Hash tables indexed by atoms, to avoid expense of hashing keys on each

[mLib] / assoc.c

/* -*-c-*-
 *
 * $Id: assoc.c,v 1.1 2001/01/20 11:50:58 mdw Exp $
 *
 * Assocation tables
 *
 * (c) 2000 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * mLib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with mLib; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: assoc.c,v $
 * Revision 1.1  2001/01/20 11:50:58  mdw
 * Hash tables indexed by atoms, to avoid expense of hashing keys on each
 * lookup, and to reduce storage used by key texts.
 *
 */

/*----- Header files ------------------------------------------------------*/

#include "alloc.h"
#include "assoc.h"
#include "atom.h"
#include "hash.h"

/*----- Main code ---------------------------------------------------------*/

/* --- @assoc_create@ --- *
 *
 * Arguments:	@assoc_table *t@ = pointer to an association table
 *
 * Returns:	---
 *
 * Use:		Creates a new association table.
 */

void assoc_create(assoc_table *t)
{
  hash_create(&t->t, SYM_INITSZ);
  t->load = SYM_LIMIT(SYM_INITSZ);
}

/* --- @assoc_destroy@ --- *
 *
 * Arguments:	@assoc_table *t@ = pointer to an association table
 *
 * Returns:	---
 *
 * Use:		Destroys an association table.
 */

void assoc_destroy(assoc_table *t)
{
  hash_iter i;

  HASH_MKITER(&i, &t->t);
  for (;;) {
    hash_base *p;
    HASH_NEXT(&i, p);
    x_free(t->t.a, p);
  }
  hash_destroy(&t->t);
}

/* --- @assoc_find@ --- *
 *
 * Arguments:	@assoc_table *t@ = pointer to an association table
 *		@atom *a@ = an atom to label the item
 *		@size_t sz@ = size of block to allocate
 *		@unsigned *f@ = pointer to `found' flag
 *
 * Returns:	A pointer to the item located or null.
 *
 * Use:		Looks up an atom in an association table.  If the atom is
 *		found, the association is returned.  If not, and @sz@ is
 *		zero, a null pointer is returned.  Otherwise, a block of size
 *		@sz@ is allocated, its @assoc_base@ header is filled in, and
 *		the pointer returned.  The flag @*f@ is cleared if the item
 *		couldn't be found, or set if it was.
 *
 *		All the atoms used in a particular table should 
 */

void *assoc_find(assoc_table *t, atom *a, size_t sz, unsigned *f)
{
  hash_base **bin = HASH_BIN(&t->t, a->b.b.hash), **p;
  assoc_base *q;

  /* --- Try to find the association --- */

  for (p = bin; *p; p = &(*p)->next) {
    q = (assoc_base *)*p;
    if (q->a == a) {
      *p = q->b.next;
      q->b.next = *bin;
      *bin = &q->b;
      if (f) *f = 1;
      return (q);
    }
  }

  /* --- Failed to find a match --- */

  if (f) *f = 0;
  if (!sz) return (0);

  /* --- Make a new assoication --- */

  q = x_alloc(t->t.a, sz);
  q->b.next = *bin;
  q->b.hash = ATOM_HASH(a);
  *bin = &q->b;

  /* --- Maybe extend the table --- */

  if (t->load)
    t->load--;
  if (!t->load && hash_extend(&t->t))
    t->load = SYM_LIMIT(t->t.mask + 1);
  return (q);
}

/* --- @assoc_remove@ --- *
 *
 * Arguments:	@assoc_table *t@ = pointer to an association table
 *		@void *p@ = pointer to a block to remove
 *
 * Returns:	---
 *
 * Use:		Removes an association from a table.
 */

void assoc_remove(assoc_table *t, void *p)
{
  assoc_base *q = p;
  hash_remove(&t->t, &q->b);
  x_free(t->t.a, q);
  t->load++;
}

/* --- @assoc_mkiter@, @assoc_next@ --- *
 *
 * Arguments:	@assoc_iter *i@ = pointer to an iterator
 *		@assoc_table *t@ = pointer to an association table
 *
 * Returns:	Next association, or null, for @assoc_next@; nothing for
 *		@assoc_mkiter@.
 *
 * Use:		Iterates over the associations in a table.
 */

void assoc_mkiter(assoc_iter *i, assoc_table *t) { ASSOC_MKITER(i, t); }
void *assoc_next(assoc_iter *i) { void *p; ASSOC_NEXT(i, p); return (p); }

/*----- That's all, folks -------------------------------------------------*/