/*

 * jmemmgr.c

 *

 * Copyright (C) 1991-1997, Thomas G. Lane.

 * Modified 2011-2012 by Guido Vollbeding.

 * 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() */</stdlib.h>

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 module assumes that the alignment requirement is

 * multiples of sizeof(ALIGN_TYPE).

 * By default, we define ALIGN_TYPE as double.  This is necessary on some

 * workstations (where doubles really do need 8-byte alignment) and will work

 * fine on nearly everything.  If your machine has lesser alignment needs,

 * you can save a few bytes by making ALIGN_TYPE smaller.

 * The only place I know of where this will NOT work is certain Macintosh

 * 680x0 compilers that define double as a 10-byte IEEE extended float.

 * Doing 10-byte alignment is counterproductive because longwords won't be

 * aligned well.  Put "#define ALIGN_TYPE long" in jconfig.h if you have

 * such a compiler.

 */

#ifndef ALIGN_TYPE		/* so can override from jconfig.h */

#define ALIGN_TYPE  double

#endif

/*

 * 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 pool */

  } hdr;

  ALIGN_TYPE dummy;		/* included in union to ensure alignment */

} large_pool_hdr;

/*

 * Here is the full definition of a memory manager object.

 */

typedef struct {

  struct jpeg_memory_mgr pub;	/* public fields */

  /* Each pool identifier (lifetime class) names a linked list of pools. */

  small_pool_ptr small_list[JPOOL_NUMPOOLS];

  large_pool_ptr large_list[JPOOL_NUMPOOLS];

  /* Since we only have one lifetime class of virtual arrays, only one

   * linked list is necessary (for each datatype).  Note that the virtual

   * array control blocks being linked together are actually stored somewhere

   * in the small-pool list.

   */

  jvirt_sarray_ptr virt_sarray_list;

  jvirt_barray_ptr virt_barray_list;

  /* This counts total space obtained from jpeg_get_small/large */

  long total_space_allocated;

  /* alloc_sarray and alloc_barray set this value for use by virtual

   * array routines.

   */

  JDIMENSION last_rowsperchunk;	/* from most recent alloc_sarray/barray */

} my_memory_mgr;

typedef my_memory_mgr * my_mem_ptr;

/*

 * The control blocks for virtual arrays.

 * Note that these blocks are allocated in the "small" pool area.

 * System-dependent info for the associated backing store (if any) is hidden

 * inside the backing_store_info struct.

 */

struct jvirt_sarray_control {

  JSAMPARRAY mem_buffer;	/* => the in-memory buffer */

  JDIMENSION rows_in_array;	/* total virtual array height */

  JDIMENSION samplesperrow;	/* width of array (and of memory buffer) */

  JDIMENSION maxaccess;		/* max rows accessed by access_virt_sarray */

  JDIMENSION rows_in_mem;	/* height of memory buffer */

  JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */

  JDIMENSION cur_start_row;	/* first logical row # in the buffer */

  JDIMENSION first_undef_row;	/* row # of first uninitialized row */

  boolean pre_zero;		/* pre-zero mode requested? */

  boolean dirty;		/* do current buffer contents need written? */

  boolean b_s_open;		/* is backing-store data valid? */

  jvirt_sarray_ptr next;	/* link to next virtual sarray control block */

  backing_store_info b_s_info;	/* System-dependent control info */

};

struct jvirt_barray_control {

  JBLOCKARRAY mem_buffer;	/* => the in-memory buffer */

  JDIMENSION rows_in_array;	/* total virtual array height */

  JDIMENSION blocksperrow;	/* width of array (and of memory buffer) */

  JDIMENSION maxaccess;		/* max rows accessed by access_virt_barray */

  JDIMENSION rows_in_mem;	/* height of memory buffer */

  JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */

  JDIMENSION cur_start_row;	/* first logical row # in the buffer */

  JDIMENSION first_undef_row;	/* row # of first uninitialized row */

  boolean pre_zero;		/* pre-zero mode requested? */

  boolean dirty;		/* do current buffer contents need written? */

  boolean b_s_open;		/* is backing-store data valid? */

  jvirt_barray_ptr next;	/* link to next virtual barray control block */

  backing_store_info b_s_info;	/* System-dependent control info */

};

