Thomas G. Lane | 4a6b730 | 1992-03-17 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * jmemsys.h |
| 3 | * |
| 4 | * Copyright (C) 1992, 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. (The system- |
| 10 | * independent portion is jmemmgr.c; there are several different versions |
| 11 | * of the system-dependent portion, and of this file for that matter.) |
| 12 | * |
| 13 | * This is a "generic" skeleton that may need to be modified for particular |
| 14 | * systems. It should be usable as-is on the majority of non-MSDOS machines. |
| 15 | */ |
| 16 | |
| 17 | |
| 18 | /* |
| 19 | * These two functions are used to allocate and release small chunks of |
| 20 | * memory (typically the total amount requested through jget_small is |
| 21 | * no more than 20Kb or so). Behavior should be the same as for the |
| 22 | * standard library functions malloc and free; in particular, jget_small |
| 23 | * returns NULL on failure. On most systems, these ARE malloc and free. |
| 24 | * On an 80x86 machine using small-data memory model, these manage near heap. |
| 25 | */ |
| 26 | |
| 27 | EXTERN void * jget_small PP((size_t sizeofobject)); |
| 28 | EXTERN void jfree_small PP((void * object)); |
| 29 | |
| 30 | /* |
| 31 | * These two functions are used to allocate and release large chunks of |
| 32 | * memory (up to the total free space designated by jmem_available). |
| 33 | * The interface is the same as above, except that on an 80x86 machine, |
| 34 | * far pointers are used. On other systems these ARE the same as above. |
| 35 | */ |
| 36 | |
| 37 | #ifdef NEED_FAR_POINTERS /* typically not needed except on 80x86 */ |
| 38 | EXTERN void FAR * jget_large PP((size_t sizeofobject)); |
| 39 | EXTERN void jfree_large PP((void FAR * object)); |
| 40 | #else |
| 41 | #define jget_large(sizeofobject) jget_small(sizeofobject) |
| 42 | #define jfree_large(object) jfree_small(object) |
| 43 | #endif |
| 44 | |
| 45 | /* |
| 46 | * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may |
| 47 | * be requested in a single call on jget_large (and jget_small for that |
| 48 | * matter, but that case should never come into play). This macro is needed |
| 49 | * to model the 64Kb-segment-size limit of far addressing on 80x86 machines. |
| 50 | * On machines with flat address spaces, any large constant may be used here. |
| 51 | */ |
| 52 | |
| 53 | #define MAX_ALLOC_CHUNK 1000000000L |
| 54 | |
| 55 | /* |
| 56 | * This routine computes the total space available for allocation by |
| 57 | * jget_large. If more space than this is needed, backing store will be used. |
| 58 | * NOTE: any memory already allocated must not be counted. |
| 59 | * |
| 60 | * There is a minimum space requirement, corresponding to the minimum |
| 61 | * feasible buffer sizes; jmemmgr.c will request that much space even if |
| 62 | * jmem_available returns zero. The maximum space needed, enough to hold |
| 63 | * all working storage in memory, is also passed in case it is useful. |
| 64 | * |
| 65 | * It is OK for jmem_available to underestimate the space available (that'll |
| 66 | * just lead to more backing-store access than is really necessary). |
| 67 | * However, an overestimate will lead to failure. Hence it's wise to subtract |
| 68 | * a slop factor from the true available space, especially if jget_small space |
| 69 | * comes from the same pool. 5% should be enough. |
| 70 | * |
| 71 | * On machines with lots of virtual memory, any large constant may be returned. |
| 72 | * Conversely, zero may be returned to always use the minimum amount of memory. |
| 73 | */ |
| 74 | |
| 75 | EXTERN long jmem_available PP((long min_bytes_needed, long max_bytes_needed)); |
| 76 | |
| 77 | |
| 78 | /* |
| 79 | * This structure holds whatever state is needed to access a single |
| 80 | * backing-store object. The read/write/close method pointers are called |
| 81 | * by jmemmgr.c to manipulate the backing-store object; all other fields |
| 82 | * are private to the system-dependent backing store routines. |
| 83 | */ |
| 84 | |
| 85 | #define TEMP_NAME_LENGTH 64 /* max length of a temporary file's name */ |
| 86 | |
| 87 | typedef struct backing_store_struct * backing_store_ptr; |
| 88 | |
| 89 | typedef struct backing_store_struct { |
| 90 | /* Methods for reading/writing/closing this backing-store object */ |
| 91 | METHOD(void, read_backing_store, (backing_store_ptr info, |
| 92 | void FAR * buffer_address, |
| 93 | long file_offset, long byte_count)); |
| 94 | METHOD(void, write_backing_store, (backing_store_ptr info, |
| 95 | void FAR * buffer_address, |
| 96 | long file_offset, long byte_count)); |
| 97 | METHOD(void, close_backing_store, (backing_store_ptr info)); |
| 98 | /* Private fields for system-dependent backing-store management */ |
| 99 | /* For a typical implementation with temp files, we might need: */ |
| 100 | FILE * temp_file; /* stdio reference to temp file */ |
| 101 | char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */ |
| 102 | } backing_store_info; |
| 103 | |
| 104 | /* |
| 105 | * Initial opening of a backing-store object. This must fill in the |
| 106 | * read/write/close pointers in the object. The read/write routines |
| 107 | * may take an error exit if the specified maximum file size is exceeded. |
| 108 | * (If jmem_available always returns a large value, this routine can just |
| 109 | * take an error exit.) |
| 110 | */ |
| 111 | |
| 112 | EXTERN void jopen_backing_store PP((backing_store_ptr info, |
| 113 | long total_bytes_needed)); |
| 114 | |
| 115 | |
| 116 | /* |
| 117 | * These routines take care of any system-dependent initialization and |
| 118 | * cleanup required. The system methods struct address should be saved |
| 119 | * by jmem_init in case an error exit must be taken. jmem_term may assume |
| 120 | * that all requested memory has been freed and that all opened backing- |
| 121 | * store objects have been closed. |
| 122 | * NB: jmem_term may be called more than once, and must behave reasonably |
| 123 | * if that happens. |
| 124 | */ |
| 125 | |
| 126 | EXTERN void jmem_init PP((external_methods_ptr emethods)); |
| 127 | EXTERN void jmem_term PP((void)); |