File: ostack.h

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/* Copyright (C) 2001-2006 Artifex Software, Inc.
   All Rights Reserved.
  
   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied, modified
   or distributed except as expressly authorized under the terms of that
   license.  Refer to licensing information at http://www.artifex.com/
   or contact Artifex Software, Inc.,  7 Mt. Lassen Drive - Suite A-134,
   San Rafael, CA  94903, U.S.A., +1(415)492-9861, for further information.
*/

/* $Id: ostack.h 9043 2008-08-28 22:48:19Z giles $ */
/* Definitions for Ghostscript operand stack */

#ifndef ostack_INCLUDED
#  define ostack_INCLUDED

#include "iostack.h"
#include "icstate.h"		/* for access to op_stack */

/* Define the operand stack pointers for operators. */
#define iop_stack (i_ctx_p->op_stack)
#define o_stack (iop_stack.stack)

#define osbot (o_stack.bot)
#define osp (o_stack.p)
#define ostop (o_stack.top)

/* Macro to ensure enough room on the operand stack */
#define check_ostack(n)\
  if ( ostop - osp < (n) )\
    { o_stack.requested = (n); return_error(e_stackoverflow); }

/* Operand stack manipulation. */

/* Note that push sets osp to (the new value of) op. */
#define push(n)\
  BEGIN\
    if ( (op += (n)) > ostop )\
      { o_stack.requested = (n); return_error(e_stackoverflow); }\
    else osp = op;\
  END

/*
 * Note that the pop macro only decrements osp, not op.  For this reason,
 *
 *      >>>     pop should only be used just before returning,  <<<
 *      >>>     or else op must be decremented explicitly.      <<<
 */
#define pop(n) (osp -= (n))

/*
 * Note that the interpreter does not check for operand stack underflow
 * before calling the operator procedure.  There are "guard" entries
 * with invalid types and attributes just below the bottom of the
 * operand stack: if the operator returns with a typecheck error,
 * the interpreter checks for underflow at that time.
 * Operators that don't typecheck their arguments must check for
 * operand stack underflow explicitly; operators that take a variable
 * number of arguments must also check for stack underflow in those cases
 * where they expect more than their minimum number of arguments.
 * (This is because the interpreter can only recognize that a typecheck
 * is really a stackunderflow when the stack has fewer than the
 * operator's declared minimum number of entries.)
 */
#define check_op(nargs)\
  if ( op < osbot + ((nargs) - 1) ) return_error(e_stackunderflow)
/*
 * Similarly, in order to simplify some overflow checks, we allocate
 * a few guard entries just above the top of the o-stack.
 */

/*
 * The operand stack is implemented as a linked list of blocks:
 * operators that can push or pop an unbounded number of values, or that
 * access the entire o-stack, must take this into account.  These are:
 *      (int)copy  index  roll  clear  count  cleartomark
 *      counttomark  aload  astore  packedarray
 *      .get/.putdeviceparams .gethardwareparams
 */

#endif /* ostack_INCLUDED */