#ifdef MEM_STATS		/* optional extra stuff for statistics */

LOCAL(void)

print_mem_stats (j_common_ptr cinfo, int pool_id)

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  small_pool_ptr shdr_ptr;

  large_pool_ptr lhdr_ptr;

  /* Since this is only a debugging stub, we can cheat a little by using

   * fprintf directly rather than going through the trace message code.

   * This is helpful because message parm array can't handle longs.

   */

  fprintf(stderr, "Freeing pool %d, total space = %ld\n",

	  pool_id, mem->total_space_allocated);

  for (lhdr_ptr = mem->large_list[pool_id]; lhdr_ptr != NULL;

       lhdr_ptr = lhdr_ptr->hdr.next) {

    fprintf(stderr, "  Large chunk used %ld\n",

	    (long) lhdr_ptr->hdr.bytes_used);

  }

  for (shdr_ptr = mem->small_list[pool_id]; shdr_ptr != NULL;

       shdr_ptr = shdr_ptr->hdr.next) {

    fprintf(stderr, "  Small chunk used %ld free %ld\n",

	    (long) shdr_ptr->hdr.bytes_used,

	    (long) shdr_ptr->hdr.bytes_left);

  }

}

#endif /* MEM_STATS */

LOCAL(noreturn_t)

out_of_memory (j_common_ptr cinfo, int which)

/* Report an out-of-memory error and stop execution */

/* If we compiled MEM_STATS support, report alloc requests before dying */

{

#ifdef MEM_STATS

  cinfo->err->trace_level = 2;	/* force self_destruct to report stats */

#endif

  ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, which);

}

/*

 * Allocation of "small" objects.

 *

 * For these, we use pooled storage.  When a new pool must be created,

 * we try to get enough space for the current request plus a "slop" factor,

 * where the slop will be the amount of leftover space in the new pool.

 * The speed vs. space tradeoff is largely determined by the slop values.

 * A different slop value is provided for each pool class (lifetime),

 * and we also distinguish the first pool of a class from later ones.

 * NOTE: the values given work fairly well on both 16- and 32-bit-int

 * machines, but may be too small if longs are 64 bits or more.

 */

static const size_t first_pool_slop[JPOOL_NUMPOOLS] = 

{

	1600,			/* first PERMANENT pool */

	16000			/* first IMAGE pool */

};

static const size_t extra_pool_slop[JPOOL_NUMPOOLS] = 

{

	0,			/* additional PERMANENT pools */

	5000			/* additional IMAGE pools */

};

#define MIN_SLOP  50		/* greater than 0 to avoid futile looping */

METHODDEF(void *)

alloc_small (j_common_ptr cinfo, int pool_id, size_t sizeofobject)

/* Allocate a "small" object */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  small_pool_ptr hdr_ptr, prev_hdr_ptr;

  char * data_ptr;

  size_t odd_bytes, min_request, slop;

  /* Check for unsatisfiable request (do now to ensure no overflow below) */

  if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(small_pool_hdr)))

    out_of_memory(cinfo, 1);	/* request exceeds malloc's ability */

  /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */

  odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);

  if (odd_bytes > 0)

    sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;

  /* See if space is available in any existing pool */

  if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)

    ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

  prev_hdr_ptr = NULL;

  hdr_ptr = mem->small_list[pool_id];

  while (hdr_ptr != NULL) {

    if (hdr_ptr->hdr.bytes_left >= sizeofobject)

      break;			/* found pool with enough space */

    prev_hdr_ptr = hdr_ptr;

    hdr_ptr = hdr_ptr->hdr.next;

