deref.h

/* File:      deref.h
** Author(s): Jiyang Xu, Terrance Swift, Kostis Sagonas
** Contact:   xsb-contact@cs.sunysb.edu
** 
** Copyright (C) The Research Foundation of SUNY, 1986, 1993-1998
** Copyright (C) ECRC, Germany, 1990
** 
** XSB 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.
** 
** XSB 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 XSB; if not, write to the Free Software Foundation,
** Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
**
** $Id: deref.h,v 1.8 2005/10/21 17:47:52 tswift Exp $
** 
*/

#ifndef __DEREF_H__
#define __DEREF_H__

/* TLS: Bao changed these derefs to handle attributed variables, since
 *  a reference chain can, in principle, have a chain of var pointers
 *  followed by a chain of attv pointers, ending in a free variable.
 *  Actually, the code here is somewhat more general, and allows more
 *  intermixture of attv and var pointers.  So I may be wrong or the
 *  code may be a little more general than it needs to be.
 * 
 *  XSB_Deref(op) is the same as XSB_CptrDeref(op) except that
 *  XSB_CptrDeref(op) performs an explicit cast of op to a CPtr.  */

#define XSB_Deref(op) XSB_Deref2(op,break)

/* XSB_Deref2 is changed to consider attributed variables */
#define XSB_Deref2(op, stat) {                          \
  while (isref(op)) {                                   \
    if (op == follow(op))                               \
      stat;                                             \
    op = follow(op);                                    \
  }                                                     \
  while (isattv(op)) {                                  \
    if (cell((CPtr) dec_addr(op)) == dec_addr(op))      \
      break; /* end of an attv */                       \
    else {                                              \
      op = cell((CPtr) dec_addr(op));                   \
      while (isref(op)) {                               \
        if (op == follow(op))                           \
          stat;                                         \
        op = follow(op);                                \
      }                                                 \
    }                                                   \
  }                                                     \
}

#define XSB_CptrDeref(op) {                             \
  while (isref(op)) {                                   \
    if (op == (CPtr) cell(op)) break;                   \
    op = (CPtr) cell(op);                               \
  }                                                     \
  while (isattv(op)) {                                  \
    if (cell((CPtr) dec_addr(op)) == dec_addr(op))      \
      break;                                            \
    else {                                              \
      op = (CPtr) cell((CPtr) dec_addr(op));            \
      while (isref(op)) {                               \
        if (op == (CPtr) cell(op)) break;               \
        op = (CPtr) cell(op);                           \
      }                                                 \
    }                                                   \
  }                                                     \
}

#define printderef(op) while (isref(op) && op > 0) { \
                         if (op==follow(op)) \
                            break; \
                         op=follow(op); }
#endif /* __DEREF_H__ */

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