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jmemsys.h
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jmemsys.h
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/*
* jmemsys.h
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1992-1997, Thomas G. Lane.
* It was modified by The libjpeg-turbo Project to include only code and
* information relevant to libjpeg-turbo.
* For conditions of distribution and use, see the accompanying README.ijg
* 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.
*/
/*
* 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.
*/
EXTERN(void *) jpeg_get_small (j_common_ptr cinfo, size_t sizeofobject);
EXTERN(void) jpeg_free_small (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).
* 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 *) jpeg_get_large (j_common_ptr cinfo, size_t sizeofobject);
EXTERN(void) jpeg_free_large (j_common_ptr cinfo, void *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 was needed
* to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
* On machines with 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(size_t) jpeg_mem_available (j_common_ptr cinfo, size_t min_bytes_needed,
size_t max_bytes_needed,
size_t 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 */
#ifdef USE_MAC_MEMMGR /* Mac-specific junk */
#include <Files.h>
#endif /* USE_MAC_MEMMGR */
typedef struct backing_store_struct *backing_store_ptr;
typedef struct backing_store_struct {
/* Methods for reading/writing/closing this backing-store object */
void (*read_backing_store) (j_common_ptr cinfo, backing_store_ptr info,
void *buffer_address, long file_offset,
long byte_count);
void (*write_backing_store) (j_common_ptr cinfo, backing_store_ptr info,
void *buffer_address, long file_offset,
long byte_count);
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
#ifdef USE_MAC_MEMMGR
/* For the Mac manager (jmemmac.c), we need: */
short temp_file; /* file reference number to temp file */
FSSpec tempSpec; /* the FSSpec for the temp file */
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
#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 (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 (j_common_ptr cinfo);
EXTERN(void) jpeg_mem_term (j_common_ptr cinfo);