166 lines
7.8 KiB
C
166 lines
7.8 KiB
C
// * jmemsys.h
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// *
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// * Copyright (C) 1992-1994, Thomas G. Lane.
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// * This file is part of the Independent JPEG Group's software.
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// * For conditions of distribution and use, see the accompanying README file.
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// *
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// * This include file defines the interface between the system-independent
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// * and system-dependent portions of the JPEG memory manager. No other
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// * modules need include it. (The system-independent portion is jmemmgr.c;
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// * there are several different versions of the system-dependent portion.)
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// *
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// * This file works as-is for the system-dependent memory managers supplied
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// * in the IJG distribution. You may need to modify it if you write a
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// * custom memory manager. If system-dependent changes are needed in
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// * this file, the best method is to #ifdef them based on a configuration
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// * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR.
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// Short forms of external names for systems with brain-damaged linkers.
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#ifdef NEED_SHORT_EXTERNAL_NAMES
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#define jpeg_get_small jGetSmall
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#define jpeg_free_small jFreeSmall
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#define jpeg_get_large jGetLarge
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#define jpeg_free_large jFreeLarge
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#define jpeg_mem_available jMemAvail
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#define jpeg_open_backing_store jOpenBackStore
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#define jpeg_mem_init jMemInit
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#define jpeg_mem_term jMemTerm
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#endif // NEED_SHORT_EXTERNAL_NAMES
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// * These two functions are used to allocate and release small chunks of
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// * memory. (Typically the total amount requested through jpeg_get_small is
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// * no more than 20K or so; this will be requested in chunks of a few K each.)
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// * Behavior should be the same as for the standard library functions malloc
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// * and free; in particular, jpeg_get_small must return NULL on failure.
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// * On most systems, these ARE malloc and free. jpeg_free_small is passed the
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// * size of the object being freed, just in case it's needed.
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// * On an 80x86 machine using small-data memory model, these manage near heap.
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EXTERN void * jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
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EXTERN void jpeg_free_small JPP((j_common_ptr cinfo, void * object,
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size_t sizeofobject));
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// * These two functions are used to allocate and release large chunks of
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// * memory (up to the total free space designated by jpeg_mem_available).
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// * The interface is the same as above, except that on an 80x86 machine,
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// * far pointers are used. On most other machines these are identical to
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// * the jpeg_get/free_small routines; but we keep them separate anyway,
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// * in case a different allocation strategy is desirable for large chunks.
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EXTERN void FAR * jpeg_get_large JPP((j_common_ptr cinfo,size_t sizeofobject));
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EXTERN void jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
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size_t sizeofobject));
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// * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
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// * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
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// * matter, but that case should never come into play). This macro is needed
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// * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
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// * On those machines, we expect that jconfig.h will provide a proper value.
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// * On machines with 32-bit flat address spaces, any large constant may be used.
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// *
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// * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
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// * size_t and will be a multiple of sizeof(align_type).
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#ifndef MAX_ALLOC_CHUNK // may be overridden in jconfig.h
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#define MAX_ALLOC_CHUNK 1000000000L
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#endif
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// * This routine computes the total space still available for allocation by
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// * jpeg_get_large. If more space than this is needed, backing store will be
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// * used. NOTE: any memory already allocated must not be counted.
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// *
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// * There is a minimum space requirement, corresponding to the minimum
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// * feasible buffer sizes; jmemmgr.c will request that much space even if
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// * jpeg_mem_available returns zero. The maximum space needed, enough to hold
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// * all working storage in memory, is also passed in case it is useful.
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// * Finally, the total space already allocated is passed. If no better
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// * method is available, cinfo->mem->max_memory_to_use - already_allocated
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// * is often a suitable calculation.
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// *
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// * It is OK for jpeg_mem_available to underestimate the space available
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// * (that'll just lead to more backing-store access than is really necessary).
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// * However, an overestimate will lead to failure. Hence it's wise to subtract
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// * a slop factor from the true available space. 5% should be enough.
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// *
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// * On machines with lots of virtual memory, any large constant may be returned.
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// * Conversely, zero may be returned to always use the minimum amount of memory.
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EXTERN LONG jpeg_mem_available JPP((j_common_ptr cinfo,
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LONG min_bytes_needed,
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LONG max_bytes_needed,
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LONG already_allocated));
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// * This structure holds whatever state is needed to access a single
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// * backing-store object. The read/write/close method pointers are called
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// * by jmemmgr.c to manipulate the backing-store object; all other fields
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// * are private to the system-dependent backing store routines.
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#define TEMP_NAME_LENGTH 64 // max length of a temporary file's name
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#ifdef USE_MSDOS_MEMMGR // DOS-specific junk
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typedef unsigned short XMSH; // type of extended-memory handles
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typedef unsigned short EMSH; // type of expanded-memory handles
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typedef union {
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short file_handle; // DOS file handle if it's a temp file
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XMSH xms_handle; // handle if it's a chunk of XMS
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EMSH ems_handle; // handle if it's a chunk of EMS
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} handle_union;
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#endif // USE_MSDOS_MEMMGR
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typedef struct backing_store_struct * backing_store_ptr;
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typedef struct backing_store_struct {
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// Methods for reading/writing/closing this backing-store object
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JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
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backing_store_ptr info,
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void FAR * buffer_address,
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LONG file_offset, LONG byte_count));
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JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
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backing_store_ptr info,
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void FAR * buffer_address,
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LONG file_offset, LONG byte_count));
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JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
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backing_store_ptr info));
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// Private fields for system-dependent backing-store management
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#ifdef USE_MSDOS_MEMMGR
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// For the MS-DOS manager (jmemdos.c), we need:
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handle_union handle; // reference to backing-store storage object
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char temp_name[TEMP_NAME_LENGTH]; // name if it's a file
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#else
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// For a typical implementation with temp files, we need:
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FILE * temp_file; // stdio reference to temp file
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char temp_name[TEMP_NAME_LENGTH]; // name of temp file
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#endif
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} backing_store_info;
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// * Initial opening of a backing-store object. This must fill in the
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// * read/write/close pointers in the object. The read/write routines
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// * may take an error exit if the specified maximum file size is exceeded.
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// * (If jpeg_mem_available always returns a large value, this routine can
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// * just take an error exit.)
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EXTERN void jpeg_open_backing_store JPP((j_common_ptr cinfo,
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backing_store_ptr info,
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LONG total_bytes_needed));
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// * These routines take care of any system-dependent initialization and
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// * cleanup required. jpeg_mem_init will be called before anything is
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// * allocated (and, therefore, nothing in cinfo is of use except the error
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// * manager pointer). It should return a suitable default value for
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// * max_memory_to_use; this may subsequently be overridden by the surrounding
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// * application. (Note that max_memory_to_use is only important if
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// * jpeg_mem_available chooses to consult it ... no one else will.)
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// * jpeg_mem_term may assume that all requested memory has been freed and that
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// * all opened backing-store objects have been closed.
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EXTERN LONG jpeg_mem_init JPP((j_common_ptr cinfo));
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EXTERN void jpeg_mem_term JPP((j_common_ptr cinfo));
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