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$Header: d:/cvsroot/tads/TADS2/OBJ.H,v 1.3 1999/07/11 00:46:30 MJRoberts Exp $

 *   Copyright (c) 1991, 2002 Michael J. Roberts.  All Rights Reserved.
 *   Please see the accompanying license file, LICENSE.TXT, for information
 *   on using and copying this software.  
  obj.h - object definitions
  Defines interface for object handling routines
  An object is divided into two parts:  a "static" part and a "dynamic"
  part.  The static part contains all of the properties originally
  defined in the object; none of these properties can be deleted, but
  they can have a flag set to indicate that they are to be ignored,
  which effectively deletes them.  The dynamic part changes at run-time,
  with properties deleted and changed as requested.
  The static part is kept around at all times to allow objects to revert
  back to their original state with very little work.  For TADS games,
  this allows objects to be restored to their pre-play state after game
  play, without requiring a separate snapshot of the objects.  In
  addition, it allows object state to be saved in a very compact format,
  because only the object header and dynamic portion need to be written;
  the static portion, which may contain a large amount of code, need not
  be saved when saving object state.
  08/11/91 MJRoberts     - creation


#include "prp.h"
#include "dat.h"
#include "mcm.h"
#include "err.h"

#ifdef __cplusplus
extern "C" {

/* object number */
typedef ushort objnum;

 *   For non-class objects, we'll leave some space free in the object so
 *   that a few properties can be added without having to resize the
 *   object.  Class objects will probably never have anything added, so
 *   there's no need for extra space.  
#define OBJEXTRA 64

/* object structure */
struct objdef
    ushort   objws;                      /o workspace object was defined in o/
    ushort   objflg;                                        /o object flags o/
    ushort   objnsc;                              /o number of superclasses o/
    ushort   objnprop;            /o number of properties defined in object o/
    ushort   objfree;          /o offset of next free byte in property area o/
    ushort   objrst;        /o reset point - offset of end of 'static' part o/
    ushort   objstat;                      /o number of 'static' properties o/
    objnum   objsc[1];                                      /o superclasses o/
typedef struct objdef objdef;
#   define   OBJFCLS   0x01                            /* object is a class */

   The object structure is actually laid out portably, using unaligned
   2-byte arrays, stored least significant byte first, for each ushort
   (including the objnum array for the superclasses).  The actual
   entries are at these offsets on all machines: 
      objws      0
      objflg     2
      objnsc     4
      objnprop   6
      objfree    8
      objrst     10
      objstat    12
      objsc[0]   14
      objsc[1]   16
   If the OBJFINDEX flag is set, the object has a property index.
   The index occurs after the last superclass (so it's where the
   property data would go if there were no index), and the property
   data follows.  Each index entry consists of a pair of two-byte
   entries:  the first is the property number, and the second is
   its offset within the object.  For performance reasons, an index
   is only built on a class object -- whenever a property is changed
   within an object, the entire index must be rebuilt, because the
   locations of many properties within the object can be changed by
   a single property change in the object.  The index is ordered by
   property number, so it can be searched using a binary search.
   Furthermore, "ignored" properties are excluded from the index;
   only the active instance of a particular property is stored.
   The index must be maintained by all routines that can change
   property information:  setp, delp, revert, etc.
   Preceding the index table is a two-byte entry that gives the
   offset of the properties.  Since the properties immediately
   follow the index, this can be used to deduce how large a space
   is available for the index itself.
typedef uchar objdef;
#define OBJDEFSIZ 14   /* "sizeof(objdef)" - size of object header w/o sc's */

/* object flags */
#define OBJFCLASS  1                                   /* object is a class */
#define OBJFINDEX  2                         /* object has a property index */
#define OBJFMOD    4      /* object has been modified by a newer definition */

