/* Copyright (C) 1995, 1996, 1999, 2002 Aladdin Enterprises.  All rights reserved.
  
  This program is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License version 2
  as published by the Free Software Foundation.


  This software is provided AS-IS with no warranty, either express or
  implied. That is, this program 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
  General Public License for more details

  You should have received a copy of the GNU General Public License along
  with this program; if not, write to the Free Software Foundation, Inc.,
  59 Temple Place, Suite 330, Boston, MA, 02111-1307.
  
  For more information about licensing, please refer to
  http://www.ghostscript.com/licensing/. For information on
  commercial licensing, go to http://www.artifex.com/licensing/ or
  contact Artifex Software, Inc., 101 Lucas Valley Road #110,
  San Rafael, CA  94903, U.S.A., +1(415)492-9861.
*/

/* $Id: gxobj.h,v 1.6 2002/02/21 22:24:53 giles Exp $ */
/* Memory manager implementation structures for Ghostscript */

#ifndef gxobj_INCLUDED
#  define gxobj_INCLUDED

#include "gxbitmap.h"

/* ================ Objects ================ */

/*
 * Object headers have the form:
	-l- -mark/back-
	-size-
	-type/reloc-
 * l (aLone) is a single bit.  Mark/back is 1 bit shorter than a uint.  We
 * round the header size up to the next multiple of the most severe
 * alignment restriction (4 or 8 bytes).
 *
 * The mark/back field is used for the mark during the marking phase of
 * garbage collection, and for a back pointer value during the compaction
 * phase.  Since we want to be able to collect local VM independently of
 * global VM, we need two different distinguished mark values:
 *      - For local objects that have not been traced and should be freed
 *      (compacted out), we use 1...11 in the mark field (o_unmarked).
 *      - For global objects that have not been traced but should be kept,
 *      we use 1...10 in the mark field (o_untraced).
 * Note that neither of these values is a possible real relocation value.
 *
 * The back pointer's meaning depends on whether the object is
 * free (unmarked) or in use (marked):
 *      - In free objects, the back pointer is an offset from the object
 * header back to a chunk_head_t structure that contains the location
 * to which all the data in this chunk will get moved; the reloc field
 * contains the amount by which the following run of useful objects
 * will be relocated downwards.
 *      - In useful objects, the back pointer is an offset from the object
 * back to the previous free object; the reloc field is not used (it
 * overlays the type field).
 * These two cases can be distinguished when scanning a chunk linearly,
 * but when simply examining an object via a pointer, the chunk pointer
 * is also needed.
 */
#define obj_flag_bits 1
#define obj_mb_bits (arch_sizeof_int * 8 - obj_flag_bits)
#define o_unmarked (((uint)1 << obj_mb_bits) - 1)
#define o_set_unmarked(pp)\
  ((pp)->o_smark = o_unmarked)
#define o_is_unmarked(pp)\
  ((pp)->o_smark == o_unmarked)
#define o_untraced (((uint)1 << obj_mb_bits) - 2)
#define o_set_untraced(pp)\
  ((pp)->o_smark = o_untraced)
#define o_is_untraced(pp)\
  ((pp)->o_smark == o_untraced)
#define o_marked 0
#define o_mark(pp)\
  ((pp)->o_smark = o_marked)
#define obj_back_shift obj_flag_bits
#define obj_back_scale (1 << obj_back_shift)
typedef struct obj_header_data_s {
    union _f {
	struct _h {
	    unsigned alone:1;
	} h;
	struct _m {
	    unsigned _:1, smark:obj_mb_bits;
	} m;
	struct _b {
	    unsigned _:1, back:obj_mb_bits;
	} b;
    } f;
    uint size;
    union _t {
	gs_memory_type_ptr_t type;
	uint reloc;
    } t;
} obj_header_data_t;

/*
 * Define the alignment modulus for aligned objects.  We assume all
 * alignment values are powers of 2; we can avoid nested 'max'es that way.
 * The final | is because back pointer values are divided by obj_back_scale,
 * so objects must be aligned at least 0 mod obj_back_scale.
 *
 * Note: OBJECTS ARE NOT GUARANTEED to be aligned any more strictly than
 * required by the hardware, regardless of the value of obj_align_mod.
 * See gsmemraw.h for more information about this.
 */
#define obj_align_mod\
  (((arch_align_memory_mod - 1) |\
    (align_bitmap_mod - 1) |\
    (obj_back_scale - 1)) + 1)
/* The only possible values for obj_align_mod are 4, 8, or 16.... */
#if obj_align_mod == 4
#  define log2_obj_align_mod 2
#else
#if obj_align_mod == 8
#  define log2_obj_align_mod 3
#else
#if obj_align_mod == 16
#  define log2_obj_align_mod 4
#endif
#endif
#endif
#define obj_align_mask (obj_align_mod-1)
#define obj_align_round(siz)\
  (uint)(((siz) + obj_align_mask) & -obj_align_mod)
#define obj_size_round(siz)\
  obj_align_round((siz) + sizeof(obj_header_t))

/* Define the real object header type, taking alignment into account. */
struct obj_header_s {		/* must be a struct because of forward reference */
    union _d {
	obj_header_data_t o;
	byte _pad[ROUND_UP(sizeof(obj_header_data_t), obj_align_mod)];
    }
    d;
};

/* Define some reasonable abbreviations for the fields. */
#define o_alone d.o.f.h.alone
#define o_back d.o.f.b.back
#define o_smark d.o.f.m.smark
#define o_size d.o.size
#define o_type d.o.t.type
#define o_nreloc d.o.t.reloc

/*
 * The macros for getting the sizes of objects all take pointers to
 * the object header, for use when scanning storage linearly.
 */
#define pre_obj_contents_size(pp)\
  ((pp)->o_size)

#define pre_obj_rounded_size(pp)\
  obj_size_round(pre_obj_contents_size(pp))
#define pre_obj_next(pp)\
  ((obj_header_t *)((byte *)(pp) + obj_align_round(\
    pre_obj_contents_size(pp) + sizeof(obj_header_t) )))

/*
 * Define the header that free objects point back to when relocating.
 * Every chunk, including inner chunks, has one of these.
 */
typedef struct chunk_head_s {
    byte *dest;			/* destination for objects */
#if obj_align_mod > arch_sizeof_ptr
    byte *_pad[obj_align_mod / arch_sizeof_ptr - 1];
#endif
    obj_header_t free;		/* header for a free object, */
    /* in case the first real object */
    /* is in use */
} chunk_head_t;

#endif /* gxobj_INCLUDED */
