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      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 
     44 EXTERN(void *) jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
     45 EXTERN(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 
     57 EXTERN(void FAR *) jpeg_get_large JPP((j_common_ptr cinfo,
     58 				       size_t sizeofobject));
     59 EXTERN(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 
    100 EXTERN(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 
    115 typedef struct backing_store_struct * backing_store_ptr;
    116 
    117 typedef 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 
    145 EXTERN(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 
    162 EXTERN(long) jpeg_mem_init JPP((j_common_ptr cinfo));
    163 EXTERN(void) jpeg_mem_term JPP((j_common_ptr cinfo));
    164