/* undo context */
struct objucxdef
    mcmcxdef *objucxmem;                           /* cache manager context */
    errcxdef *objucxerr;                                   /* error context */
    ushort    objucxsiz;                         /* size of the undo buffer */
    ushort    objucxhead;                  /* head (position of next write) */
    ushort    objucxtail;               /* tail (position of oldest record) */
    ushort    objucxprv;                           /* previous head pointer */
    ushort    objucxtop;                      /* highest head value written */
    void    (*objucxcun)(void *ctx, uchar *data);
                                              /* apply a client undo record */
    ushort  (*objucxcsz)(void *ctx, uchar *data);
                                        /* get size of a client undo record */
    void     *objucxccx;                             /* client undo context */
    uchar     objucxbuf[1];                                  /* undo buffer */
typedef struct objucxdef objucxdef;

 *   Undo records are kept in a circular buffer allocated as part of an
 *   undo context.  Offsets within the buffer are kept for the head, tail,
 *   and previous head records.  The head always points to the byte at
 *   which the next undo record will be written.  The previous head points
 *   to the most recently written undo record; it contains a back link to
 *   the undo record before that, and so forth back through the entire
 *   chain.  (These reverse links are necessary because undo records vary
 *   in size depending on the data contained within.)  The tail points to
 *   the oldest undo record that's still in the buffer.  Conceptually, the
 *   head is always "above" the tail in the buffer; since the buffer is
 *   circular, the tail may have a higher address, but this just means
 *   that the buffer wraps around at the top.  When the head bumps into
 *   the tail (i.e., the head address is physically below or equal to the
 *   tail address, and the head is then advanced so that its address
 *   becomes higher than the tail's), the tail is advanced by discarding
 *   as many of the least recent undo records as necessary to make room
 *   for the new head position.  When the head and the previous head point
 *   to the same place, we have no undo records in the buffer.  
 *   The first byte of an undo record specifies what action is to be
 *   undone.  If a property was added, it is undone merely by deleting the
 *   property.  If a property was changed, it is undone by setting the
 *   property back to its old value.  An additional special flag indicates
 *   a "savepoint."  Normally, all changes back to a savepoint will be
 *   undone.  
#define OBJUADD    1             /* a property was added (undo by deleting) */
#define OBJUCHG    2   /* a property was changed (change back to old value) */
#define OBJUSAV    3          /* savepoint marker (no property information) */
#define OBJUOVR    4     /* override original property (set orig to IGNORE) */
#define OBJUCLI    5                /* client undo record (any client data) */

 *   After the control byte (OBJUxxx), the object number, property
 *   number, datatype, and data value will follow; some or all of these
 *   may be omitted, depending on the control byte. 

/* get object flags */
#define objflg(o) ((ushort)osrp2(((char *)(o)) + 2))

/* get object flags */
#define objsflg(o, val) oswp2(((char *)(o)) + 2, val)

/* given an object pointer, get a pointer to the first prpdef */
/* prpdef *objprp(objdef *objptr); */
#define objprp(o) ((prpdef *)(objsc(o) + 2*objnsc(o)))

/* given an object pointer, get number of properties in the prpdef */
/* int objnprop(objdef *objptr); */
#define objnprop(o) ((ushort)osrp2(((char *)(o)) + 6))

/* set number of properties */
/* void objsnp(objdef *objptr, int newnum); */
#define objsnp(o,n) oswp2(((char *)(o)) + 6, n)

/* given an object pointer, get offset of free space */
/* int objfree(objdef *objptr); */
#define objfree(o) ((ushort)osrp2(((char *)(o)) + 8))

/* set free space pointer */
/* void objsfree(objdef *objptr, int newfree); */
#define objsfree(o,n) oswp2(((char *)(o)) + 8, n)

/* get number of static properties */
/* ushort objstat(objdef *objptr); */
#define objstat(o) ((ushort)osrp2(((char *)(o)) + 10))

/* set number of static properties */
/* void objsetst(objdef *objptr, int newstat); */
#define objsetst(o,n) oswp2(((char *)(o)) + 10, n)

/* get reset size (size of static properties) */
/* ushort objrst(objdef *objptr); */
#define objrst(o) ((ushort)osrp2(((char *)(o)) + 12))

