The Independent JPEG Group's JPEG software v3
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+/*
+ * 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 is a "generic" skeleton that may need to be modified for particular
+ * systems. It should be usable as-is on the majority of non-MSDOS machines.
+ */
+
+
+/*
+ * 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 1000000000L
+
+/*
+ * 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 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 a typical implementation with temp files, we might need: */
+ FILE * temp_file; /* stdio reference to temp file */
+ char temp_name[TEMP_NAME_LENGTH]; /* name of temp 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));