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plt-scheme  4.2.1
jmemsys.h
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00001 /*
00002  * jmemsys.h
00003  *
00004  * Copyright (C) 1992-1997, Thomas G. Lane.
00005  * This file is part of the Independent JPEG Group's software.
00006  * For conditions of distribution and use, see the accompanying README file.
00007  *
00008  * This include file defines the interface between the system-independent
00009  * and system-dependent portions of the JPEG memory manager.  No other
00010  * modules need include it.  (The system-independent portion is jmemmgr.c;
00011  * there are several different versions of the system-dependent portion.)
00012  *
00013  * This file works as-is for the system-dependent memory managers supplied
00014  * in the IJG distribution.  You may need to modify it if you write a
00015  * custom memory manager.  If system-dependent changes are needed in
00016  * this file, the best method is to #ifdef them based on a configuration
00017  * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR
00018  * and USE_MAC_MEMMGR.
00019  */
00020 
00021 
00022 /* Short forms of external names for systems with brain-damaged linkers. */
00023 
00024 #ifdef NEED_SHORT_EXTERNAL_NAMES
00025 #define jpeg_get_small             jGetSmall
00026 #define jpeg_free_small            jFreeSmall
00027 #define jpeg_get_large             jGetLarge
00028 #define jpeg_free_large            jFreeLarge
00029 #define jpeg_mem_available  jMemAvail
00030 #define jpeg_open_backing_store    jOpenBackStore
00031 #define jpeg_mem_init              jMemInit
00032 #define jpeg_mem_term              jMemTerm
00033 #endif /* NEED_SHORT_EXTERNAL_NAMES */
00034 
00035 
00036 /*
00037  * These two functions are used to allocate and release small chunks of
00038  * memory.  (Typically the total amount requested through jpeg_get_small is
00039  * no more than 20K or so; this will be requested in chunks of a few K each.)
00040  * Behavior should be the same as for the standard library functions malloc
00041  * and free; in particular, jpeg_get_small must return NULL on failure.
00042  * On most systems, these ARE malloc and free.  jpeg_free_small is passed the
00043  * size of the object being freed, just in case it's needed.
00044  * On an 80x86 machine using small-data memory model, these manage near heap.
00045  */
00046 
00047 EXTERN(void *) jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
00048 EXTERN(void) jpeg_free_small JPP((j_common_ptr cinfo, void * object,
00049                               size_t sizeofobject));
00050 
00051 /*
00052  * These two functions are used to allocate and release large chunks of
00053  * memory (up to the total free space designated by jpeg_mem_available).
00054  * The interface is the same as above, except that on an 80x86 machine,
00055  * far pointers are used.  On most other machines these are identical to
00056  * the jpeg_get/free_small routines; but we keep them separate anyway,
00057  * in case a different allocation strategy is desirable for large chunks.
00058  */
00059 
00060 EXTERN(void FAR *) jpeg_get_large JPP((j_common_ptr cinfo,
00061                                    size_t sizeofobject));
00062 EXTERN(void) jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
00063                               size_t sizeofobject));
00064 
00065 /*
00066  * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
00067  * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
00068  * matter, but that case should never come into play).  This macro is needed
00069  * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
00070  * On those machines, we expect that jconfig.h will provide a proper value.
00071  * On machines with 32-bit flat address spaces, any large constant may be used.
00072  *
00073  * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
00074  * size_t and will be a multiple of sizeof(align_type).
00075  */
00076 
00077 #ifndef MAX_ALLOC_CHUNK            /* may be overridden in jconfig.h */
00078 #define MAX_ALLOC_CHUNK  1000000000L
00079 #endif
00080 
00081 /*
00082  * This routine computes the total space still available for allocation by
00083  * jpeg_get_large.  If more space than this is needed, backing store will be
00084  * used.  NOTE: any memory already allocated must not be counted.
00085  *
00086  * There is a minimum space requirement, corresponding to the minimum
00087  * feasible buffer sizes; jmemmgr.c will request that much space even if
00088  * jpeg_mem_available returns zero.  The maximum space needed, enough to hold
00089  * all working storage in memory, is also passed in case it is useful.
00090  * Finally, the total space already allocated is passed.  If no better
00091  * method is available, cinfo->mem->max_memory_to_use - already_allocated
00092  * is often a suitable calculation.
00093  *
00094  * It is OK for jpeg_mem_available to underestimate the space available
00095  * (that'll just lead to more backing-store access than is really necessary).