/* set reset size */
/* void objsetrst(objdef *objptr, uint newrst); */
#define objsetrst(o,n) oswp2(((char *)(o)) + 12, n)
/* given an object pointer, get first superclass pointer */
/* uchar *objsc(objdef *objptr); */
#define objsc(o) (((uchar *)(o)) + OBJDEFSIZ)

/* given an object pointer, get number of superclasses */
/* int objnsc(objdef *objptr); */
#define objnsc(o) ((ushort)osrp2(((char *)(o)) + 4))

/* set number of superclasses */
/* void objsnsc(objdef *objptr, int num); */
#define objsnsc(o,n) oswp2(((char *)(o)) + 4, n)

/* given a prpdef, get the next prpdef */
/* prpdef *objpnxt(prpdef *p); */
#define objpnxt(p) \
 ((prpdef *)(((uchar *)(p)) + PRPHDRSIZ + prpsize(p)))

/* get pointer to free prpdef */
/* prpdef *objpfre(objdef *objptr); */
#define objpfre(o) ((prpdef *)(((uchar *)(o)) + objfree(o)))

/* given a prpdef and an object pointer, compute the prpdef offset */
/* uint objpofs(objdef *objptr, prpdef *propptr); */
#define objpofs(o,p) ((uint)((p) ? (((uchar *)(p)) - ((uchar *)(o))) : 0))

/* given an object pointer and a property offset, get prpdef pointer */
/* prpdef *objofsp(objdef *objptr, uint propofs); */
#define objofsp(o,ofs) ((prpdef *)((ofs) ? (((uchar *)(o)) + (ofs)) : 0))

 *   Get the first superclass of an object.  If it doesn't have any
 *   superclasses, return invalid.
objnum objget1sc(mcmcxdef *ctx, objnum objn);

 *   Get an object's property WITHOUT INHERITANCE.  If the object has the
 *   indicated property set, the byte OFFSET of the prpdef within the
 *   object is returned.  The offset will remain valid until any type of
 *   operation that sets a property in the object (such as objdelp,
 *   objsetp, or an undo operation).  An offset of zero means that the
 *   property was not set in the object.
uint objgetp(mcmcxdef *ctx, objnum objn, prpnum prop,
             dattyp *typptr);

 *   Get the *ending* offset of the given property's value, without any
 *   inheritance.  Returns the byte offset one past the end of the
 *   property's data.  
uint objgetp_end(mcmcxdef *ctx, objnum objn, prpnum prop);

 *   Get a property of an object, either from the object or from a
 *   superclass (inherited).  If the inh flag is TRUE, we do not look
 *   at all in the object itself, but restrict our search to inherited
 *   properties only.  We return the byte OFFSET of the prpdef within
 *   the object in which the prpdef is found; the superclass object
 *   itself is NOT locked upon return, but we will NOT unlock the
 *   object passed in.  If the offset is zero, the property was not
 *   found.  The offset returned is valid until any operation that
 *   sets a property in the object (such as objdelp, objsetp, or an
 *   undo operation).
uint objgetap(mcmcxdef *ctx, noreg objnum objn, prpnum prop,
              objnum *orn, int inh);

 *   expand an object by a requested amount, returning a pointer to the
 *   object's new location if it must be moved.  The object will be
 *   unlocked and relocked by this call.  On return, the actual amount
 *   of space ADDED to the object will be returned.
objdef *objexp(mcmcxdef *ctx, objnum obj, ushort *siz);

 *   Set an object's property, deleting the original value of the
 *   property if it existed.  If an undo context is provided, write an
 *   undo record for the change; if the undo context pointer is null, no
 *   undo information is retained. 
void objsetp(mcmcxdef *ctx, objnum obj, prpnum prop,
             dattyp typ, void *val, objucxdef *undoctx);

 *   Delete a property.  If mark_only is true, we'll only mark the
 *   property as deleted without actually reclaiming its space; this is
 *   necessary when removing a code property (type DAT_CODE) any time
 *   other code properties may follow, because p-code is not entirely
 *   self-relative and thus can't always be relocated within an object. 
void objdelp(mcmcxdef *mctx, objnum objn, prpnum prop, int mark_only);