  }

  /* Time to make a new pool? */

  if (hdr_ptr == NULL) {

    /* min_request is what we need now, slop is what will be leftover */

    min_request = sizeofobject + SIZEOF(small_pool_hdr);

    if (prev_hdr_ptr == NULL)	/* first pool in class? */

      slop = first_pool_slop[pool_id];

    else

      slop = extra_pool_slop[pool_id];

    /* Don't ask for more than MAX_ALLOC_CHUNK */

    if (slop > (size_t) (MAX_ALLOC_CHUNK-min_request))

      slop = (size_t) (MAX_ALLOC_CHUNK-min_request);

    /* Try to get space, if fail reduce slop and try again */

    for (;;) {

      hdr_ptr = (small_pool_ptr) jpeg_get_small(cinfo, min_request + slop);

      if (hdr_ptr != NULL)

	break;

      slop /= 2;

      if (slop < MIN_SLOP)	/* give up when it gets real small */

	out_of_memory(cinfo, 2); /* jpeg_get_small failed */

    }

    mem->total_space_allocated += min_request + slop;

    /* Success, initialize the new pool header and add to end of list */

    hdr_ptr->hdr.next = NULL;

    hdr_ptr->hdr.bytes_used = 0;

    hdr_ptr->hdr.bytes_left = sizeofobject + slop;

    if (prev_hdr_ptr == NULL)	/* first pool in class? */

      mem->small_list[pool_id] = hdr_ptr;

    else

      prev_hdr_ptr->hdr.next = hdr_ptr;

  }

  /* OK, allocate the object from the current pool */

  data_ptr = (char *) (hdr_ptr + 1); /* point to first data byte in pool */

  data_ptr += hdr_ptr->hdr.bytes_used; /* point to place for object */

  hdr_ptr->hdr.bytes_used += sizeofobject;

  hdr_ptr->hdr.bytes_left -= sizeofobject;

  return (void *) data_ptr;

}

/*

 * Allocation of "large" objects.

 *

 * The external semantics of these are the same as "small" objects,

 * except that FAR pointers are used on 80x86.  However the pool

 * management heuristics are quite different.  We assume that each

 * request is large enough that it may as well be passed directly to

 * jpeg_get_large; the pool management just links everything together

 * so that we can free it all on demand.

 * Note: the major use of "large" objects is in JSAMPARRAY and JBLOCKARRAY

 * structures.  The routines that create these structures (see below)

 * deliberately bunch rows together to ensure a large request size.

 */

METHODDEF(void FAR *)

alloc_large (j_common_ptr cinfo, int pool_id, size_t sizeofobject)

/* Allocate a "large" object */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  large_pool_ptr hdr_ptr;

  size_t odd_bytes;

  /* Check for unsatisfiable request (do now to ensure no overflow below) */

  if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)))

    out_of_memory(cinfo, 3);	/* request exceeds malloc's ability */

  /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */

  odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);

  if (odd_bytes > 0)

    sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;

  /* Always make a new pool */

  if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)

    ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

  hdr_ptr = (large_pool_ptr) jpeg_get_large(cinfo, sizeofobject +

					    SIZEOF(large_pool_hdr));

  if (hdr_ptr == NULL)

    out_of_memory(cinfo, 4);	/* jpeg_get_large failed */

  mem->total_space_allocated += sizeofobject + SIZEOF(large_pool_hdr);

  /* Success, initialize the new pool header and add to list */

  hdr_ptr->hdr.next = mem->large_list[pool_id];

  /* We maintain space counts in each pool header for statistical purposes,

   * even though they are not needed for allocation.

   */

  hdr_ptr->hdr.bytes_used = sizeofobject;

  hdr_ptr->hdr.bytes_left = 0;

  mem->large_list[pool_id] = hdr_ptr;

  return (void FAR *) (hdr_ptr + 1); /* point to first data byte in pool */

}

/*

 * Creation of 2-D sample arrays.

 * The pointers are in near heap, the samples themselves in FAR heap.

