158 lines
4.2 KiB
C
158 lines
4.2 KiB
C
/*
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* jmemansi.c (jmemsys.c)
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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 file provides a simple generic implementation of the system-
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* dependent portion of the JPEG memory manager. This implementation
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* assumes that you have the ANSI-standard library routine tmpfile().
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* Also, the problem of determining the amount of memory available
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* is shoved onto the user.
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*/
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#include "jinclude.h"
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#include "jmemsys.h"
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#ifdef INCLUDES_ARE_ANSI
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#include <stdlib.h> /* to declare malloc(), free() */
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#else
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extern void * malloc PP((size_t size));
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extern void free PP((void *ptr));
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#endif
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#ifndef SEEK_SET /* pre-ANSI systems may not define this; */
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#define SEEK_SET 0 /* if not, assume 0 is correct */
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#endif
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static external_methods_ptr methods; /* saved for access to error_exit */
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static long total_used; /* total memory requested so far */
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/*
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* Memory allocation and freeing are controlled by the regular library
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* routines malloc() and free().
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*/
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GLOBAL void *
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jget_small (size_t sizeofobject)
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{
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total_used += sizeofobject;
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return (void *) malloc(sizeofobject);
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}
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GLOBAL void
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jfree_small (void * object)
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{
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free(object);
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}
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/*
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* We assume NEED_FAR_POINTERS is not defined and so the separate entry points
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* jget_large, jfree_large are not needed.
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*/
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/*
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* This routine computes the total memory space available for allocation.
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* It's impossible to do this in a portable way; our current solution is
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* to make the user tell us (with a default value set at compile time).
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* If you can actually get the available space, it's a good idea to subtract
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* a slop factor of 5% or so.
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*/
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#ifndef DEFAULT_MAX_MEM /* so can override from makefile */
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#define DEFAULT_MAX_MEM 1000000L /* default: one megabyte */
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#endif
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GLOBAL long
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jmem_available (long min_bytes_needed, long max_bytes_needed)
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{
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return methods->max_memory_to_use - total_used;
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}
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/*
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* Backing store (temporary file) management.
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* Backing store objects are only used when the value returned by
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* jmem_available is less than the total space needed. You can dispense
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* with these routines if you have plenty of virtual memory; see jmemnobs.c.
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*/
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METHODDEF void
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read_backing_store (backing_store_ptr info, void FAR * buffer_address,
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long file_offset, long byte_count)
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{
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if (fseek(info->temp_file, file_offset, SEEK_SET))
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ERREXIT(methods, "fseek failed on temporary file");
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if (JFREAD(info->temp_file, buffer_address, byte_count)
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!= (size_t) byte_count)
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ERREXIT(methods, "fread failed on temporary file");
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}
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METHODDEF void
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write_backing_store (backing_store_ptr info, void FAR * buffer_address,
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long file_offset, long byte_count)
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{
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if (fseek(info->temp_file, file_offset, SEEK_SET))
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ERREXIT(methods, "fseek failed on temporary file");
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if (JFWRITE(info->temp_file, buffer_address, byte_count)
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!= (size_t) byte_count)
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ERREXIT(methods, "fwrite failed on temporary file --- out of disk space?");
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}
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METHODDEF void
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close_backing_store (backing_store_ptr info)
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{
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fclose(info->temp_file);
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/* Since this implementation uses tmpfile() to create the file,
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* no explicit file deletion is needed.
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*/
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}
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/*
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* Initial opening of a backing-store object.
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*
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* This version uses tmpfile(), which constructs a suitable file name
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* behind the scenes. We don't have to use temp_name[] at all;
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* indeed, we can't even find out the actual name of the temp file.
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*/
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GLOBAL void
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jopen_backing_store (backing_store_ptr info, long total_bytes_needed)
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{
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if ((info->temp_file = tmpfile()) == NULL)
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ERREXIT(methods, "Failed to create temporary file");
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info->read_backing_store = read_backing_store;
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info->write_backing_store = write_backing_store;
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info->close_backing_store = close_backing_store;
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}
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/*
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* These routines take care of any system-dependent initialization and
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* cleanup required. Keep in mind that jmem_term may be called more than
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* once.
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*/
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GLOBAL void
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jmem_init (external_methods_ptr emethods)
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{
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methods = emethods; /* save struct addr for error exit access */
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emethods->max_memory_to_use = DEFAULT_MAX_MEM;
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total_used = 0;
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}
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GLOBAL void
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jmem_term (void)
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{
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/* no work */
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}
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