7 * Copyright (C) 1992-1994, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
11 * For conditions of distribution and use, see the accompanying README file.
15 * This include file defines the interface between the system-independent
17 * and system-dependent portions of the JPEG memory manager. No other
19 * modules need include it. (The system-independent portion is jmemmgr.c;
21 * there are several different versions of the system-dependent portion.)
25 * This file works as-is for the system-dependent memory managers supplied
27 * in the IJG distribution. You may need to modify it if you write a
29 * custom memory manager. If system-dependent changes are needed in
31 * this file, the best method is to #ifdef them based on a configuration
33 * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR.
41 /* Short forms of external names for systems with brain-damaged linkers. */
45 #ifdef NEED_SHORT_EXTERNAL_NAMES
47 #define jpeg_get_small jGetSmall
49 #define jpeg_free_small jFreeSmall
51 #define jpeg_get_large jGetLarge
53 #define jpeg_free_large jFreeLarge
55 #define jpeg_mem_available jMemAvail
57 #define jpeg_open_backing_store jOpenBackStore
59 #define jpeg_mem_init jMemInit
61 #define jpeg_mem_term jMemTerm
63 #endif /* NEED_SHORT_EXTERNAL_NAMES */
71 * These two functions are used to allocate and release small chunks of
73 * memory. (Typically the total amount requested through jpeg_get_small is
75 * no more than 20K or so; this will be requested in chunks of a few K each.)
77 * Behavior should be the same as for the standard library functions malloc
79 * and free; in particular, jpeg_get_small must return NULL on failure.
81 * On most systems, these ARE malloc and free. jpeg_free_small is passed the
83 * size of the object being freed, just in case it's needed.
85 * On an 80x86 machine using small-data memory model, these manage near heap.
91 EXTERN void * jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
93 EXTERN void jpeg_free_small JPP((j_common_ptr cinfo, void * object,
95 size_t sizeofobject));
101 * These two functions are used to allocate and release large chunks of
103 * memory (up to the total free space designated by jpeg_mem_available).
105 * The interface is the same as above, except that on an 80x86 machine,
107 * far pointers are used. On most other machines these are identical to
109 * the jpeg_get/free_small routines; but we keep them separate anyway,
111 * in case a different allocation strategy is desirable for large chunks.
117 EXTERN void FAR * jpeg_get_large JPP((j_common_ptr cinfo,size_t sizeofobject));
119 EXTERN void jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
121 size_t sizeofobject));
127 * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
129 * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
131 * matter, but that case should never come into play). This macro is needed
133 * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
135 * On those machines, we expect that jconfig.h will provide a proper value.
137 * On machines with 32-bit flat address spaces, any large constant may be used.
141 * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
143 * size_t and will be a multiple of sizeof(align_type).
149 #ifndef MAX_ALLOC_CHUNK /* may be overridden in jconfig.h */
151 #define MAX_ALLOC_CHUNK 1000000000L
159 * This routine computes the total space still available for allocation by
161 * jpeg_get_large. If more space than this is needed, backing store will be
163 * used. NOTE: any memory already allocated must not be counted.
167 * There is a minimum space requirement, corresponding to the minimum
169 * feasible buffer sizes; jmemmgr.c will request that much space even if
171 * jpeg_mem_available returns zero. The maximum space needed, enough to hold
173 * all working storage in memory, is also passed in case it is useful.
175 * Finally, the total space already allocated is passed. If no better
177 * method is available, cinfo->mem->max_memory_to_use - already_allocated
179 * is often a suitable calculation.
183 * It is OK for jpeg_mem_available to underestimate the space available
185 * (that'll just lead to more backing-store access than is really necessary).
187 * However, an overestimate will lead to failure. Hence it's wise to subtract
189 * a slop factor from the true available space. 5% should be enough.
193 * On machines with lots of virtual memory, any large constant may be returned.
195 * Conversely, zero may be returned to always use the minimum amount of memory.
201 EXTERN long jpeg_mem_available JPP((j_common_ptr cinfo,
203 long min_bytes_needed,
205 long max_bytes_needed,
207 long already_allocated));
215 * This structure holds whatever state is needed to access a single
217 * backing-store object. The read/write/close method pointers are called
219 * by jmemmgr.c to manipulate the backing-store object; all other fields
221 * are private to the system-dependent backing store routines.
227 #define TEMP_NAME_LENGTH 64 /* max length of a temporary file's name */
231 #ifdef USE_MSDOS_MEMMGR /* DOS-specific junk */
235 typedef unsigned short XMSH; /* type of extended-memory handles */
237 typedef unsigned short EMSH; /* type of expanded-memory handles */
243 short file_handle; /* DOS file handle if it's a temp file */
245 XMSH xms_handle; /* handle if it's a chunk of XMS */
247 EMSH ems_handle; /* handle if it's a chunk of EMS */
253 #endif /* USE_MSDOS_MEMMGR */
257 typedef struct backing_store_struct * backing_store_ptr;
261 typedef struct backing_store_struct {
263 /* Methods for reading/writing/closing this backing-store object */
265 JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
267 backing_store_ptr info,
269 void FAR * buffer_address,
271 long file_offset, long byte_count));
273 JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
275 backing_store_ptr info,
277 void FAR * buffer_address,
279 long file_offset, long byte_count));
281 JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
283 backing_store_ptr info));
287 /* Private fields for system-dependent backing-store management */
289 #ifdef USE_MSDOS_MEMMGR
291 /* For the MS-DOS manager (jmemdos.c), we need: */
293 handle_union handle; /* reference to backing-store storage object */
295 char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */
299 /* For a typical implementation with temp files, we need: */
301 FILE * temp_file; /* stdio reference to temp file */
303 char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */
307 } backing_store_info;
313 * Initial opening of a backing-store object. This must fill in the
315 * read/write/close pointers in the object. The read/write routines
317 * may take an error exit if the specified maximum file size is exceeded.
319 * (If jpeg_mem_available always returns a large value, this routine can
321 * just take an error exit.)
327 EXTERN void jpeg_open_backing_store JPP((j_common_ptr cinfo,
329 backing_store_ptr info,
331 long total_bytes_needed));
339 * These routines take care of any system-dependent initialization and
341 * cleanup required. jpeg_mem_init will be called before anything is
343 * allocated (and, therefore, nothing in cinfo is of use except the error
345 * manager pointer). It should return a suitable default value for
347 * max_memory_to_use; this may subsequently be overridden by the surrounding
349 * application. (Note that max_memory_to_use is only important if
351 * jpeg_mem_available chooses to consult it ... no one else will.)
353 * jpeg_mem_term may assume that all requested memory has been freed and that
355 * all opened backing-store objects have been closed.
361 EXTERN long jpeg_mem_init JPP((j_common_ptr cinfo));
363 EXTERN void jpeg_mem_term JPP((j_common_ptr cinfo));