 *

 * To minimize allocation overhead and to allow I/O of large contiguous

 * blocks, we allocate the sample rows in groups of as many rows as possible

 * without exceeding MAX_ALLOC_CHUNK total bytes per allocation request.

 * NB: the virtual array control routines, later in this file, know about

 * this chunking of rows.  The rowsperchunk value is left in the mem manager

 * object so that it can be saved away if this sarray is the workspace for

 * a virtual array.

 */

METHODDEF(JSAMPARRAY)

alloc_sarray (j_common_ptr cinfo, int pool_id,

	      JDIMENSION samplesperrow, JDIMENSION numrows)

/* Allocate a 2-D sample array */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  JSAMPARRAY result;

  JSAMPROW workspace;

  JDIMENSION rowsperchunk, currow, i;

  long ltemp;

  /* Calculate max # of rows allowed in one allocation chunk */

  ltemp = (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)) /

	  ((long) samplesperrow * SIZEOF(JSAMPLE));

  if (ltemp <= 0)

    ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);

  if (ltemp < (long) numrows)

    rowsperchunk = (JDIMENSION) ltemp;

  else

    rowsperchunk = numrows;

  mem->last_rowsperchunk = rowsperchunk;

  /* Get space for row pointers (small object) */

  result = (JSAMPARRAY) alloc_small(cinfo, pool_id,

				    (size_t) (numrows * SIZEOF(JSAMPROW)));

  /* Get the rows themselves (large objects) */

  currow = 0;

  while (currow < numrows) {

    rowsperchunk = MIN(rowsperchunk, numrows - currow);

    workspace = (JSAMPROW) alloc_large(cinfo, pool_id,

	(size_t) ((size_t) rowsperchunk * (size_t) samplesperrow

		  * SIZEOF(JSAMPLE)));

    for (i = rowsperchunk; i > 0; i--) {

      result[currow++] = workspace;

      workspace += samplesperrow;

    }

  }

  return result;

}

/*

 * Creation of 2-D coefficient-block arrays.

 * This is essentially the same as the code for sample arrays, above.

 */

METHODDEF(JBLOCKARRAY)

alloc_barray (j_common_ptr cinfo, int pool_id,

	      JDIMENSION blocksperrow, JDIMENSION numrows)

/* Allocate a 2-D coefficient-block array */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  JBLOCKARRAY result;

  JBLOCKROW workspace;

  JDIMENSION rowsperchunk, currow, i;

  long ltemp;

  /* Calculate max # of rows allowed in one allocation chunk */

  ltemp = (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)) /

	  ((long) blocksperrow * SIZEOF(JBLOCK));

  if (ltemp <= 0)

    ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);

  if (ltemp < (long) numrows)

    rowsperchunk = (JDIMENSION) ltemp;

  else

    rowsperchunk = numrows;

  mem->last_rowsperchunk = rowsperchunk;

  /* Get space for row pointers (small object) */

  result = (JBLOCKARRAY) alloc_small(cinfo, pool_id,

				     (size_t) (numrows * SIZEOF(JBLOCKROW)));

  /* Get the rows themselves (large objects) */

  currow = 0;

  while (currow < numrows) {

    rowsperchunk = MIN(rowsperchunk, numrows - currow);

    workspace = (JBLOCKROW) alloc_large(cinfo, pool_id,

	(size_t) ((size_t) rowsperchunk * (size_t) blocksperrow

		  * SIZEOF(JBLOCK)));

    for (i = rowsperchunk; i > 0; i--) {

      result[currow++] = workspace;

      workspace += blocksperrow;

    }

  }

  return result;

}

/*

 * About virtual array management:

 *

 * The above "normal" array routines are only used to allocate strip buffers

 * (as wide as the image, but just a few rows high).  Full-image-sized buffers

 * are handled as "virtual" arrays.  The array is still accessed a strip at a

 * time, but the memory manager must save the whole array for repeated

 * accesses.  The intended implementation is that there is a strip buffer in

 * memory (as high as is possible given the desired memory limit), plus a

 * backing file that holds the rest of the array.

