1/*
2 * jmemsys.h
3 *
4 * Copyright (C) 1992-1997, 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.
7 *
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.)
12 *
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.
16 */
17
18
19/* Short forms of external names for systems with brain-damaged linkers. */
20
21#ifdef NEED_SHORT_EXTERNAL_NAMES
22#define jpeg_get_small		jGetSmall
23#define jpeg_free_small		jFreeSmall
24#define jpeg_get_large		jGetLarge
25#define jpeg_free_large		jFreeLarge
26#define jpeg_mem_available	jMemAvail
27#define jpeg_open_backing_store	jOpenBackStore
28#define jpeg_mem_init		jMemInit
29#define jpeg_mem_term		jMemTerm
30#endif /* NEED_SHORT_EXTERNAL_NAMES */
31
32
33/*
34 * These two functions are used to allocate and release small chunks of
35 * memory.  (Typically the total amount requested through jpeg_get_small is
36 * no more than 20K or so; this will be requested in chunks of a few K each.)
37 * Behavior should be the same as for the standard library functions malloc
38 * and free; in particular, jpeg_get_small must return NULL on failure.
39 * On most systems, these ARE malloc and free.  jpeg_free_small is passed the
40 * size of the object being freed, just in case it's needed.
41 * On an 80x86 machine using small-data memory model, these manage near heap.
42 */
43
44EXTERN(void *) jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
45EXTERN(void) jpeg_free_small JPP((j_common_ptr cinfo, void * object,
46				  size_t sizeofobject));
47
48/*
49 * These two functions are used to allocate and release large chunks of
50 * memory (up to the total free space designated by jpeg_mem_available).
51 * The interface is the same as above, except that on an 80x86 machine,
52 * far pointers are used.  On most other machines these are identical to
53 * the jpeg_get/free_small routines; but we keep them separate anyway,
54 * in case a different allocation strategy is desirable for large chunks.
55 */
56
57EXTERN(void FAR *) jpeg_get_large JPP((j_common_ptr cinfo,
58				       size_t sizeofobject));
59EXTERN(void) jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
60				  size_t sizeofobject));
61
62/*
63 * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
64 * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
65 * matter, but that case should never come into play).  This macro is needed
66 * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
67 * On those machines, we expect that jconfig.h will provide a proper value.
68 * On machines with 32-bit flat address spaces, any large constant may be used.
69 *
70 * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
71 * size_t and will be a multiple of sizeof(align_type).
72 */
73
74#ifndef MAX_ALLOC_CHUNK		/* may be overridden in jconfig.h */
75#define MAX_ALLOC_CHUNK  1000000000L
76#endif
77
78/*
79 * This routine computes the total space still available for allocation by
80 * jpeg_get_large.  If more space than this is needed, backing store will be
81 * used.  NOTE: any memory already allocated must not be counted.
82 *
83 * There is a minimum space requirement, corresponding to the minimum
84 * feasible buffer sizes; jmemmgr.c will request that much space even if
85 * jpeg_mem_available returns zero.  The maximum space needed, enough to hold
86 * all working storage in memory, is also passed in case it is useful.
87 * Finally, the total space already allocated is passed.  If no better
88 * method is available, cinfo->mem->max_memory_to_use - already_allocated
89 * is often a suitable calculation.
90 *
91 * It is OK for jpeg_mem_available to underestimate the space available
92 * (that'll just lead to more backing-store access than is really necessary).
93 * However, an overestimate will lead to failure.  Hence it's wise to subtract
94 * a slop factor from the true available space.  5% should be enough.
95 *
96 * On machines with lots of virtual memory, any large constant may be returned.
97 * Conversely, zero may be returned to always use the minimum amount of memory.
98 */
99
100EXTERN(long) jpeg_mem_available JPP((j_common_ptr cinfo,
101				     long min_bytes_needed,
102				     long max_bytes_needed,
103				     long already_allocated));
104
105
106/*
107 * This structure holds whatever state is needed to access a single
108 * backing-store object.  The read/write/close method pointers are called
109 * by jmemmgr.c to manipulate the backing-store object; all other fields
110 * are private to the system-dependent backing store routines.
111 */
112
113#define TEMP_NAME_LENGTH   64	/* max length of a temporary file's name */
114
115typedef struct backing_store_struct * backing_store_ptr;
116
117typedef struct backing_store_struct {
118  /* Methods for reading/writing/closing this backing-store object */
119  JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
120				     backing_store_ptr info,
121				     void FAR * buffer_address,
122				     long file_offset, long byte_count));
123  JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
124				      backing_store_ptr info,
125				      void FAR * buffer_address,
126				      long file_offset, long byte_count));
127  JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
128				      backing_store_ptr info));
129
130  /* Private fields for system-dependent backing-store management */
131  /* For a typical implementation with temp files, we need: */
132  FXSYS_FILE * temp_file;		/* stdio reference to temp file */
133  char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */
134} backing_store_info;
135
136
137/*
138 * Initial opening of a backing-store object.  This must fill in the
139 * read/write/close pointers in the object.  The read/write routines
140 * may take an error exit if the specified maximum file size is exceeded.
141 * (If jpeg_mem_available always returns a large value, this routine can
142 * just take an error exit.)
143 */
144
145EXTERN(void) jpeg_open_backing_store JPP((j_common_ptr cinfo,
146					  backing_store_ptr info,
147					  long total_bytes_needed));
148
149
150/*
151 * These routines take care of any system-dependent initialization and
152 * cleanup required.  jpeg_mem_init will be called before anything is
153 * allocated (and, therefore, nothing in cinfo is of use except the error
154 * manager pointer).  It should return a suitable default value for
155 * max_memory_to_use; this may subsequently be overridden by the surrounding
156 * application.  (Note that max_memory_to_use is only important if
157 * jpeg_mem_available chooses to consult it ... no one else will.)
158 * jpeg_mem_term may assume that all requested memory has been freed and that
159 * all opened backing-store objects have been closed.
160 */
161
162EXTERN(long) jpeg_mem_init JPP((j_common_ptr cinfo));
163EXTERN(void) jpeg_mem_term JPP((j_common_ptr cinfo));
164