SRC/hash.c

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#include <stdlib.h>
#include <string.h>
#include "hash.h"
#include "util.h"

#define HASHSIZE 4093

static int hash_value(char *name);



struct s_hash **
alloc_hash_table(void)
{

/* Creates a hash table with HASHSIZE different locations (hash values).   */

    struct s_hash **hash_table;

    hash_table = (struct s_hash **)my_calloc(sizeof(struct s_hash *),
                                             HASHSIZE);
    return (hash_table);
}


void
free_hash_table(struct s_hash **hash_table)
{

/* Frees all the storage associated with a hash table. */

    int i;
    struct s_hash *h_ptr, *temp_ptr;

    for(i = 0; i < HASHSIZE; i++)
        {
            h_ptr = hash_table[i];
            while(h_ptr != NULL)
                {
                    free(h_ptr->name);
                    temp_ptr = h_ptr->next;
                    free(h_ptr);
                    h_ptr = temp_ptr;
                }
        }

    free(hash_table);
}


struct s_hash_iterator
start_hash_table_iterator(void)
{

/* Call this routine before you start going through all the elements in    *
 * a hash table.  It sets the internal indices to the start of the table.  */

    struct s_hash_iterator hash_iterator;

    hash_iterator.i = -1;
    hash_iterator.h_ptr = NULL;
    return (hash_iterator);
}


struct s_hash *
get_next_hash(struct s_hash **hash_table,
              struct s_hash_iterator *hash_iterator)
{

/* Returns the next occupied hash entry, and moves the iterator structure    *
 * forward so the next call gets the next entry.                             */

    int i;
    struct s_hash *h_ptr;

    i = hash_iterator->i;
    h_ptr = hash_iterator->h_ptr;

    while(h_ptr == NULL)
        {
            i++;
            if(i >= HASHSIZE)
                return (NULL);  /* End of table */

            h_ptr = hash_table[i];
        }

    hash_iterator->h_ptr = h_ptr->next;
    hash_iterator->i = i;
    return (h_ptr);
}


struct s_hash *
insert_in_hash_table(struct s_hash **hash_table,
                     char *name,
                     int next_free_index)
{

/* Adds the string pointed to by name to the hash table, and returns the    *
 * hash structure created or updated.  If name is already in the hash table *
 * the count member of that hash element is incremented.  Otherwise a new   *
 * hash entry with a count of zero and an index of next_free_index is       *
 * created.                                                                 */

    int i;
    struct s_hash *h_ptr, *prev_ptr;

    i = hash_value(name);
    prev_ptr = NULL;
    h_ptr = hash_table[i];

    while(h_ptr != NULL)
        {
            if(strcmp(h_ptr->name, name) == 0)
                {
                    h_ptr->count++;
                    return (h_ptr);
                }

            prev_ptr = h_ptr;
            h_ptr = h_ptr->next;
        }

/* Name string wasn't in the hash table.  Add it. */

    h_ptr = (struct s_hash *)my_malloc(sizeof(struct s_hash));
    if(prev_ptr == NULL)
        {
            hash_table[i] = h_ptr;
        }
    else
        {
            prev_ptr->next = h_ptr;
        }
    h_ptr->next = NULL;
    h_ptr->index = next_free_index;
    h_ptr->count = 1;
    h_ptr->name = (char *)my_malloc((strlen(name) + 1) * sizeof(char));
    strcpy(h_ptr->name, name);
    return (h_ptr);
}


struct s_hash *
get_hash_entry(struct s_hash **hash_table,
               char *name)
{

/* Returns the hash entry with this name, or NULL if there is no            *
 * corresponding entry.                                                     */

    int i;
    struct s_hash *h_ptr;

    i = hash_value(name);
    h_ptr = hash_table[i];

    while(h_ptr != NULL)
        {
            if(strcmp(h_ptr->name, name) == 0)
                return (h_ptr);

            h_ptr = h_ptr->next;
        }

    return (NULL);
}


static int
hash_value(char *name)
{

/* Creates a hash key from a character string.  Only the first character and *
 * the last 8 characters of the string are used -- that may be dumb.         */

    int i, k;
    int val = 0, mult = 1;

    i = strlen(name);
    k = max(i - 8, 0);
    for(i = strlen(name) - 1; i >= k; i--)
        {
            val += mult * ((int)name[i]);
            mult *= 7;
        }
    val += (int)name[0];
    val %= HASHSIZE;
    return (val);
}

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