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/*                      Atoms: Names to numbers                 HTAtom.c
**                      =======================
**
**      Atoms are names which are given representative pointer values
**      so that they can be stored more efficiently, and comparisons
**      for equality done more efficiently.
**
**      Atoms are kept in a hash table consisting of an array of linked lists.
**
** Authors:
**      TBL     Tim Berners-Lee, WorldWideWeb project, CERN
**      (c) Copyright CERN 1991 - See Copyright.html
**
*/

#define HASH_SIZE       101             /* Tunable */
#include "HTUtils.h"
#include "HTAtom.h"

#ifdef ERWISE
#include <stdio.h>
#endif

PRIVATE HTAtom * hash_table[HASH_SIZE];
PRIVATE BOOL initialised = NO;

#ifdef __STDC__
PUBLIC HTAtom * HTAtom_for(const char * string)
#else
PUBLIC HTAtom * HTAtom_for(string)
    char * string;
#endif
{
    int hash;
    CONST char * p;
    HTAtom * a;
   
    /*          First time around, clear hash table
    */

    if (!initialised) {
        int i;
        for (i=0; i<HASH_SIZE; i++)
            hash_table[i] = (HTAtom *) 0;
        initialised = YES;
    }
   
    /*          Generate hash function
    */

    for(p=string, hash=0; *p; p++) {
        hash = (hash * 3 + *p) % HASH_SIZE;
    }
   
    /*          Search for the string in the list
    */

    for (a=hash_table[hash]; a; a=a->next) {
        if (0==strcmp(a->name, string)) {
            if (TRACE) printf("HTAtom: Old atom %d for `&s'\n", a, string);
            return a;                           /* Found: return it */
        }
    }
   
    /*          Generate a new entry
    */

    a = (HTAtom *)malloc(sizeof(*a));
    if (a == NULL) outofmem(__FILE__, "HTAtom_for");
    a->name = (char *)malloc(strlen(string)+1);
    if (a->name == NULL) outofmem(__FILE__, "HTAtom_for");
    strcpy(a->name, string);
    a->next = hash_table[hash];         /* Put onto the head of list */
    hash_table[hash] = a;
    if (TRACE) printf("HTAtom: New atom %d for `&s'\n", a, string);
    return a;
}