JPEGView/Independent JPEG Group/jmemdos.c

/*
 * jmemdos.c
 *
 * 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 file provides an MS-DOS-compatible implementation of the system-
 * dependent portion of the JPEG memory manager.  Temporary data can be
 * stored in extended or expanded memory as well as in regular DOS files.
 *
 * If you use this file, you must be sure that NEED_FAR_POINTERS is defined
 * if you compile in a small-data memory model; it should NOT be defined if
 * you use a large-data memory model.  This file is not recommended if you
 * are using a flat-memory-space 386 environment such as DJGCC or Watcom C.
 * Also, this code will NOT work if struct fields are aligned on greater than
 * 2-byte boundaries.
 *
 * Based on code contributed by Ge' Weijers.
 */

/*
 * If you have both extended and expanded memory, you may want to change the
 * order in which they are tried in jopen_backing_store.  On a 286 machine
 * expanded memory is usually faster, since extended memory access involves
 * an expensive protected-mode-and-back switch.  On 386 and better, extended
 * memory is usually faster.  As distributed, the code tries extended memory
 * first (what? not everyone has a 386? :-).
 *
 * You can disable use of extended/expanded memory entirely by altering these
 * definitions or overriding them from the Makefile (eg, -DEMS_SUPPORTED=0).
 */

#ifndef XMS_SUPPORTED
#define XMS_SUPPORTED  1
#endif
#ifndef EMS_SUPPORTED
#define EMS_SUPPORTED  1
#endif


#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jmemsys.h"		/* import the system-dependent declarations */

#ifndef HAVE_STDLIB_H		/* <stdlib.h> should declare these */
extern void * malloc JPP((size_t size));
extern void free JPP((void *ptr));
extern char * getenv JPP((const char * name));
#endif

#ifdef NEED_FAR_POINTERS

#ifdef __TURBOC__
/* These definitions work for Borland C (Turbo C) */
#include <alloc.h>		/* need farmalloc(), farfree() */
#define far_malloc(x)	farmalloc(x)
#define far_free(x)	farfree(x)
#else
/* These definitions work for Microsoft C and compatible compilers */
#include <malloc.h>		/* need _fmalloc(), _ffree() */
#define far_malloc(x)	_fmalloc(x)
#define far_free(x)	_ffree(x)
#endif

#else /* not NEED_FAR_POINTERS */

#define far_malloc(x)	malloc(x)
#define far_free(x)	free(x)

#endif /* NEED_FAR_POINTERS */

#ifdef DONT_USE_B_MODE		/* define mode parameters for fopen() */
#define READ_BINARY	"r"
#else
#define READ_BINARY	"rb"
#endif

#if MAX_ALLOC_CHUNK >= 65535L	/* make sure jconfig.h got this right */
  MAX_ALLOC_CHUNK should be less than 64K. /* deliberate syntax error */
#endif


/*
 * Declarations for assembly-language support routines (see jmemdosa.asm).
 *
 * The functions are declared "far" as are all pointer arguments;
 * this ensures the assembly source code will work regardless of the
 * compiler memory model.  We assume "short" is 16 bits, "long" is 32.
 */

typedef void far * XMSDRIVER;	/* actually a pointer to code */
typedef struct {		/* registers for calling XMS driver */
	unsigned short ax, dx, bx;
	void far * ds_si;
      } XMScontext;
typedef struct {		/* registers for calling EMS driver */
	unsigned short ax, dx, bx;
	void far * ds_si;
      } EMScontext;

EXTERN short far jdos_open JPP((short far * handle, char far * filename));
EXTERN short far jdos_close JPP((short handle));
EXTERN short far jdos_seek JPP((short handle, long offset));
EXTERN short far jdos_read JPP((short handle, void far * buffer,
				unsigned short count));
EXTERN short far jdos_write JPP((short handle, void far * buffer,
				 unsigned short count));
EXTERN void far jxms_getdriver JPP((XMSDRIVER far *));
EXTERN void far jxms_calldriver JPP((XMSDRIVER, XMScontext far *));
EXTERN short far jems_available JPP((void));
EXTERN void far jems_calldriver JPP((EMScontext far *));


/*
 * Selection of a file name for a temporary file.
 * This is highly system-dependent, and you may want to customize it.
 */

static int next_file_