typedef struct {		/* XMS move specification structure */
	long length;
	XMSH src_handle;
	XMSPTR src;
	XMSH dst_handle;
	XMSPTR dst;
      } XMSspec;

#define ODD(X)	(((X) & 1L) != 0)


METHODDEF(void)
read_xms_store (j_common_ptr cinfo, backing_store_ptr info,
		void FAR * buffer_address,
		long file_offset, long byte_count)
{
  XMScontext ctx;
  XMSspec spec;
  char endbuffer[2];

  /* The XMS driver can't cope with an odd length, so handle the last byte
   * specially if byte_count is odd.  We don't expect this to be common.
   */

  spec.length = byte_count & (~ 1L);
  spec.src_handle = info->handle.xms_handle;
  spec.src.offset = file_offset;
  spec.dst_handle = 0;
  spec.dst.ptr = buffer_address;
  
  ctx.ds_si = (void far *) & spec;
  ctx.ax = 0x0b00;		/* EMB move */
  jxms_calldriver(xms_driver, (XMScontext far *) & ctx);
  if (ctx.ax != 1)
    ERREXIT(cinfo, JERR_XMS_READ);

  if (ODD(byte_count)) {
    read_xms_store(cinfo, info, (void FAR *) endbuffer,
		   file_offset + byte_count - 1L, 2L);
    ((char FAR *) buffer_address)[byte_count - 1L] = endbuffer[0];
  }
}


METHODDEF(void)
write_xms_store (j_common_ptr cinfo, backing_store_ptr info,
		 void FAR * buffer_address,
		 long file_offset, long byte_count)
{
  XMScontext ctx;
  XMSspec spec;
  char endbuffer[2];

  /* The XMS driver can't cope with an odd length, so handle the last byte
   * specially if byte_count is odd.  We don't expect this to be common.
   */

  spec.length = byte_count & (~ 1L);
  spec.src_handle = 0;
  spec.src.ptr = buffer_address;
  spec.dst_handle = info->handle.xms_handle;
  spec.dst.offset = file_offset;

  ctx.ds_si = (void far *) & spec;
  ctx.ax = 0x0b00;		/* EMB move */
  jxms_calldriver(xms_driver, (XMScontext far *) & ctx);
  if (ctx.ax != 1)
    ERREXIT(cinfo, JERR_XMS_WRITE);

  if (ODD(byte_count)) {
    read_xms_store(cinfo, info, (void FAR *) endbuffer,
		   file_offset + byte_count - 1L, 2L);
    endbuffer[0] = ((char FAR *) buffer_address)[byte_count - 1L];
    write_xms_store(cinfo, info, (void FAR *) endbuffer,
		    file_offset + byte_count - 1L, 2L);
  }
}


METHODDEF(void)
close_xms_store (j_common_ptr cinfo, backing_store_ptr info)
{
  XMScontext ctx;

  ctx.dx = info->handle.xms_handle;
  ctx.ax = 0x0a00;
  jxms_calldriver(xms_driver, (XMScontext far *) & ctx);
  TRACEMS1(cinfo, 1, JTRC_XMS_CLOSE, info->handle.xms_handle);
  /* we ignore any error return from the driver */
}


LOCAL(boolean)
open_xms_store (j_common_ptr cinfo, backing_store_ptr info,
		long total_bytes_needed)
{
  XMScontext ctx;

  /* Get address of XMS driver */
  jxms_getdriver((XMSDRIVER far *) & xms_driver);
  if (xms_driver == NULL)
    return FALSE;		/* no driver to be had */

  /* Get version number, must be >= 2.00 */
  ctx.ax = 0x0000;
  jxms_calldriver(xms_driver, (XMScontext far *) & ctx);
  if (ctx.ax < (unsigned short) 0x0200)
    return FALSE;

