define hash_table_element_s sizeof(hash_table_element_t)

/**
 * @enum hash_table_mode defines the mode of operation of hash table
 */
typedef enum hash_table_mode{
    /** copy mode here values as well as key is copied */
    MODE_COPY,
    /** value reference mode, here ONLY key is copies and value is always referred*/
    MODE_VALUEREF
} hash_table_mode_t;

/**
 * @struct hash_table "hashtable.h"
 * @brief identifies the hashtable for which operations are to be performed
 */
typedef struct hash_table
{
    /**
     * the hash table array where all values are stored
     */
    hash_table_element_t  * store_house[HASH_LEN];
    /**
     * mode of the hash table
     */
    hash_table_mode_t mode;
    /**
     * number of keys in the hash table
     */
    size_t key_count;
} hash_table_t;
#define hash_table_s sizeof(hash_table_t)


// element operations
/**
 * Function to create a now hash_table element
 * @returns hash_table_element_t object when success
 * @returns NULL when no memory
 */
hash_table_element_t * hash_table_element_new();

/**
 * Function to delete an hash table element
 * @param table table from which element has to be deleted
 * @param element hash table element to be deleted
 */
void hash_table_element_delete(hash_table_t *, hash_table_element_t *);

/**
 * Function that returns a hash value for a given key and key_len
 * @param key pointer to the key
 * @param key_len length of the key
 * @param max_key max value of the hash to be returned by the function 
 * @returns hash value belonging to [0, max_key)
 */
uint16_t hash_table_do_hash(void * key, size_t key_len, uint16_t max_key);

// hash table operations
/**
 * Fuction to create a new hash table
 * @param mode hash_table_mode which the hash table should follow
 * @returns hash_table_t object which references the hash table
 * @returns NULL when no memory
 */
hash_table_t * hash_table_new(hash_table_mode_t);

/**
 * Function to delete the hash table
 * @param table hash table to be deleted
 */
void hash_table_delete(hash_table_t *);

/**
 * macro to add a key - value pair to the hash table
 * @note use this macro when size of key and/or value can be given by sizeof
 * @param table hash table to add element to
 * @param key pointer to the key for the hash table
 * @param value pointer to the value to be added against the key
 * @returns 0 on sucess
 * @returns -1 when no memory
 */
#define HT_ADD(table, key, value) hash_table_add(table, (void *) key, sizeof(*key), (void *) value, sizeof(*value))

/**
 * Function to add a key - value pair to the hash table, use HT_ADD macro
 * @param table hash table to add element to
 * @param key pointer to the key for the hash table
 * @param key_len length of the key in bytes
 * @param value pointer to the value to be added against the key
 * @param value_len length of the value in bytes
 * @returns 0 on sucess
 * @returns -1 when no memory
 */
int hash_table_add(hash_table_t *, void *, size_t, void *, size_t);

/**
 * macro to remove an hash table element (for a given key) from a given hash table
 * @note use this macro when size of key and/or value can be given by sizeof
 * @param table hash table from which element has to be removed
 * @param key pointer to the key which has to be removed
 * @returns 0 on sucess
 * @returns -1 when key is not found
 */
#define HT_REMOVE(table, key) hash_table_remove(table, key, sizeof(*key))

/**
 * Function to remove an hash table element (for a given key) from a given hash table
 * @param table hash table from which element has to be removed
 * @param key pointer to the key which has to be removed
 * @param key_len size of the key in bytes
 * @returns 0 on sucess
 * @returns -1 when key is not found
 */
int hash_table_remove(hash_table_t *, void *, size_t);

/**
 * macro to lookup a key in a particular table
 * @param table table to look key in
 * @param key pointer to key to be looked for
 * @returns NULL when key is not found in the hash table
 * @returns void* pointer to the value in the table
 */
#define HT_LOOKUP(table, key) hash_table_lookup(table, key, sizeof(*key))

/**
 * Function to lookup a key in a particular table
 * @note use this macro when size of key and/or value can be given by sizeof
 * @param table table to look key in
 * @param key pointer to key to be looked for
 * @param key_len size of the key to be searched
 * @returns NULL when key is not found in the hash table
 * @returns void* pointer to the value in the table
 */
void * hash_table_lookup(hash_table_t *, void *, size_t);

/**
 * macro to look if the exists in the hash table
 * @note use this macro when size of key and/or value can be given by sizeof
 * @param key pointer to key to be looked for
 * @returns 0 when key is not found
 * @returns 1 when key is found
 */
#define HT_HAS_KEY(table, key) hash_table_has_key(table, key, sizeof(*key))

/**
 * Function to look if the exists in the hash table
 * @param key pointer to key to be looked for
 * @param key_len size of the key to be searched
 * @returns 0 when key is not found
 * @returns 1 when key is found
 */
int hash_table_has_key(hash_table_t *, void *, size_t);

/**
 * Function to return all the keys in a given hash table
 * @param table hash table from which key are to be reterived
 * @param keys a void** pointer where keys are filled in (memory allocated internally and must be freed)
 * @return total number of keys filled in keys 
 */
int hash_table_get_keys(hash_table_t *, void **);

#endif

main.c

#include<stdio.h>
#include "hashtable.h"

int main()
{
    hash_table_t *table = hash_table_new(MODE_VALUEREF);
    int i = 1;
    int val = 100;
    int val2 = 200;
    int j = 2;
    int x =0;
    for (x=0;x<300;x++)
    {
        // use the macro
        HT_ADD(table, &j, &val);
        // or use the function
        //hash_table_add(table, &j, i, (void *) &val, sizeof(int));
        val++;
        j++;
    }
    hash_table_add(table, &j, i, (void *) &val2, 1);
    j--; j--;
    hash_table_remove(table, &j, i);
    HT_REMOVE(table, &j);
    if (hash_table_has_key(table, &j, i))
    {
        printf("Key found %d\n", j);
    }
    else
    {
        printf("Key NOT found %d\n", j);
    }
    val = -100;
    val2 = -200;
    int *value = NULL;
    value = (int* ) HT_LOOKUP(table, &j);
    void** keys = NULL;
    size_t num = hash_table_get_keys(table, keys);
    printf("found %d keys\n", (int)num);
    printf("j -> %d \n", j);
    if (value)
        printf("value is %d\n", *value);
    else
        printf("*value is %p\n", value);

    return 0;
}

Makefile

CC = gcc -fPIC 
LDFLAGS = -lm

# set DEBUG options
ifdef DEBUG
CFLAGS = -Wall -Wextra -ggdb -pg -DDEBUG
else
CFLAGS = -Wall -O2
endif

#name all the object files
OBJS = main.o hashtable.o

all : hashtable

hashtable : $(OBJS)
	$(CC) $(LDFLAGS) -o main $^

debug :
	make all DEBUG=1

%.o : %.c
	$(CC) $(CFLAGS) -o $@ -c $^

doxy :
	doxygen Doxyfile

clean :
	rm -rf $(OBJS) main