 *

 * The request_virt_array routines are told the total size of the image and

 * the maximum number of rows that will be accessed at once.  The in-memory

 * buffer must be at least as large as the maxaccess value.

 *

 * The request routines create control blocks but not the in-memory buffers.

 * That is postponed until realize_virt_arrays is called.  At that time the

 * total amount of space needed is known (approximately, anyway), so free

 * memory can be divided up fairly.

 *

 * The access_virt_array routines are responsible for making a specific strip

 * area accessible (after reading or writing the backing file, if necessary).

 * Note that the access routines are told whether the caller intends to modify

 * the accessed strip; during a read-only pass this saves having to rewrite

 * data to disk.  The access routines are also responsible for pre-zeroing

 * any newly accessed rows, if pre-zeroing was requested.

 *

 * In current usage, the access requests are usually for nonoverlapping

 * strips; that is, successive access start_row numbers differ by exactly

 * num_rows = maxaccess.  This means we can get good performance with simple

 * buffer dump/reload logic, by making the in-memory buffer be a multiple

 * of the access height; then there will never be accesses across bufferload

 * boundaries.  The code will still work with overlapping access requests,

 * but it doesn't handle bufferload overlaps very efficiently.

 */

METHODDEF(jvirt_sarray_ptr)

request_virt_sarray (j_common_ptr cinfo, int pool_id, boolean pre_zero,

		     JDIMENSION samplesperrow, JDIMENSION numrows,

		     JDIMENSION maxaccess)

/* Request a virtual 2-D sample array */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  jvirt_sarray_ptr result;

  /* Only IMAGE-lifetime virtual arrays are currently supported */

  if (pool_id != JPOOL_IMAGE)

    ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

  /* get control block */

  result = (jvirt_sarray_ptr) alloc_small(cinfo, pool_id,

					  SIZEOF(struct jvirt_sarray_control));

  result->mem_buffer = NULL;	/* marks array not yet realized */

  result->rows_in_array = numrows;

  result->samplesperrow = samplesperrow;

  result->maxaccess = maxaccess;

  result->pre_zero = pre_zero;

  result->b_s_open = FALSE;	/* no associated backing-store object */

  result->next = mem->virt_sarray_list; /* add to list of virtual arrays */

  mem->virt_sarray_list = result;

  return result;

}

METHODDEF(jvirt_barray_ptr)

request_virt_barray (j_common_ptr cinfo, int pool_id, boolean pre_zero,

		     JDIMENSION blocksperrow, JDIMENSION numrows,

		     JDIMENSION maxaccess)

/* Request a virtual 2-D coefficient-block array */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  jvirt_barray_ptr result;

  /* Only IMAGE-lifetime virtual arrays are currently supported */

  if (pool_id != JPOOL_IMAGE)

    ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

  /* get control block */

  result = (jvirt_barray_ptr) alloc_small(cinfo, pool_id,

					  SIZEOF(struct jvirt_barray_control));

  result->mem_buffer = NULL;	/* marks array not yet realized */

  result->rows_in_array = numrows;

  result->blocksperrow = blocksperrow;

  result->maxaccess = maxaccess;

  result->pre_zero = pre_zero;

  result->b_s_open = FALSE;	/* no associated backing-store object */

  result->next = mem->virt_barray_list; /* add to list of virtual arrays */

  mem->virt_barray_list = result;

  return result;

}

METHODDEF(void)

realize_virt_arrays (j_common_ptr cinfo)

/* Allocate the in-memory buffers for any unrealized virtual arrays */

{

  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;

  long space_per_minheight, maximum_space, avail_mem;

  long minheights, max_minheights;

  jvirt_sarray_ptr sptr;

  jvirt_barray_ptr bptr;

  /* Compute the minimum space needed (maxaccess rows in each buffer)

   * and the maximum space needed (full image height in each buffer).