  /* Try to get space (expressed in kilobytes) */
  ctx.dx = (unsigned short) ((total_bytes_needed + 1023L) >> 10);
  ctx.ax = 0x0900;
  jxms_calldriver(xms_driver, (XMScontext far *) & ctx);
  if (ctx.ax != 1)
    return FALSE;

  /* Succeeded, save the handle and away we go */
  info->handle.xms_handle = ctx.dx;
  info->read_backing_store = read_xms_store;
  info->write_backing_store = write_xms_store;
  info->close_backing_store = close_xms_store;
  TRACEMS1(cinfo, 1, JTRC_XMS_OPEN, ctx.dx);
  return TRUE;			/* succeeded */
}

#endif /* XMS_SUPPORTED */


/*
 * Access methods for expanded memory.
 */

#if EMS_SUPPORTED

/* The EMS move specification structure requires word and long fields aligned
 * at odd byte boundaries.  Some compilers will align struct fields at even
 * byte boundaries.  While it's usually possible to force byte alignment,
 * that causes an overall performance penalty and may pose problems in merging
 * JPEG into a larger application.  Instead we accept some rather dirty code
 * here.  Note this code would fail if the hardware did not allow odd-byte
 * word & long accesses, but all 80x86 CPUs do.
 */

typedef void far * EMSPTR;

typedef union {			/* EMS move specification structure */
	long length;		/* It's easy to access first 4 bytes */
	char bytes[18];		/* Misaligned fields in here! */
      } EMSspec;

/* Macros for accessing misaligned fields */
#define FIELD_AT(spec,offset,type)  (*((type *) &(spec.bytes[offset])))
#define SRC_TYPE(spec)		FIELD_AT(spec,4,char)
#define SRC_HANDLE(spec)	FIELD_AT(spec,5,EMSH)
#define SRC_OFFSET(spec)	FIELD_AT(spec,7,unsigned short)
#define SRC_PAGE(spec)		FIELD_AT(spec,9,unsigned short)
#define SRC_PTR(spec)		FIELD_AT(spec,7,EMSPTR)
#define DST_TYPE(spec)		FIELD_AT(spec,11,char)
#define DST_HANDLE(spec)	FIELD_AT(spec,12,EMSH)
#define DST_OFFSET(spec)	FIELD_AT(spec,14,unsigned short)
#define DST_PAGE(spec)		FIELD_AT(spec,16,unsigned short)
#define DST_PTR(spec)		FIELD_AT(spec,14,EMSPTR)

#define EMSPAGESIZE	16384L	/* gospel, see the EMS specs */

#define HIBYTE(W)  (((W) >> 8) & 0xFF)
#define LOBYTE(W)  ((W) & 0xFF)


METHODDEF(void)
read_ems_store (j_common_ptr cinfo, backing_store_ptr info,
		void FAR * buffer_address,
		long file_offset, long byte_count)
{
  EMScontext ctx;
  EMSspec spec;

  spec.length = byte_count;
  SRC_TYPE(spec) = 1;
  SRC_HANDLE(spec) = info->handle.ems_handle;
  SRC_PAGE(spec)   = (unsigned short) (file_offset / EMSPAGESIZE);
  SRC_OFFSET(spec) = (unsigned short) (file_offset % EMSPAGESIZE);
  DST_TYPE(spec) = 0;
  DST_HANDLE(spec) = 0;
  DST_PTR(spec)    = buffer_address;
  
  ctx.ds_si = (void far *) & spec;
  ctx.ax = 0x5700;		/* move memory region */
  jems_calldriver((EMScontext far *) & ctx);
  if (HIBYTE(ctx.ax) != 0)
    ERREXIT(cinfo, JERR_EMS_READ);
}


