/* Copyright (C) 2001-2020 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 the license contained in the file LICENSE in this distribution.

   Refer to licensing information at http://www.artifex.com or contact
   Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
   CA 94945, U.S.A., +1(415)492-9861, for further information.
*/


/* Structure for expandable stacks of refs */
/* Requires iref.h */

#ifndef isdata_INCLUDED
#  define isdata_INCLUDED

#include "iref.h"
#include "imemory.h"

/*
 * In order to detect under- and overflow with minimum overhead, we put
 * guard elements at the top and bottom of each stack block (see idsdata.h,
 * iesdata.h, and iosdata.h for details of the individual stacks).  Note that
 * the 'current' and 'next' arrays include the guard elements.  See
 * istack.h for the details of stack blocks.
 */

/*
 * The garbage collector requires that the entire contents of every block
 * be 'clean', i.e., contain legitimate refs; we also need to ensure that
 * at GC time, pointers in unused areas of a block will not be followed
 * (since they may be dangling).  We ensure this as follows:
 *      - When allocating a new block, we set the entire body to nulls.
 *      This is necessary because the block may be freed before the next GC,
 *      and the GC must be able to scan (parse) refs even if they are free.
 *      - When adding a new block to the top of the stack, we set to nulls
 *      the unused area of the new next-to-top blocks.
 *      - At the beginning of garbage collection, we set to nulls the unused
 *      elements of the top block.
 */

/*
 * Define pointers into stacks.  Formerly, these were short (unsegmented)
 * pointers, but this distinction is no longer needed.
 */
typedef ref *s_ptr;
typedef const ref *const_s_ptr;

/*
 * Define the state of a stack, other than the data it holds.
 * Note that the total size of a stack cannot exceed max_uint,
 * because it has to be possible to copy a stack to a PostScript array.
 */

/*
 * We divide the stack structure into two parts: ref_stack_params_t, which
 * is set when the stack is created and (almost) never changed after that,
 * and ref_stack_t, which changes dynamically.
 */
typedef struct ref_stack_params_s ref_stack_params_t;
struct ref_stack_s {
    /* Following are updated dynamically. */
    s_ptr p;			/* current top element */
    /* Following are updated when adding or deleting blocks. */
    s_ptr bot;			/* bottommost valid element */
    s_ptr top;			/* topmost valid element = */
                                /* bot + data_size */
    ref current;		/* t_array for current top block */
    uint extension_size;	/* total sizes of extn. blocks */
    uint extension_used;	/* total used sizes of extn. blocks */
    /* Following are updated rarely. */
    ref max_stack;		/* t_integer, Max...Stack user param */
    uint requested;		/* amount of last failing */
                                /* push or pop request */
    uint margin;		/* # of slots to leave between limit */
                                /* and top */
    uint body_size;		/* data_size - margin */
    /* Following are set only at initialization. */
    ref_stack_params_t *params;
    gs_ref_memory_t *memory;	/* allocator for params and blocks */
};
#define public_st_ref_stack()	/* in istack.c */\
  gs_public_st_complex_only(st_ref_stack, ref_stack_t, "ref_stack_t",\
    ref_stack_clear_marks, ref_stack_enum_ptrs, ref_stack_reloc_ptrs, 0)
#define st_ref_stack_num_ptrs 2	/* current, params */

#endif /* isdata_INCLUDED */