   * These may be of use to the system-dependent jpeg_mem_available routine.

   */

  space_per_minheight = 0;

  maximum_space = 0;

  for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {

    if (sptr->mem_buffer == NULL) { /* if not realized yet */

      space_per_minheight += (long) sptr->maxaccess *

			     (long) sptr->samplesperrow * SIZEOF(JSAMPLE);

      maximum_space += (long) sptr->rows_in_array *

		       (long) sptr->samplesperrow * SIZEOF(JSAMPLE);

    }

  }

  for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {

    if (bptr->mem_buffer == NULL) { /* if not realized yet */

      space_per_minheight += (long) bptr->maxaccess *

			     (long) bptr->blocksperrow * SIZEOF(JBLOCK);

      maximum_space += (long) bptr->rows_in_array *

		       (long) bptr->blocksperrow * SIZEOF(JBLOCK);

    }

  }

  if (space_per_minheight <= 0)

    return;			/* no unrealized arrays, no work */

  /* Determine amount of memory to actually use; this is system-dependent. */

  avail_mem = jpeg_mem_available(cinfo, space_per_minheight, maximum_space,

				 mem->total_space_allocated);

  /* If the maximum space needed is available, make all the buffers full

   * height; otherwise parcel it out with the same number of minheights

   * in each buffer.

   */

  if (avail_mem >= maximum_space)

    max_minheights = 1000000000L;

  else {

    max_minheights = avail_mem / space_per_minheight;

    /* If there doesn't seem to be enough space, try to get the minimum

     * anyway.  This allows a "stub" implementation of jpeg_mem_available().

     */

    if (max_minheights <= 0)

      max_minheights = 1;

  }

  /* Allocate the in-memory buffers and initialize backing store as needed. */

  for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {

    if (sptr->mem_buffer == NULL) { /* if not realized yet */

      minheights = ((long) sptr->rows_in_array - 1L) / sptr->maxaccess + 1L;

      if (minheights <= max_minheights) {

	/* This buffer fits in memory */

	sptr->rows_in_mem = sptr->rows_in_array;

      } else {

	/* It doesn't fit in memory, create backing store. */

	sptr->rows_in_mem = (JDIMENSION) (max_minheights * sptr->maxaccess);

	jpeg_open_backing_store(cinfo, & sptr->b_s_info,

				(long) sptr->rows_in_array *

				(long) sptr->samplesperrow *

				(long) SIZEOF(JSAMPLE));

	sptr->b_s_open = TRUE;

      }

      sptr->mem_buffer = alloc_sarray(cinfo, JPOOL_IMAGE,

				      sptr->samplesperrow, sptr->rows_in_mem);

      sptr->rowsperchunk = mem->last_rowsperchunk;

      sptr->cur_start_row = 0;

      sptr->first_undef_row = 0;

      sptr->dirty = FALSE;

    }

  }

  for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {

    if (bptr->mem_buffer == NULL) { /* if not realized yet */

      minheights = ((long) bptr->rows_in_array - 1L) / bptr->maxaccess + 1L;

      if (minheights <= max_minheights) {

	/* This buffer fits in memory */

	bptr->rows_in_mem = bptr->rows_in_array;

      } else {

	/* It doesn't fit in memory, create backing store. */

	bptr->rows_in_mem = (JDIMENSION) (max_minheights * bptr->maxaccess);

	jpeg_open_backing_store(cinfo, & bptr->b_s_info,

				(long) bptr->rows_in_array *

				(long) bptr->blocksperrow *

				(long) SIZEOF(JBLOCK));

	bptr->b_s_open = TRUE;

      }

      bptr->mem_buffer = alloc_barray(cinfo, JPOOL_IMAGE,

				      bptr->blocksperrow, bptr->rows_in_mem);

      bptr->rowsperchunk = mem->last_rowsperchunk;

      bptr->cur_start_row = 0;

      bptr->first_undef_row = 0;

      bptr->dirty = FALSE;