METHODDEF(void)
write_ems_store (j_common_ptr cinfo, backing_store_ptr info,
		 void FAR * buffer_address,
		 long file_offset, long byte_count)
{
  EMScontext ctx;
  EMSspec spec;

  spec.length = byte_count;
  SRC_TYPE(spec) = 0;
  SRC_HANDLE(spec) = 0;
  SRC_PTR(spec)    = buffer_address;
  DST_TYPE(spec) = 1;
  DST_HANDLE(spec) = info->handle.ems_handle;
  DST_PAGE(spec)   = (unsigned short) (file_offset / EMSPAGESIZE);
  DST_OFFSET(spec) = (unsigned short) (file_offset % EMSPAGESIZE);
  
  ctx.ds_si = (void far *) & spec;
  ctx.ax = 0x5700;		/* move memory region */
  jems_calldriver((EMScontext far *) & ctx);
  if (HIBYTE(ctx.ax) != 0)
    ERREXIT(cinfo, JERR_EMS_WRITE);
}


METHODDEF(void)
close_ems_store (j_common_ptr cinfo, backing_store_ptr info)
{
  EMScontext ctx;

  ctx.ax = 0x4500;
  ctx.dx = info->handle.ems_handle;
  jems_calldriver((EMScontext far *) & ctx);
  TRACEMS1(cinfo, 1, JTRC_EMS_CLOSE, info->handle.ems_handle);
  /* we ignore any error return from the driver */
}


LOCAL(boolean)
open_ems_store (j_common_ptr cinfo, backing_store_ptr info,
		long total_bytes_needed)
{
  EMScontext ctx;

  /* Is EMS driver there? */
  if (! jems_available())
    return FALSE;

  /* Get status, make sure EMS is OK */
  ctx.ax = 0x4000;
  jems_calldriver((EMScontext far *) & ctx);
  if (HIBYTE(ctx.ax) != 0)
    return FALSE;

  /* Get version, must be >= 4.0 */
  ctx.ax = 0x4600;
  jems_calldriver((EMScontext far *) & ctx);
  if (HIBYTE(ctx.ax) != 0 || LOBYTE(ctx.ax) < 0x40)
    return FALSE;

  /* Try to allocate requested space */
  ctx.ax = 0x4300;
  ctx.bx = (unsigned short) ((total_bytes_needed + EMSPAGESIZE-1L) / EMSPAGESIZE);
  jems_calldriver((EMScontext far *) & ctx);
  if (HIBYTE(ctx.ax) != 0)
    return FALSE;

  /* Succeeded, save the handle and away we go */
  info->handle.ems_handle = ctx.dx;
  info->read_backing_store = read_ems_store;
  info->write_backing_store = write_ems_store;
  info->close_backing_store = close_ems_store;
  TRACEMS1(cinfo, 1, JTRC_EMS_OPEN, ctx.dx);
  return TRUE;			/* succeeded */
}

#endif /* EMS_SUPPORTED */


/*
 * Initial opening of a backing-store object.
 */

GLOBAL(void)
jpeg_open_backing_store (j_common_ptr cinfo, backing_store_ptr info,
			 long total_bytes_needed)
{
  /* Try extended memory, then expanded memory, then regular file. */
#if XMS_SUPPORTED
  if (open_xms_store(cinfo, info, total_bytes_needed))
    return;
#endif
#if EMS_SUPPORTED
  if (open_ems_store(cinfo, info, total_bytes_needed))
    return;
#endif
  if (open_file_store(cinfo, info, total_bytes_needed))
    return;
  ERREXITS(cinfo, JERR_TFILE_CREATE, "");
}


/*
 * These routines take care of any system-dependent initialization and
 * cleanup required.
 */

GLOBAL(long)
jpeg_mem_init (j_common_ptr cinfo)
{
  next_file_num = 0;		/* initialize temp file name generator */
  return DEFAULT_MAX_MEM;	/* default for max_memory_to_use */
}

GLOBAL(void)
jpeg_mem_term (j_common_ptr cinfo)
{
  /* Microsoft C, at least in v6.00A, will not successfully reclaim freed
   * blocks of size > 32Kbytes unless we give it a kick in the rear, like so:
   */
#ifdef NEED_FHEAPMIN
  _fheapmin();
#endif
}