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jmemsys.h
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1 /*
2  * jmemsys.h
3  *
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.
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. 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.
18  */
19 
20 
21 /* Short forms of external names for systems with brain-damaged linkers. */
22 
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 */
33 
34 
35 /*
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.
44  */
45 
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));
49 
50 /*
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.
57  */
58 
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));
62 
63 /*
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.
70  *
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).
73  */
74 
75 #ifndef MAX_ALLOC_CHUNK /* may be overridden in jconfig.h */
76 #define MAX_ALLOC_CHUNK 1000000000L
77 #endif
78 
79 /*
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.
83  *
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.
91  *
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.
96  *
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.
99  */
100 
102  long min_bytes_needed,
103  long max_bytes_needed,
104  long already_allocated));
105 
106 
107 /*
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.
112  */
113 
114 #define TEMP_NAME_LENGTH 64 /* max length of a temporary file's name */
115 
116 #ifdef USE_MSDOS_MEMMGR /* DOS-specific junk */
117 
118 typedef unsigned short XMSH; /* type of extended-memory handles */
119 typedef unsigned short EMSH; /* type of expanded-memory handles */
120 
121 typedef union {
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 */
125 } handle_union;
126 
127 #endif /* USE_MSDOS_MEMMGR */
128 
130 
131 typedef struct backing_store_struct {
132  /* Methods for reading/writing/closing this backing-store object */
134  backing_store_ptr info,
135  void FAR * buffer_address,
136  long file_offset, long byte_count));
138  backing_store_ptr info,
139  void FAR * buffer_address,
140  long file_offset, long byte_count));
142  backing_store_ptr info));
143 
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 */
149 #else
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 */
153 #endif
155 
156 /*
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.)
162  */
163 
165  backing_store_ptr info,
166  long total_bytes_needed));
167 
168 
169 /*
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.
179  */
180 
181 EXTERN long jpeg_mem_init JPP((j_common_ptr cinfo));
182 EXTERN void jpeg_mem_term JPP((j_common_ptr cinfo));
JMETHOD(void, read_backing_store,(j_common_ptr cinfo, backing_store_ptr info, void FAR *buffer_address, long file_offset, long byte_count))
struct backing_store_struct * backing_store_ptr
Definition: jmemsys.h:129
char temp_name[TEMP_NAME_LENGTH]
Definition: jmemsys.h:152
GLOBAL void jpeg_mem_term(j_common_ptr cinfo)
Definition: jmemansi.c:164
GLOBAL void jpeg_free_large(j_common_ptr cinfo, void FAR *object, size_t sizeofobject)
Definition: jmemansi.c:62
GLOBAL long jpeg_mem_init(j_common_ptr cinfo)
Definition: jmemansi.c:158
GLOBAL void jpeg_free_small(j_common_ptr cinfo, void *object, size_t sizeofobject)
Definition: jmemansi.c:42
struct backing_store_struct backing_store_info
GLOBAL void jpeg_open_backing_store(j_common_ptr cinfo, backing_store_ptr info, long total_bytes_needed)
Definition: jmemansi.c:141
GLOBAL long jpeg_mem_available(j_common_ptr cinfo, long min_bytes_needed, long max_bytes_needed, long already_allocated)
Definition: jmemansi.c:81
#define TEMP_NAME_LENGTH
Definition: jmemsys.h:114
GLOBAL void * jpeg_get_small(j_common_ptr cinfo, size_t sizeofobject)
Definition: jmemansi.c:36
#define FAR
Definition: jmorecfg.h:205
EXTERN void *jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject))
METHODDEF void close_backing_store(j_common_ptr cinfo, backing_store_ptr info)
Definition: jmemansi.c:123
METHODDEF void write_backing_store(j_common_ptr cinfo, backing_store_ptr info, void FAR *buffer_address, long file_offset, long byte_count)
Definition: jmemansi.c:110
METHODDEF void read_backing_store(j_common_ptr cinfo, backing_store_ptr info, void FAR *buffer_address, long file_offset, long byte_count)
Definition: jmemansi.c:97
GLOBAL void FAR * jpeg_get_large(j_common_ptr cinfo, size_t sizeofobject)
Definition: jmemansi.c:56
#define EXTERN
Definition: jmorecfg.h:191