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* jmemsys.h
* Copyright (C) 1992, 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. (The system-
* independent portion is jmemmgr.c; there are several different versions
* of the system-dependent portion, and of this file for that matter.)
* This is a "generic" skeleton that may need to be modified for particular
* systems. It should be usable as-is on the majority of non-MSDOS machines.
* These two functions are used to allocate and release small chunks of
* memory (typically the total amount requested through jget_small is
* no more than 20Kb or so). Behavior should be the same as for the
* standard library functions malloc and free; in particular, jget_small
* returns NULL on failure. On most systems, these ARE malloc and free.
* On an 80x86 machine using small-data memory model, these manage near heap.
EXTERN void * jget_small PP((size_t sizeofobject));
EXTERN void jfree_small PP((void * object));
* These two functions are used to allocate and release large chunks of
* memory (up to the total free space designated by jmem_available).
* The interface is the same as above, except that on an 80x86 machine,
* far pointers are used. On other systems these ARE the same as above.
#ifdef NEED_FAR_POINTERS /* typically not needed except on 80x86 */
EXTERN void FAR * jget_large PP((size_t sizeofobject));
EXTERN void jfree_large PP((void FAR * object));
#define jget_large(sizeofobject) jget_small(sizeofobject)
#define jfree_large(object) jfree_small(object)
* The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
* be requested in a single call on jget_large (and jget_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 machines with flat address spaces, any large constant may be used here.
#define MAX_ALLOC_CHUNK 1000000000L
* This routine computes the total space available for allocation by
* jget_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
* jmem_available returns zero. The maximum space needed, enough to hold
* all working storage in memory, is also passed in case it is useful.
* It is OK for jmem_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, especially if jget_small space
* comes from the same pool. 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 jmem_available PP((long min_bytes_needed, long max_bytes_needed));
* 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 */
typedef struct backing_store_struct * backing_store_ptr;
typedef struct backing_store_struct {
/* Methods for reading/writing/closing this backing-store object */
METHOD(void, read_backing_store, (backing_store_ptr info,
void FAR * buffer_address,
long file_offset, long byte_count));
METHOD(void, write_backing_store, (backing_store_ptr info,
void FAR * buffer_address,
long file_offset, long byte_count));
METHOD(void, close_backing_store, (backing_store_ptr info));
/* Private fields for system-dependent backing-store management */
/* For a typical implementation with temp files, we might need: */
FILE * temp_file; /* stdio reference to temp file */
char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */
} 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 jmem_available always returns a large value, this routine can just
* take an error exit.)
EXTERN void jopen_backing_store PP((backing_store_ptr info,
long total_bytes_needed));
* These routines take care of any system-dependent initialization and
* cleanup required. The system methods struct address should be saved
* by jmem_init in case an error exit must be taken. jmem_term may assume
* that all requested memory has been freed and that all opened backing-
* store objects have been closed.
* NB: jmem_term may be called more than once, and must behave reasonably
* if that happens.
EXTERN void jmem_init PP((external_methods_ptr emethods));
EXTERN void jmem_term PP((void));