/*
 * jmemansi.c  (jmemsys.c)
 *
 * 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 file provides a simple generic implementation of the system-
 * dependent portion of the JPEG memory manager.  This implementation
 * assumes that you have the ANSI-standard library routine tmpfile().
 * Also, the problem of determining the amount of memory available
 * is shoved onto the user.
 */

#include "jinclude.h"
#include "jmemsys.h"
#include "FYEOMem.h"

static external_methods_ptr methods;    /* saved for access to error_exit */

/*
 * Memory allocation and freeing are controlled by the regular library
 * routines malloc() and free().
 */

GLOBAL void *
    jget_small(size_t sizeofobject)
{
   return(FYEO_alloc(sizeofobject));
}

GLOBAL void
    jfree_small(void *object)
{
   FYEO_free(object);
}

/*
 * We assume NEED_FAR_POINTERS is not defined and so the separate entry points
 * jget_large, jfree_large are not needed.
 */


/*
 * This routine computes the total memory space available for allocation.
 * It's impossible to do this in a portable way; our current solution is
 * to make the user tell us (with a default value set at compile time).
 * If you can actually get the available space, it's a good idea to subtract
 * a slop factor of 5% or so.
 */

#ifndef DEFAULT_MAX_MEM /* so can override from makefile */
#define DEFAULT_MAX_MEM         1000000L        /* default: one megabyte */
#endif

GLOBAL long
    jmem_available(long min_bytes_needed, long max_bytes_needed)
{
   return((long)FYEO_mem_available());
}


/*
 * Backing store (temporary file) management.
 * Backing store objects are only used when the value returned by
 * jmem_available is less than the total space needed.  You can dispense
 * with these routines if you have plenty of virtual memory; see jmemnobs.c.
 */


METHODDEF void
    read_backing_store(backing_store_ptr info, void FAR * buffer_address,
                           long file_offset, long byte_count)
{
   if (fseek(info->temp_file, file_offset, SEEK_SET))
      ERREXIT(methods, "fseek failed on temporary file");
   if (JFREAD(info->temp_file, buffer_address, byte_count)
       != (size_t) byte_count)
      ERREXIT(methods, "fread failed on temporary file");
}


METHODDEF void
    write_backing_store(backing_store_ptr info, void FAR * buffer_address,
                            long file_offset, long byte_count)
{
   if (fseek(info->temp_file, file_offset, SEEK_SET))
      ERREXIT(methods, "fseek failed on temporary file");
   if (JFWRITE(info->temp_file, buffer_address, byte_count)
       != (size_t) byte_count)
      ERREXIT(methods, "fwrite failed on temporary file --- out of disk space?");
}


METHODDEF void
    close_backing_store(backing_store_ptr info)
{
   fclose(info->temp_file);
   /*
      Since this implementation uses tmpfile() to create the file, no
      explicit file deletion is needed.
   */
}


/*
 * Initial opening of a backing-store object.
 *
 * This version uses tmpfile(), which constructs a suitable file name
 * behind the scenes.  We don't have to use temp_name[] at all;
 * indeed, we can't even find out the actual name of the temp file.
 */

GLOBAL void
    jopen_backing_store(backing_store_ptr info, long total_bytes_needed)
{
   if ((info->temp_file = tmpfile()) == NULL)
      ERREXIT(methods, "Failed to create temporary file");
   info->read_backing_store = read_backing_store;
   info->write_backing_store = write_backing_store;
   info->close_backing_store = close_backing_store;
}


/*
 * These routines take care of any system-dependent initialization and
 * cleanup required.  Keep in mind that jmem_term may be called more than
 * once.
 */

GLOBAL void
    jmem_init(external_methods_ptr emethods)
{
   methods = emethods;          /* save struct addr for error exit access */
   emethods->max_memory_to_use = FYEO_mem_available();
}

GLOBAL void
    jmem_term(void)
{
   FYEO_mem_term();
}