    }

  }

}

LOCAL(void)

do_sarray_io (j_common_ptr cinfo, jvirt_sarray_ptr ptr, boolean writing)

/* Do backing store read or write of a virtual sample array */

{

  long bytesperrow, file_offset, byte_count, rows, thisrow, i;

  bytesperrow = (long) ptr->samplesperrow * SIZEOF(JSAMPLE);

  file_offset = ptr->cur_start_row * bytesperrow;

  /* Loop to read or write each allocation chunk in mem_buffer */

  for (i = 0; i < (long) ptr->rows_in_mem; i += ptr->rowsperchunk) {

    /* One chunk, but check for short chunk at end of buffer */

    rows = MIN((long) ptr->rowsperchunk, (long) ptr->rows_in_mem - i);

    /* Transfer no more than is currently defined */

    thisrow = (long) ptr->cur_start_row + i;

    rows = MIN(rows, (long) ptr->first_undef_row - thisrow);

    /* Transfer no more than fits in file */

    rows = MIN(rows, (long) ptr->rows_in_array - thisrow);

    if (rows <= 0)		/* this chunk might be past end of file! */

      break;

    byte_count = rows * bytesperrow;

    if (writing)

      (*ptr->b_s_info.write_backing_store) (cinfo, & ptr->b_s_info,

					    (void FAR *) ptr->mem_buffer[i],

					    file_offset, byte_count);

    else

      (*ptr->b_s_info.read_backing_store) (cinfo, & ptr->b_s_info,

					   (void FAR *) ptr->mem_buffer[i],

					   file_offset, byte_count);

    file_offset += byte_count;

  }

}

LOCAL(void)

do_barray_io (j_common_ptr cinfo, jvirt_barray_ptr ptr, boolean writing)

/* Do backing store read or write of a virtual coefficient-block array */

{

  long bytesperrow, file_offset, byte_count, rows, thisrow, i;

  bytesperrow = (long) ptr->blocksperrow * SIZEOF(JBLOCK);

  file_offset = ptr->cur_start_row * bytesperrow;

  /* Loop to read or write each allocation chunk in mem_buffer */

  for (i = 0; i < (long) ptr->rows_in_mem; i += ptr->rowsperchunk) {

    /* One chunk, but check for short chunk at end of buffer */

    rows = MIN((long) ptr->rowsperchunk, (long) ptr->rows_in_mem - i);

    /* Transfer no more than is currently defined */

    thisrow = (long) ptr->cur_start_row + i;

    rows = MIN(rows, (long) ptr->first_undef_row - thisrow);

    /* Transfer no more than fits in file */

    rows = MIN(rows, (long) ptr->rows_in_array - thisrow);

    if (rows <= 0)		/* this chunk might be past end of file! */

      break;

    byte_count = rows * bytesperrow;

    if (writing)

      (*ptr->b_s_info.write_backing_store) (cinfo, & ptr->b_s_info,

					    (void FAR *) ptr->mem_buffer[i],

					    file_offset, byte_count);

    else

      (*ptr->b_s_info.read_backing_store) (cinfo, & ptr->b_s_info,

					   (void FAR *) ptr->mem_buffer[i],

					   file_offset, byte_count);

    file_offset += byte_count;

  }

}

METHODDEF(JSAMPARRAY)

access_virt_sarray (j_common_ptr cinfo, jvirt_sarray_ptr ptr,

		    JDIMENSION start_row, JDIMENSION num_rows,

		    boolean writable)

/* Access the part of a virtual sample array starting at start_row */

/* and extending for num_rows rows.  writable is true if  */

/* caller intends to modify the accessed area. */

{

  JDIMENSION end_row = start_row + num_rows;

  JDIMENSION undef_row;

  /* debugging check */

  if (end_row > ptr->rows_in_array || num_rows > ptr->maxaccess ||

      ptr->mem_buffer == NULL)

    ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);

  /* Make the desired part of the virtual array accessible */

  if (start_row < ptr->cur_start_row ||

      end_row > ptr->cur_start_row+ptr->rows_in_mem) {

    if (! ptr->b_s_open)

      ERREXIT(cinfo, JERR_VIRTUAL_BUG);

    /* Flush old buffer contents if necessary */

    if (ptr->dirty) {

      do_sarray_io(cinfo, ptr, TRUE);

      ptr->dirty = FALSE;

    }

    /* Decide what part of virtual array to access.