00096  * However, an overestimate will lead to failure.  Hence it's wise to subtract
00097  * a slop factor from the true available space.  5% should be enough.
00098  *
00099  * On machines with lots of virtual memory, any large constant may be returned.
00100  * Conversely, zero may be returned to always use the minimum amount of memory.
00101  */
00102 
00103 EXTERN(long) jpeg_mem_available JPP((j_common_ptr cinfo,
00104                                  long min_bytes_needed,
00105                                  long max_bytes_needed,
00106                                  long already_allocated));
00107 
00108 
00109 /*
00110  * This structure holds whatever state is needed to access a single
00111  * backing-store object.  The read/write/close method pointers are called
00112  * by jmemmgr.c to manipulate the backing-store object; all other fields
00113  * are private to the system-dependent backing store routines.
00114  */
00115 
00116 #define TEMP_NAME_LENGTH   64      /* max length of a temporary file's name */
00117 
00118 
00119 #ifdef USE_MSDOS_MEMMGR            /* DOS-specific junk */
00120 
00121 typedef unsigned short XMSH;       /* type of extended-memory handles */
00122 typedef unsigned short EMSH;       /* type of expanded-memory handles */
00123 
00124 typedef union {
00125   short file_handle;        /* DOS file handle if it's a temp file */
00126   XMSH xms_handle;          /* handle if it's a chunk of XMS */
00127   EMSH ems_handle;          /* handle if it's a chunk of EMS */
00128 } handle_union;
00129 
00130 #endif /* USE_MSDOS_MEMMGR */
00131 
00132 #ifdef USE_MAC_MEMMGR              /* Mac-specific junk */
00133 #include <Files.h>
00134 #endif /* USE_MAC_MEMMGR */
00135 
00136 
00137 typedef struct backing_store_struct * backing_store_ptr;
00138 
00139 typedef struct backing_store_struct {
00140   /* Methods for reading/writing/closing this backing-store object */
00141   JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
00142                                  backing_store_ptr info,
00143                                  void FAR * buffer_address,
00144                                  long file_offset, long byte_count));
00145   JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
00146                                   backing_store_ptr info,
00147                                   void FAR * buffer_address,
00148                                   long file_offset, long byte_count));
00149   JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
00150                                   backing_store_ptr info));
00151 
00152   /* Private fields for system-dependent backing-store management */
00153 #ifdef USE_MSDOS_MEMMGR
00154   /* For the MS-DOS manager (jmemdos.c), we need: */
00155   handle_union handle;             /* reference to backing-store storage object */
00156   char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */
00157 #else
00158 #ifdef USE_MAC_MEMMGR
00159   /* For the Mac manager (jmemmac.c), we need: */
00160   short temp_file;          /* file reference number to temp file */
00161   FSSpec tempSpec;          /* the FSSpec for the temp file */
00162   char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */
00163 #else
00164   /* For a typical implementation with temp files, we need: */
00165   FILE * temp_file;         /* stdio reference to temp file */
00166   char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */
00167 #endif
00168 #endif
00169 } backing_store_info;
00170 
00171 
00172 /*
00173  * Initial opening of a backing-store object.  This must fill in the
00174  * read/write/close pointers in the object.  The read/write routines
00175  * may take an error exit if the specified maximum file size is exceeded.
00176  * (If jpeg_mem_available always returns a large value, this routine can
00177  * just take an error exit.)
00178  */
00179 
00180 EXTERN(void) jpeg_open_backing_store JPP((j_common_ptr cinfo,
00181                                      backing_store_ptr info,
00182                                      long total_bytes_needed));
00183 
00184 
00185 /*
00186  * These routines take care of any system-dependent initialization and
00187  * cleanup required.  jpeg_mem_init will be called before anything is
00188  * allocated (and, therefore, nothing in cinfo is of use except the error
00189  * manager pointer).  It should return a suitable default value for
00190  * max_memory_to_use; this may subsequently be overridden by the surrounding
00191  * application.  (Note that max_memory_to_use is only important if
00192  * jpeg_mem_available chooses to consult it ... no one else will.)
00193  * jpeg_mem_term may assume that all requested memory has been freed and that
00194  * all opened backing-store objects have been closed.
00195  */
00196 
00197 EXTERN(long) jpeg_mem_init JPP((j_common_ptr cinfo));
00198 EXTERN(void) jpeg_mem_term JPP((j_common_ptr cinfo));