/* File:      cut_xsb.h
** Author(s): Kostis Sagonas
** Contact:   xsb-contact@cs.sunysb.edu
** 
** Copyright (C) The Research Foundation of SUNY, 1986, 1993-1998
** 
** 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: cut_xsb.h,v 1.13 2002/10/04 21:38:39 lfcastro Exp $
** 
*/

#ifndef __CUT_XSB_H__
#define __CUT_XSB_H__

/*----------------------------------------------------------------------*/
/* This file contains code for cuts.  It was written in December 1997	*/
/* by Kostis Sagonas based on the code written by Terry Swift and Rui	*/
/* Marques for unwinding the trail.  The input of Bart Demoen is also	*/
/* acknowledged.							*/
/* 									*/
/* The main problem is to find which part of the trail to clean up.	*/
/* Cleaning the trail means deleting trail frames for bindings that are	*/
/* no longer conditional, i.e. unbinding these variables.  In general,	*/
/* one needs to tidy/unwind the part of the trail that lies between the	*/
/* current choice point (breg) and the choice point that is immediately	*/
/* _after_ the choice point that we are really cut back to (cut_breg).	*/
/* Of course, if we are cutting to the current choice point which often	*/
/* happens, or if there is nothing in between, there is no need to	*/
/* check whether there is trail to unwind.				*/
/* This is the general scheme and the code that pretty much implements  */
/* this, is as follows:                                         	*/
/*									*/
/*	#define cut_code(OP1)						*/
/*	    XSB_Deref(OP1);						*/
/*	    cut_breg = (CPtr)(tcpstack.high - oint_val(OP1));		*/
/*	    cut_restore_trail_condition_registers(cut_breg);		*/
/*	    if (breg != cut_breg) {					*/
/*		while (cp_prevbreg(breg) != cut_breg)			*/
/*		    breg = cp_prevbreg(breg);				*/
/*		unwind_trail(breg,xtemp1,xtemp2);			*/
/*		breg = cut_breg;					*/
/*	    } goto contcase;						*/
/*									*/
/*----------------------------------------------------------------------*/

#define CHECK_TABLE_CUT(instruc)       \
  if (check_table_cut)                 \
    switch (instruc) {                 \
    case check_complete:               \
    case resume_compl_suspension:      \
    case answer_return:                \
    case tabletrust:                   \
    case tableretry:                   \
      if (!is_completed(tcp_subgoal_ptr(breg))) {\
          Psc psc = TIF_PSC(subg_tif_ptr(tcp_subgoal_ptr(breg)));\
          Psc call_psc = *(*((Psc **)ereg-1)-1);  \
          xsb_abort("Illegal cut over a tabled predicate: %s/%d, from within a call to %s/%d\n", \
		    get_name(psc), get_arity(psc),          \
		    get_name(call_psc), get_arity(call_psc));          \
      }                                \
      break;                           \
    default:                           \
      break;                           \
    }


#define cut_code(OP1)	                                        \
   { CPtr cut_breg;					        \
     byte inst_cut_over;                                        \
     CPtr xtemp1, xtemp2;                                       \
								\
     XSB_Deref(OP1);						\
     cut_breg = (CPtr)(tcpstack.high - oint_val(OP1));		\
     cut_restore_trail_condition_registers(cut_breg);		\
     if (breg != cut_breg) { /* not cutting back to the current CP */\
/*      xsb_dbgmsg("Tidying trail (cutbreg = %p, breg = %p)", cut_breg,breg); */\
	while (cp_prevbreg(breg) != cut_breg) {			\
           inst_cut_over = *cp_pcreg(breg);                     \
           CHECK_TABLE_CUT(inst_cut_over) ;                     \
	   breg = cp_prevbreg(breg);				\
	}							\
        inst_cut_over = *cp_pcreg(breg);                        \
        CHECK_TABLE_CUT(inst_cut_over) ;                        \
        unwind_trail(breg,xtemp1,xtemp2);			\
	breg = cut_breg;					\
     }								\
     check_table_cut = TRUE;                                    \
     XSB_Next_Instr();		       			        \
   }

/*----------------------------------------------------------------------*/
/* Takes a pointer to the choice point frame we are cutting back to.	*/
/*----------------------------------------------------------------------*/

#define cut_restore_trail_condition_registers(CUTB) \
    if ((CPtr)  *CUTB >= (CPtr) pdl.low || \
		*CUTB == (Cell) &answer_return_inst || \
                *CUTB == (Cell) &resume_compl_suspension_inst ||\
                *CUTB == (Cell) &resume_compl_suspension_inst2) { \
	ebreg = cp_ebreg(CUTB); \
	hbreg = cp_hreg(CUTB); \
    }

/*----------------------------------------------------------------------*/
/* Deletes all trail frames that are no longer conditional.		*/
/* Most probably, it does *NOT* work for cuts over tables!!		*/
/*----------------------------------------------------------------------*/

#define trail_parent(t)         ((CPtr *)*(t))
#define trail_value(t)          ((CPtr *)*((t)-1))
#define trail_variable(t)       ((CPtr *)*((t)-2))
#define good_trail_register(t)	(conditional(((CPtr) *((t)-2))))

#define unwind_trail(tbreg, t1, t2) {	\
    while (trreg > trfreg &&						\
           !good_trail_register(trreg) &&				\
	   trreg > cp_trreg(tbreg))					\
      trreg = trail_parent(trreg);					\
    (t2) = (CPtr) trail_parent((t1) = (CPtr)trreg);			\
    while ((t2) > (CPtr) cp_trreg(tbreg) && (t2) > (CPtr) trfreg) {	\
      if (!good_trail_register(t2)) {					\
	(t2) = (CPtr) trail_parent(t2);					\
	*(t1) = (Cell) (t2);						\
      } else {								\
	(t1) = (t2);							\
	(t2) = (CPtr) trail_parent(t2);					\
      }									\
    }									\
  }


#endif /* __CUT_XSB_H__ */