jmemsys.h (7820B)
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 */ 100 101 EXTERN long jpeg_mem_available JPP((j_common_ptr cinfo, 102 long min_bytes_needed, 103 long max_bytes_needed, 104 long already_allocated)); 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 */ 128 129 typedef struct backing_store_struct * backing_store_ptr; 130 131 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)); 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 154 } backing_store_info; 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 */ 163 164 EXTERN void jpeg_open_backing_store JPP((j_common_ptr cinfo, 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));