147 lines
6.2 KiB
C
147 lines
6.2 KiB
C
/*
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$Log: S:\jpeg32\inc\jmemsys.h_v $
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*
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* Rev 1.0 02 May 1995 16:16:08 JAR
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* Initial entry
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*
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* Rev 1.0 02 May 1995 15:57:46 JAR
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* Initial entry
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*/
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/*
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* jmemsys.h
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*
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* Copyright (C) 1992, 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. (The system-
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* independent portion is jmemmgr.c; there are several different versions
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* of the system-dependent portion, and of this file for that matter.)
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*
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* This is a "generic" skeleton that may need to be modified for particular
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* systems. It should be usable as-is on the majority of non-MSDOS machines.
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*/
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/*
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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 jget_small is
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* no more than 20Kb or so). Behavior should be the same as for the
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* standard library functions malloc and free; in particular, jget_small
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* returns NULL on failure. On most systems, these ARE malloc and free.
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* On an 80x86 machine using small-data memory model, these manage near heap.
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*/
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EXTERN void * jget_small PP((size_t sizeofobject));
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EXTERN void jfree_small PP((void * object));
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EXTERN void * jget_small_c PP((size_t sizeofobject));
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/*
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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 jmem_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 other systems these ARE the same as above.
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*/
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/*#ifdef NEED_FAR_POINTERS typically not needed except on 80x86 */
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/* EXTERN void FAR * jget_large PP((size_t sizeofobject));
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EXTERN void FAR * jget_large_c PP((size_t sizeofobject));
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EXTERN void jfree_large PP((void FAR * object));
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#else */
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/*#define jget_large(sizeofobject) jget_small(sizeofobject)
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#define jget_large_c(sizeofobject) jget_small_c(sizeofobject)
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#define jfree_large(object) jfree_small(object) */
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EXTERN void FAR * jget_large PP((size_t sizeofobject));
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EXTERN void FAR * jget_large_c PP((size_t sizeofobject));
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EXTERN void jfree_large PP((void FAR * object));
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/* #endif */
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/*
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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 on jget_large (and jget_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 machines with flat address spaces, any large constant may be used here.
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*/
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#define MAX_ALLOC_CHUNK 1000000000L
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/*
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* This routine computes the total space available for allocation by
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* jget_large. If more space than this is needed, backing store will be used.
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* 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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* jmem_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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*
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* It is OK for jmem_available to underestimate the space available (that'll
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* 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, especially if jget_small space
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* comes from the same pool. 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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*/
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EXTERN long jmem_available PP((long min_bytes_needed, long max_bytes_needed));
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EXTERN long jmem_available_c PP((long min_bytes_needed, long max_bytes_needed));
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/*
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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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*/
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#define TEMP_NAME_LENGTH 64 /* max length of a temporary file's name */
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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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METHOD(void, read_backing_store, (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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METHOD(void, write_backing_store, (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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METHOD(void, close_backing_store, (backing_store_ptr info));
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/* Private fields for system-dependent backing-store management */
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/* For a typical implementation with temp files, we might 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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} backing_store_info;
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/*
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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 jmem_available always returns a large value, this routine can just
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* take an error exit.)
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*/
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EXTERN void jopen_backing_store PP((backing_store_ptr info,
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long total_bytes_needed));
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/*
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* These routines take care of any system-dependent initialization and
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* cleanup required. The system methods struct address should be saved
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* by jmem_init in case an error exit must be taken. jmem_term may assume
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* that all requested memory has been freed and that all opened backing-
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* store objects have been closed.
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* NB: jmem_term may be called more than once, and must behave reasonably
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* if that happens.
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*/
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EXTERN void jmem_init PP((external_methods_ptr emethods));
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EXTERN void jmem_term PP((void));
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EXTERN void jmem_init_c PP((external_methods_ptr emethods));
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