| /* |
| * jmemdos.h (jmemsys.h) |
| * |
| * Copyright (C) 1992, Thomas G. Lane. |
| * This file is part of the Independent JPEG Group's software. |
| * For conditions of distribution and use, see the accompanying README file. |
| * |
| * This include file defines the interface between the system-independent |
| * and system-dependent portions of the JPEG memory manager. (The system- |
| * independent portion is jmemmgr.c; there are several different versions |
| * of the system-dependent portion, and of this file for that matter.) |
| * |
| * This version is suitable for MS-DOS (80x86) implementations. |
| */ |
| |
| |
| /* |
| * These two functions are used to allocate and release small chunks of |
| * memory (typically the total amount requested through jget_small is |
| * no more than 20Kb or so). Behavior should be the same as for the |
| * standard library functions malloc and free; in particular, jget_small |
| * returns NULL on failure. On most systems, these ARE malloc and free. |
| * On an 80x86 machine using small-data memory model, these manage near heap. |
| */ |
| |
| EXTERN void * jget_small PP((size_t sizeofobject)); |
| EXTERN void jfree_small PP((void * object)); |
| |
| /* |
| * These two functions are used to allocate and release large chunks of |
| * memory (up to the total free space designated by jmem_available). |
| * The interface is the same as above, except that on an 80x86 machine, |
| * far pointers are used. On other systems these ARE the same as above. |
| */ |
| |
| #ifdef NEED_FAR_POINTERS /* typically not needed except on 80x86 */ |
| EXTERN void FAR * jget_large PP((size_t sizeofobject)); |
| EXTERN void jfree_large PP((void FAR * object)); |
| #else |
| #define jget_large(sizeofobject) jget_small(sizeofobject) |
| #define jfree_large(object) jfree_small(object) |
| #endif |
| |
| /* |
| * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may |
| * be requested in a single call on jget_large (and jget_small for that |
| * matter, but that case should never come into play). This macro is 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 here. |
| */ |
| |
| #define MAX_ALLOC_CHUNK 65440L /* leave room for malloc overhead */ |
| |
| /* |
| * This routine computes the total space available for allocation by |
| * jget_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 |
| * jmem_available returns zero. The maximum space needed, enough to hold |
| * all working storage in memory, is also passed in case it is useful. |
| * |
| * It is OK for jmem_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, especially if jget_small space |
| * comes from the same pool. 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 long jmem_available PP((long min_bytes_needed, long max_bytes_needed)); |
| |
| |
| /* |
| * 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 64 /* max length of a temporary file's name */ |
| |
| 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; |
| |
| typedef struct backing_store_struct * backing_store_ptr; |
| |
| typedef struct backing_store_struct { |
| /* Methods for reading/writing/closing this backing-store object */ |
| METHOD(void, read_backing_store, (backing_store_ptr info, |
| void FAR * buffer_address, |
| long file_offset, long byte_count)); |
| METHOD(void, write_backing_store, (backing_store_ptr info, |
| void FAR * buffer_address, |
| long file_offset, long byte_count)); |
| METHOD(void, close_backing_store, (backing_store_ptr info)); |
| /* Private fields for system-dependent backing-store management */ |
| /* For the MS-DOS environment, we need: */ |
| handle_union handle; /* reference to backing-store storage object */ |
| char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */ |
| } 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 jmem_available always returns a large value, this routine can just |
| * take an error exit.) |
| */ |
| |
| EXTERN void jopen_backing_store PP((backing_store_ptr info, |
| long total_bytes_needed)); |
| |
| |
| /* |
| * These routines take care of any system-dependent initialization and |
| * cleanup required. The system methods struct address should be saved |
| * by jmem_init in case an error exit must be taken. jmem_term may assume |
| * that all requested memory has been freed and that all opened backing- |
| * store objects have been closed. |
| * NB: jmem_term may be called more than once, and must behave reasonably |
| * if that happens. |
| */ |
| |
| EXTERN void jmem_init PP((external_methods_ptr emethods)); |
| EXTERN void jmem_term PP((void)); |