//  * jmemsys.h
//  *
//  * Copyright (C) 1992-1994, Thomas G. Lane.
//  * This file is part of the Independent JPEG Group's software.
//  * For conditions of distribution and use, see the accompanying README file.
//  *
//  * This include file defines the interface between the system-independent
//  * and system-dependent portions of the JPEG memory manager.  No other
//  * modules need include it.  (The system-independent portion is jmemmgr.c;
//  * there are several different versions of the system-dependent portion.)
//  *
//  * This file works as-is for the system-dependent memory managers supplied
//  * in the IJG distribution.  You may need to modify it if you write a
//  * custom memory manager.  If system-dependent changes are needed in
//  * this file, the best method is to #ifdef them based on a configuration
//  * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR.


// Short forms of external names for systems with brain-damaged linkers. 

#ifdef NEED_SHORT_EXTERNAL_NAMES
#define jpeg_get_small		jGetSmall
#define jpeg_free_small		jFreeSmall
#define jpeg_get_large		jGetLarge
#define jpeg_free_large		jFreeLarge
#define jpeg_mem_available	jMemAvail
#define jpeg_open_backing_store	jOpenBackStore
#define jpeg_mem_init		jMemInit
#define jpeg_mem_term		jMemTerm
#endif // NEED_SHORT_EXTERNAL_NAMES 


//  * These two functions are used to allocate and release small chunks of
//  * memory.  (Typically the total amount requested through jpeg_get_small is
//  * no more than 20K or so; this will be requested in chunks of a few K each.)
//  * Behavior should be the same as for the standard library functions malloc
//  * and free; in particular, jpeg_get_small must return NULL on failure.
//  * On most systems, these ARE malloc and free.  jpeg_free_small is passed the
//  * size of the object being freed, just in case it's needed.
//  * On an 80x86 machine using small-data memory model, these manage near heap.

EXTERN void * jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
EXTERN void jpeg_free_small JPP((j_common_ptr cinfo, void * object,
				 size_t sizeofobject));

//  * These two functions are used to allocate and release large chunks of
//  * memory (up to the total free space designated by jpeg_mem_available).
//  * The interface is the same as above, except that on an 80x86 machine,
//  * far pointers are used.  On most other machines these are identical to
//  * the jpeg_get/free_small routines; but we keep them separate anyway,
//  * in case a different allocation strategy is desirable for large chunks.

EXTERN void FAR * jpeg_get_large JPP((j_common_ptr cinfo,size_t sizeofobject));
EXTERN void jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
				 size_t sizeofobject));

//  * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
//  * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
//  * matter, but that case should never come into play).  This macro is needed
//  * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
//  * On those machines, we expect that jconfig.h will provide a proper value.
//  * On machines with 32-bit flat address spaces, any large constant may be used.
//  *
//  * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
//  * size_t and will be a multiple of sizeof(align_type).

#ifndef MAX_ALLOC_CHUNK		// may be overridden in jconfig.h 
#define MAX_ALLOC_CHUNK  1000000000L
#endif

//  * This routine computes the total space still available for allocation by
//  * jpeg_get_large.  If more space than this is needed, backing store will be
//  * used.  NOTE: any memory already allocated must not be counted.
//  *
//  * There is a minimum space requirement, corresponding to the minimum
//  * feasible buffer sizes; jmemmgr.c will request that much space even if
//  * jpeg_mem_available returns zero.  The maximum space needed, enough to hold
//  * all working storage in memory, is also passed in case it is useful.
//  * Finally, the total space already allocated is passed.  If no better
//  * method is available, cinfo->mem->max_memory_to_use - already_allocated
//  * is often a suitable calculation.
//  *
//  * It is OK for jpeg_mem_available to underestimate the space available
//  * (that'll just lead to more backing-store access than is really necessary).
//  * However, an overestimate will lead to failure.  Hence it's wise to subtract
//  * a slop factor from the true available space.  5% should be enough.
//  *
//  * On machines with lots of virtual memory, any large constant may be returned.
//  * Conversely, zero may be returned to always use the minimum amount of memory.

EXTERN LONG jpeg_mem_available JPP((j_common_ptr cinfo,
				    LONG min_bytes_needed,
				    LONG max_bytes_needed,
				    LONG already_allocated));


//  * This structure holds whatever state is needed to access a single
//  * backing-store object.  The read/write/close method pointers are called
//  * by jmemmgr.c to manipulate the backing-store object; all other fields
//  * are private to the system-dependent backing store routines.

#define TEMP_NAME_LENGTH   64	// max length of a temporary file's name 

#ifdef USE_MSDOS_MEMMGR		// DOS-specific junk 

typedef unsigned short XMSH;	// type of extended-memory handles 
typedef unsigned short EMSH;	// type of expanded-memory handles 

typedef union {
  short file_handle;		// DOS file handle if it's a temp file 
  XMSH xms_handle;		// handle if it's a chunk of XMS 
  EMSH ems_handle;		// handle if it's a chunk of EMS 
} handle_union;

#endif // USE_MSDOS_MEMMGR 

typedef struct backing_store_struct * backing_store_ptr;

typedef struct backing_store_struct {
  // Methods for reading/writing/closing this backing-store object 
  JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
				     backing_store_ptr info,
				     void FAR * buffer_address,
				     LONG file_offset, LONG byte_count));
  JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
				      backing_store_ptr info,
				      void FAR * buffer_address,
				      LONG file_offset, LONG byte_count));
  JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
				      backing_store_ptr info));

  // Private fields for system-dependent backing-store management 
#ifdef USE_MSDOS_MEMMGR
  // For the MS-DOS manager (jmemdos.c), we need: 
  handle_union handle;		// reference to backing-store storage object 
  char temp_name[TEMP_NAME_LENGTH]; // name if it's a file 
#else
  // For a typical implementation with temp files, we need: 
  FILE * temp_file;		// stdio reference to temp file 
  char temp_name[TEMP_NAME_LENGTH]; // name of temp file 
#endif
} backing_store_info;

//  * Initial opening of a backing-store object.  This must fill in the
//  * read/write/close pointers in the object.  The read/write routines
//  * may take an error exit if the specified maximum file size is exceeded.
//  * (If jpeg_mem_available always returns a large value, this routine can
//  * just take an error exit.)

EXTERN void jpeg_open_backing_store JPP((j_common_ptr cinfo,
					 backing_store_ptr info,
					 LONG total_bytes_needed));


//  * These routines take care of any system-dependent initialization and
//  * cleanup required.  jpeg_mem_init will be called before anything is
//  * allocated (and, therefore, nothing in cinfo is of use except the error
//  * manager pointer).  It should return a suitable default value for
//  * max_memory_to_use; this may subsequently be overridden by the surrounding
//  * application.  (Note that max_memory_to_use is only important if
//  * jpeg_mem_available chooses to consult it ... no one else will.)
//  * jpeg_mem_term may assume that all requested memory has been freed and that
//  * all opened backing-store objects have been closed.

EXTERN LONG jpeg_mem_init JPP((j_common_ptr cinfo));
EXTERN void jpeg_mem_term JPP((j_common_ptr cinfo));