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lrpo.c

/*
 *  lrpo.c -- Lexicograpphic recursive path ordering (RPO with status)
 *
 */

#include "header.h"

/*************
 *
 *    int sym_precedence(sym_num_1, sym_num_2)
 *
 *    Return SAME_AS, GREATER_THAN, LESS_THAN, or NOT_COMPARABLE.
 *
 *************/

static int sym_precedence(int sym_num_1,
                    int sym_num_2)
{
  int p1, p2, sn;
  static int warning_given;

  if (sym_num_1 == sym_num_2)
    return(SAME_AS);
  else {
    p1 = sn_to_node(sym_num_1)->lex_val;
    p2 = sn_to_node(sym_num_2)->lex_val;
      
    if (p1 == MAX_INT || p2 == MAX_INT) {
      if (!warning_given) {
      sn = (p1 == MAX_INT ? sym_num_1 : sym_num_2);
      fprintf(stderr, "%c\nWARNING: at least one symbol, %s, is not lexically comparable.\nIf you use a lex command, you should include all symbols that\nwill be compared.  This warning will not be given again.\n", Bell, sn_to_str(sn));
      warning_given = 1;
      }
      return(NOT_COMPARABLE);
    }
    else if (p1 > p2)
      return(GREATER_THAN);
    else if (p1 < p2)
      return(LESS_THAN);
    else
      return(SAME_AS);
  }
}  /* sym_precedence */

/*************
 *
 *    int lrpo_status(sym_num)
 *
 *************/

static int lrpo_status(int sym_num)
{

  return(sn_to_node(sym_num)->lex_rpo_status);

}  /* lrpo_status */

/*************
 *
 *    int lrpo_lex(t1, t2) -- Is t1 > t2 ?
 *
 *    t1 and t2 have same functor and the functor has lr status.
 *    (If a functor really has rl status, its args have already been
 *    reversed.  This is true of all subterms of t1 and t2.)
 *
 *************/

static int lrpo_lex(struct term *t1,
                struct term *t2)
{
  struct rel *r1, *r2;
  int rc;

  /* First skip over any identical arguments. */
  /* (Same number of args, because same functor.) */

  for (r1 = t1->farg, r2 = t2->farg;
       r1 && term_ident(r1->argval, r2->argval);
       r1 = r1->narg, r2 = r2->narg) /* empty body */ ;

  if (!r1)
    rc = 0;  /* t1 and t2 identical */
  else if (lrpo(r1->argval, r2->argval)) {
    /* return (t1 > each remaining arg of t2) */
    for (r2 = r2->narg; r2 && lrpo(t1, r2->argval); r2 = r2->narg)
      /* empty body */ ;
    rc = (r2 == NULL);
  }
  else {
    /* return (there is a remaining arg of t1 s.t. arg == t2 or arg > t2) */
    rc = 0;
    for (r1 = r1->narg; r1; r1 = r1->narg) {
      if (term_ident(r1->argval, t2) || lrpo(r1->argval, t2))
      rc = 1;
    }
  }

  return(rc);

}  /* lrpo_lex */

/*************
 *
 *    int num_occurrences(t_arg, t) -- How many times does t_arg occur
 *    as an argument of t?
 *
 *************/

static int num_occurrences(struct term *t_arg,
                     struct term *t)
{
  struct rel *r;
  int i;

  for (i = 0, r = t->farg; r; r = r->narg)
    if (term_ident(r->argval, t_arg))
      i++;

  return(i);

}  /* num_occurrences */

/*************
 *
 *   struct term *set_multiset_diff(t1, t2)
 *
 *   Construct the multiset difference, then return the set of that.
 *   Result must be deallocated by caller with zap_term.
 *
 *   In other words, viewing a term as a multiset of its arguments,
 *   find the set of t1's arguments that have more occurrences in
 *   t1 than in t2.
 *
 *************/

static struct term *set_multiset_diff(struct term *t1,
                              struct term *t2)
{
  struct term *t_result;
  struct rel *prev, *curr, *r1, *r;
  int i;

  t_result = get_term();
  prev = NULL;
  i = 0;
  for (r1 = t1->farg; r1; r1 = r1->narg) {
    /* First check if a preceeding occurrence of this arg has */
    /* already been done. */

    for (r = t1->farg; r != r1 && term_ident(r->argval, r1->argval) == 0; r = r->narg)
      /* empty body */ ;

    if (r == r1 && num_occurrences(r1->argval, t1) > num_occurrences(r1->argval, t2)) {
      i++;
      curr = get_rel();
      curr->argval = copy_term(r1->argval);
      if (!prev)
      t_result->farg = curr;
      else
      prev->narg = curr;
      prev = curr;
    }
  }
      
  t_result->type = (i == 0 ? NAME : COMPLEX) ;
  /* note that no sym_num is assigned; this should be ok */
  return(t_result);

