/* * jmemsys.h * * This file was part of the Independent JPEG Group's software: * Copyright (C) 1992-1997, Thomas G. Lane. * It was modified by The libjpeg-turbo Project to include only code and * information relevant to libjpeg-turbo. * For conditions of distribution and use, see the accompanying README.ijg * file. * * This include file defines the interface between the system-independent * and system-dependent portions of the JPEG memory manager. No other * modules need include it. (The system-independent portion is jmemmgr.c; * there are several different versions of the system-dependent portion.) * * This file works as-is for the system-dependent memory managers supplied * in the IJG distribution. You may need to modify it if you write a * custom memory manager. If system-dependent changes are needed in * this file, the best method is to #ifdef them based on a configuration * symbol supplied in jconfig.h. */ /* * These two functions are used to allocate and release small chunks of * memory. (Typically the total amount requested through jpeg_get_small is * no more than 20K or so; this will be requested in chunks of a few K each.) * Behavior should be the same as for the standard library functions malloc * and free; in particular, jpeg_get_small must return NULL on failure. * On most systems, these ARE malloc and free. jpeg_free_small is passed the * size of the object being freed, just in case it's needed. */ EXTERN(void *) jpeg_get_small(j_common_ptr cinfo, size_t sizeofobject); EXTERN(void) jpeg_free_small(j_common_ptr cinfo, void *object, size_t sizeofobject); /* * These two functions are used to allocate and release large chunks of * memory (up to the total free space designated by jpeg_mem_available). * These are identical to the jpeg_get/free_small routines; but we keep them * separate anyway, in case a different allocation strategy is desirable for * large chunks. */ EXTERN(void *) jpeg_get_large(j_common_ptr cinfo, size_t sizeofobject); EXTERN(void) jpeg_free_large(j_common_ptr cinfo, void *object, size_t sizeofobject); /* * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may * be requested in a single call to jpeg_get_large (and jpeg_get_small for that * matter, but that case should never come into play). This macro was needed * to model the 64Kb-segment-size limit of far addressing on 80x86 machines. * On machines with flat address spaces, any large constant may be used. * * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type * size_t and will be a multiple of sizeof(align_type). */ #ifndef MAX_ALLOC_CHUNK /* may be overridden in jconfig.h */ #define MAX_ALLOC_CHUNK … #endif /* * This routine computes the total space still available for allocation by * jpeg_get_large. If more space than this is needed, backing store will be * used. NOTE: any memory already allocated must not be counted. * * There is a minimum space requirement, corresponding to the minimum * feasible buffer sizes; jmemmgr.c will request that much space even if * jpeg_mem_available returns zero. The maximum space needed, enough to hold * all working storage in memory, is also passed in case it is useful. * Finally, the total space already allocated is passed. If no better * method is available, cinfo->mem->max_memory_to_use - already_allocated * is often a suitable calculation. * * It is OK for jpeg_mem_available to underestimate the space available * (that'll just lead to more backing-store access than is really necessary). * However, an overestimate will lead to failure. Hence it's wise to subtract * a slop factor from the true available space. 5% should be enough. * * On machines with lots of virtual memory, any large constant may be returned. * Conversely, zero may be returned to always use the minimum amount of memory. */ EXTERN(size_t) jpeg_mem_available(j_common_ptr cinfo, size_t min_bytes_needed, size_t max_bytes_needed, size_t already_allocated); /* * This structure holds whatever state is needed to access a single * backing-store object. The read/write/close method pointers are called * by jmemmgr.c to manipulate the backing-store object; all other fields * are private to the system-dependent backing store routines. */ #define TEMP_NAME_LENGTH … #ifdef USE_MSDOS_MEMMGR /* DOS-specific junk */ typedef unsigned short XMSH; /* type of extended-memory handles */ typedef unsigned short EMSH; /* type of expanded-memory handles */ typedef union { short file_handle; /* DOS file handle if it's a temp file */ XMSH xms_handle; /* handle if it's a chunk of XMS */ EMSH ems_handle; /* handle if it's a chunk of EMS */ } handle_union; #endif /* USE_MSDOS_MEMMGR */ #ifdef USE_MAC_MEMMGR /* Mac-specific junk */ #include <Files.h> #endif /* USE_MAC_MEMMGR */ backing_store_ptr; backing_store_info; /* * Initial opening of a backing-store object. This must fill in the * read/write/close pointers in the object. The read/write routines * may take an error exit if the specified maximum file size is exceeded. * (If jpeg_mem_available always returns a large value, this routine can * just take an error exit.) */ EXTERN(void) jpeg_open_backing_store(j_common_ptr cinfo, backing_store_ptr info, long total_bytes_needed); /* * These routines take care of any system-dependent initialization and * cleanup required. jpeg_mem_init will be called before anything is * allocated (and, therefore, nothing in cinfo is of use except the error * manager pointer). It should return a suitable default value for * max_memory_to_use; this may subsequently be overridden by the surrounding * application. (Note that max_memory_to_use is only important if * jpeg_mem_available chooses to consult it ... no one else will.) * jpeg_mem_term may assume that all requested memory has been freed and that * all opened backing-store objects have been closed. */ EXTERN(long) jpeg_mem_init(j_common_ptr cinfo); EXTERN(void) jpeg_mem_term(j_common_ptr cinfo);
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