JPEGView/Independent JPEG Group/jmemmgr.c

/*
 * jmemmgr.c
 *
 * Copyright (C) 1991-1994, 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 contains the JPEG system-independent memory management
 * routines.  This code is usable across a wide variety of machines; most
 * of the system dependencies have been isolated in a separate file.
 * The major functions provided here are:
 *   * pool-based allocation and freeing of memory;
 *   * policy decisions about how to divide available memory among the
 *     virtual arrays;
 *   * control logic for swapping virtual arrays between main memory and
 *     backing storage.
 * The separate system-dependent file provides the actual backing-storage
 * access code, and it contains the policy decision about how much total
 * main memory to use.
 * This file is system-dependent in the sense that some of its functions
 * are unnecessary in some systems.  For example, if there is enough virtual
 * memory so that backing storage will never be used, much of the virtual
 * array control logic could be removed.  (Of course, if you have that much
 * memory then you shouldn't care about a little bit of unused code...)
 */

#define JPEG_INTERNALS
#define AM_MEMORY_MANAGER	/* we define jvirt_Xarray_control structs */
#include "jinclude.h"
#include "jpeglib.h"
#include "jmemsys.h"		/* import the system-dependent declarations */

#ifndef NO_GETENV
#ifndef HAVE_STDLIB_H		/* <stdlib.h> should declare getenv() */
extern char * getenv JPP((const char * name));
#endif
#endif


/*
 * Some important notes:
 *   The allocation routines provided here must never return NULL.
 *   They should exit to error_exit if unsuccessful.
 *
 *   It's not a good idea to try to merge the sarray and barray routines,
 *   even though they are textually almost the same, because samples are
 *   usually stored as bytes while coefficients are shorts or ints.  Thus,
 *   in machines where byte pointers have a different representation from
 *   word pointers, the resulting machine code could not be the same.
 */


/*
 * Many machines require storage alignment: longs must start on 4-byte
 * boundaries, doubles on 8-byte boundaries, etc.  On such machines, malloc()
 * always returns pointers that are multiples of the worst-case alignment
 * requirement, and we had better do so too.
 * There isn't any really portable way to determine the worst-case alignment
 * requirement.  This code assumes that the alignment requirement is
 * multiples of SIZEOF(align_type).  Here we define align_type as double;
 * with this definition, the code will run on all machines known to me.
 * If your machine has lesser alignment needs, you can save a few bytes
 * by making align_type smaller.
 */

typedef double align_type;


/*
 * We allocate objects from "pools", where each pool is gotten with a single
 * request to jpeg_get_small() or jpeg_get_large().  There is no per-object
 * overhead within a pool, except for alignment padding.  Each pool has a
 * header with a link to the next pool of the same class.
 * Small and large pool headers are identical except that the latter's
 * link pointer must be FAR on 80x86 machines.
 * Notice that the "real" header fields are union'ed with a dummy align_type
 * field.  This forces the compiler to make SIZEOF(small_pool_hdr) a multiple
 * of the alignment requirement of align_type.
 */

typedef union small_pool_struct * small_pool_ptr;

typedef union small_pool_struct {
  struct {
    small_pool_ptr next;	/* next in list of pools */
    size_t bytes_used;		/* how many bytes already used within pool */
    size_t bytes_left;		/* bytes still available in this pool */
  } hdr;
  align_type dummy;		/* included in union to ensure alignment */
} small_pool_hdr;

typedef union large_pool_struct FAR * large_pool_ptr;

typedef union large_pool_struct {
  struct {
    large_pool_ptr next;	/* next in list of pools */
    size_t bytes_used;		/* how many bytes already used within pool */
    size_t bytes_left;		/* bytes still available in this