}  /* set_multiset_diff */

/*************
 *
 *   int lrpo_multiset(t1, t2) -- Is t1 > t2 in the lrpo multiset ordering?
 *
 *   t1 and t2 have functors with the same precedence.
 *
 *   let n(a,t) be the number of occurrences of a (as an argument) in t.
 *
 *   t1 >(multiset) t2 iff for each arg a2 of t2 with n(a2,t2) > n(a2,t1),
 *   there is an arg a1 of t1 such that  n(a1,t1) > n(a1,t2), and a1>a2.
 *
 *************/

static int lrpo_multiset(struct term *t1,
                   struct term *t2)
{
  struct term *s1, *s2;
  struct rel *r1, *r2;
  int ok;

  s1 = set_multiset_diff(t1, t2);  /* builds and returns a set */
  s2 = set_multiset_diff(t2, t1);  /* builds and returns a set */

  /*
   * return (s2 not empty and foreach arg a2 of s2
   *    there is an arg a1 of s1 such that lrpo(a1, a2)).
   */

  if (s2->farg == NULL)
    ok = 0;
  else {
    for (r2 = s2->farg, ok = 1; r2 && ok; r2 = r2->narg) {
      for (r1 = s1->farg, ok = 0; r1 && !ok ; r1 = r1->narg)
      ok = lrpo(r1->argval, r2->argval);
    }
  }

  zap_term(s1);
  zap_term(s2);

  return(ok);

}  /* lrpo_multiset */

/*************
 *
 *   int lrpo(t1, t2) - Is t1 > t2 in the lexicographic recursive
 *                      path ordering?
 *
 *************/

int lrpo(struct term *t1,
       struct term *t2)
{
  int p;
  struct rel *r;

  if (t1->type == VARIABLE)
    /* varaiable never greater than anything */
    return(0);
  else if (t2->type == VARIABLE)
    /* t1 > variable iff t1 properly contains that variable */
    return(occurs_in(t2, t1));
  else if (t1->sym_num == t2->sym_num &&
         lrpo_status(t1->sym_num) == LRPO_LR_STATUS)
    return(lrpo_lex(t1, t2));
  else {
    p = sym_precedence(t1->sym_num, t2->sym_num);
    if (p == SAME_AS)
      return(lrpo_multiset(t1,t2));
    else if (p == GREATER_THAN) {
      /* return (t1 > each arg of t2) */
      for (r = t2->farg; r && lrpo(t1, r->argval); r = r->narg)
      /* empty body */ ;
      return(r == NULL);
    }
    else {  /* LESS_THEN or NOT_COMPARABLE */
      /* return (there is an arg of t1 s.t. arg == t2 or arg > t2) */
      for (r = t1->farg; r; r = r->narg) {
      if (term_ident(r->argval, t2) || lrpo(r->argval, t2))
        return(1);
      }
      return(0);
    }
  }
}  /* lrpo */

/*************
 *
 *   int lrpo_greater(t1, t2) - Is t1 > t2 in the lexicographic
 *                              recursive path ordering?
 *
 *    Time this routine.
 *
 *************/

int lrpo_greater(struct term *t1,
             struct term *t2)
{
  int rc;

#if 0
  CLOCK_START(LRPO_TIME);
  rc = lrpo(t1,t2);
  CLOCK_STOP(LRPO_TIME);
#else
  rc = lrpo(t1,t2);
#endif
  return(rc);

}  /* lrpo_greater */

/*************
 *
 *    order_equalities_lrpo(c)
 *
 *    For each equality literal (pos or neg), flip args if the right
 *    side is heavier.  After possible flip, if the left side is
 *    heavier, set the ORIENTED_EQ_BIT in the atom.
 *    If the atom is flipped, set SCRATCH_BIT.
 *
 *************/

void order_equalities_lrpo(struct clause *c)
{
  struct rel *r1, *r2;
  struct term *alpha, *beta;
  struct literal *l;

  for (l = c->first_lit; l; l = l->next_lit) {
    if (eq_lit(l)) {
      r1 = l->atom->farg;
      r2 = r1->narg;
      alpha = r1->argval;
      beta  = r2->argval;
      if (lrpo_greater(alpha, beta))
      SET_BIT(l->atom->bits, ORIENTED_EQ_BIT);
      else if (lrpo_greater(beta, alpha)) {
      r1->argval = beta;
      r2->argval = alpha;
      SET_BIT(l->atom->bits, SCRATCH_BIT);
      SET_BIT(l->atom->bits, ORIENTED_EQ_BIT);
      }
    }
  }
}  /* order_equalities_lrpo */


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