 *   Set up for emitting code into an object.  Writes a property header
 *   of type 'code', and returns the offset of the next free byte in the
 *   object.  Call objendemt when done.  The datatype argument is
 *   provided so that list generation can be done through the same
 *   mechanism, since parser lists must be converted to run-time
 *   lists via the code generator.
uint objemt(mcmcxdef *ctx, objnum objn, prpnum prop, dattyp typ);

/* done emitting code into property, finish setting object info */
void objendemt(mcmcxdef *ctx, objnum objn, prpnum prop, uint endofs);

 *   Determine if undo records should be kept.  Undo records should be
 *   kept only if a savepoint is present in the undo log.  If no savepoint
 *   is present, adding undo records would be useless, since it will not
 *   be possible to apply the undo information. 
int objuok(objucxdef *undoctx);

 *   Reserve space in an undo buffer, deleting old records as needed.
 *   Returns a pointer to the reserved space. 
uchar *objures(objucxdef *undoctx, uchar cmd, ushort siz);

/* advance the tail pointer in an undo buffer over the record it points to */
void objutadv(objucxdef *undoctx);

/* apply one undo record, and remove it from undo list */
void obj1undo(mcmcxdef *mctx, objucxdef *undoctx);

 *   Undo back to the most recent savepoint.  If there is no savepoint in
 *   the undo list, NOTHING will be undone.  This prevents reaching an
 *   inconsistent state in which some, but not all, of the operations
 *   between two savepoints are undone: either all operations between two
 *   savepoints will be undone, or none will. 
void objundo(mcmcxdef *mctx, objucxdef *undoctx);

/* set an undo savepoint */
void objusav(objucxdef *undoctx);

/* initialize undo context */
objucxdef *objuini(mcmcxdef *memctx, ushort undosiz,
                   void (*undocb)(void *ctx, uchar *data),
                   ushort (*sizecb)(void *ctx, uchar *data),
                   void *callctx);

/* discard all undo context (for times such as restarting) */
void objulose(objucxdef *undoctx);

 *   Allocate and initialize a new object.  The caller specifies the
 *   number of superclasses to be allocated, and the amount of space (in
 *   bytes) for the object's property data.  The caller must fill in the
 *   superclass array.  Upon return, the object is allocated and locked,
 *   and is initialized with no properties.  A pointer to the object's
 *   memory is returned, and *objnptr receives the object number.
objdef *objnew(mcmcxdef *mctx, int sccnt, ushort propspace,
               objnum *objnptr, int classflg);
/* initialize an already allocated object */
void objini(mcmcxdef *mctx, int sccnt, objnum objn, int classflg);

 *   Add space for additional superclasses to an object.  The object can
 *   already have some properties set (if it doesn't, it can just be
 *   reinitialized).
void objaddsc(mcmcxdef *mctx, int sccnt, objnum objn);

 *   Delete an object's properties and superclasses.  The 'mindel'
 *   parameter specifies the minimum property number to be deleted.
 *   Properties below this are considered "system" properties that are not
 *   to be deleted.  This could be used by a development environment to
 *   store the source for an object as a special system property in the
 *   object; when the object is recompiled, all of the object's properties
 *   and superclasses must be deleted except the source property, which is
 *   retained even after recompilation. 
void objclr(mcmcxdef *mctx, objnum objn, prpnum mindel);

/* Build or rebuild an object's property index */
void objindx(mcmcxdef *mctx, objnum objn);

/* set up just-compiled object: mark static part and original properties */
void objcomp(mcmcxdef *mctx, objnum objn, int for_debug);

/* revert an object to original post-compilation state */
void objrevert(void *mctx, mcmon objn);

/* reset 'ignore' flags for a newly reconstructed object */
void objsetign(mcmcxdef *mctx, objnum objn);

#ifdef __cplusplus

#endif /* OBJ_INCLUDED */

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