4 * Copyright (C) 1992-1994, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
8 * This include file defines the interface between the system-independent
9 * and system-dependent portions of the JPEG memory manager. No other
10 * modules need include it. (The system-independent portion is jmemmgr.c;
11 * there are several different versions of the system-dependent portion.)
13 * This file works as-is for the system-dependent memory managers supplied
14 * in the IJG distribution. You may need to modify it if you write a
15 * custom memory manager. If system-dependent changes are needed in
16 * this file, the best method is to #ifdef them based on a configuration
17 * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR.
21 /* Short forms of external names for systems with brain-damaged linkers. */
23 #ifdef NEED_SHORT_EXTERNAL_NAMES
24 #define jpeg_get_small jGetSmall
25 #define jpeg_free_small jFreeSmall
26 #define jpeg_get_large jGetLarge
27 #define jpeg_free_large jFreeLarge
28 #define jpeg_mem_available jMemAvail
29 #define jpeg_open_backing_store jOpenBackStore
30 #define jpeg_mem_init jMemInit
31 #define jpeg_mem_term jMemTerm
32 #endif /* NEED_SHORT_EXTERNAL_NAMES */
36 * These two functions are used to allocate and release small chunks of
37 * memory. (Typically the total amount requested through jpeg_get_small is
38 * no more than 20K or so; this will be requested in chunks of a few K each.)
39 * Behavior should be the same as for the standard library functions malloc
40 * and free; in particular, jpeg_get_small must return NULL on failure.
41 * On most systems, these ARE malloc and free. jpeg_free_small is passed the
42 * size of the object being freed, just in case it's needed.
43 * On an 80x86 machine using small-data memory model, these manage near heap.
46 EXTERN void * jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
47 EXTERN void jpeg_free_small JPP((j_common_ptr cinfo, void * object,
48 size_t sizeofobject));
51 * These two functions are used to allocate and release large chunks of
52 * memory (up to the total free space designated by jpeg_mem_available).
53 * The interface is the same as above, except that on an 80x86 machine,
54 * far pointers are used. On most other machines these are identical to
55 * the jpeg_get/free_small routines; but we keep them separate anyway,
56 * in case a different allocation strategy is desirable for large chunks.
59 EXTERN void FAR * jpeg_get_large JPP((j_common_ptr cinfo,size_t sizeofobject));
60 EXTERN void jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
61 size_t sizeofobject));
64 * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
65 * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
66 * matter, but that case should never come into play). This macro is needed
67 * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
68 * On those machines, we expect that jconfig.h will provide a proper value.
69 * On machines with 32-bit flat address spaces, any large constant may be used.
71 * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
72 * size_t and will be a multiple of sizeof(align_type).
75 #ifndef MAX_ALLOC_CHUNK /* may be overridden in jconfig.h */
76 #define MAX_ALLOC_CHUNK 1000000000L
80 * This routine computes the total space still available for allocation by
81 * jpeg_get_large. If more space than this is needed, backing store will be
82 * used. NOTE: any memory already allocated must not be counted.
84 * There is a minimum space requirement, corresponding to the minimum
85 * feasible buffer sizes; jmemmgr.c will request that much space even if
86 * jpeg_mem_available returns zero. The maximum space needed, enough to hold
87 * all working storage in memory, is also passed in case it is useful.
88 * Finally, the total space already allocated is passed. If no better
89 * method is available, cinfo->mem->max_memory_to_use - already_allocated
90 * is often a suitable calculation.
92 * It is OK for jpeg_mem_available to underestimate the space available
93 * (that'll just lead to more backing-store access than is really necessary).
94 * However, an overestimate will lead to failure. Hence it's wise to subtract
95 * a slop factor from the true available space. 5% should be enough.
97 * On machines with lots of virtual memory, any large constant may be returned.
98 * Conversely, zero may be returned to always use the minimum amount of memory.
101 EXTERN long jpeg_mem_available JPP((j_common_ptr cinfo,
102 long min_bytes_needed,
103 long max_bytes_needed,
104 long already_allocated));
108 * This structure holds whatever state is needed to access a single
109 * backing-store object. The read/write/close method pointers are called
110 * by jmemmgr.c to manipulate the backing-store object; all other fields
111 * are private to the system-dependent backing store routines.
114 #define TEMP_NAME_LENGTH 64 /* max length of a temporary file's name */
116 #ifdef USE_MSDOS_MEMMGR /* DOS-specific junk */
118 typedef unsigned short XMSH; /* type of extended-memory handles */
119 typedef unsigned short EMSH; /* type of expanded-memory handles */
122 short file_handle; /* DOS file handle if it's a temp file */
123 XMSH xms_handle; /* handle if it's a chunk of XMS */
124 EMSH ems_handle; /* handle if it's a chunk of EMS */
127 #endif /* USE_MSDOS_MEMMGR */
129 typedef struct backing_store_struct * backing_store_ptr;
131 typedef struct backing_store_struct {
132 /* Methods for reading/writing/closing this backing-store object */
133 JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
134 backing_store_ptr info,
135 void FAR * buffer_address,
136 long file_offset, long byte_count));
137 JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
138 backing_store_ptr info,
139 void FAR * buffer_address,
140 long file_offset, long byte_count));
141 JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
142 backing_store_ptr info));
144 /* Private fields for system-dependent backing-store management */
145 #ifdef USE_MSDOS_MEMMGR
146 /* For the MS-DOS manager (jmemdos.c), we need: */
147 handle_union handle; /* reference to backing-store storage object */
148 char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */
150 /* For a typical implementation with temp files, we need: */
151 FILE * temp_file; /* stdio reference to temp file */
152 char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */
154 } backing_store_info;
157 * Initial opening of a backing-store object. This must fill in the
158 * read/write/close pointers in the object. The read/write routines
159 * may take an error exit if the specified maximum file size is exceeded.
160 * (If jpeg_mem_available always returns a large value, this routine can
161 * just take an error exit.)
164 EXTERN void jpeg_open_backing_store JPP((j_common_ptr cinfo,
165 backing_store_ptr info,
166 long total_bytes_needed));
170 * These routines take care of any system-dependent initialization and
171 * cleanup required. jpeg_mem_init will be called before anything is
172 * allocated (and, therefore, nothing in cinfo is of use except the error
173 * manager pointer). It should return a suitable default value for
174 * max_memory_to_use; this may subsequently be overridden by the surrounding
175 * application. (Note that max_memory_to_use is only important if
176 * jpeg_mem_available chooses to consult it ... no one else will.)
177 * jpeg_mem_term may assume that all requested memory has been freed and that
178 * all opened backing-store objects have been closed.
181 EXTERN long jpeg_mem_init JPP((j_common_ptr cinfo));
182 EXTERN void jpeg_mem_term JPP((j_common_ptr cinfo));