     * Algorithm: if target address > current window, assume forward scan,

     * load starting at target address.  If target address < current window,

     * assume backward scan, load so that target area is top of window.

     * Note that when switching from forward write to forward read, will have

     * start_row = 0, so the limiting case applies and we load from 0 anyway.

     */

    if (start_row > ptr->cur_start_row) {

      ptr->cur_start_row = start_row;

    } else {

      /* use long arithmetic here to avoid overflow & unsigned problems */

      long ltemp;

      ltemp = (long) end_row - (long) ptr->rows_in_mem;

      if (ltemp < 0)

	ltemp = 0;		/* don't fall off front end of file */

      ptr->cur_start_row = (JDIMENSION) ltemp;

    }

    /* Read in the selected part of the array.

     * During the initial write pass, we will do no actual read

     * because the selected part is all undefined.

     */

    do_sarray_io(cinfo, ptr, FALSE);

  }

  /* Ensure the accessed part of the array is defined; prezero if needed.

   * To improve locality of access, we only prezero the part of the array

   * that the caller is about to access, not the entire in-memory array.

   */

  if (ptr->first_undef_row < end_row) {

    if (ptr->first_undef_row < start_row) {

      if (writable)		/* writer skipped over a section of array */

	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);

      undef_row = start_row;	/* but reader is allowed to read ahead */

    } else {

      undef_row = ptr->first_undef_row;

    }

    if (writable)

      ptr->first_undef_row = end_row;

    if (ptr->pre_zero) {

      size_t bytesperrow = (size_t) ptr->samplesperrow * SIZEOF(JSAMPLE);

      undef_row -= ptr->cur_start_row; /* make indexes relative to buffer */

      end_row -= ptr->cur_start_row;

      while (undef_row < end_row) {

	FMEMZERO((void FAR *) ptr->mem_buffer[undef_row], bytesperrow);

	undef_row++;

      }

    } else {

      if (! writable)		/* reader looking at undefined data */

	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);

    }

  }

  /* Flag the buffer dirty if caller will write in it */

  if (writable)

    ptr->dirty = TRUE;

  /* Return address of proper part of the buffer */

  return ptr->mem_buffer + (start_row - ptr->cur_start_row);

}

METHODDEF(JBLOCKARRAY)

access_virt_barray (j_common_ptr cinfo, jvirt_barray_ptr ptr,

		    JDIMENSION start_row, JDIMENSION num_rows,

		    boolean writable)

/* Access the part of a virtual block array starting at start_row */

/* and extending for num_rows rows.  writable is true if  */

/* caller intends to modify the accessed area. */

{

  JDIMENSION end_row = start_row + num_rows;

  JDIMENSION undef_row;

  /* debugging check */

  if (end_row > ptr->rows_in_array || num_rows > ptr->maxaccess ||

      ptr->mem_buffer == NULL)

    ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);

  /* Make the desired part of the virtual array accessible */

  if (start_row < ptr->cur_start_row ||

      end_row > ptr->cur_start_row+ptr->rows_in_mem) {

    if (! ptr->b_s_open)

      ERREXIT(cinfo, JERR_VIRTUAL_BUG);

    /* Flush old buffer contents if necessary */

    if (ptr->dirty) {

      do_barray_io(cinfo, ptr, TRUE);

      ptr->dirty = FALSE;

    }

    /* Decide what part of virtual array to access.

     * Algorithm: if target address > current window, assume forward scan,

     * load starting at target address.  If target address < current window,

     * assume backward scan, load so that target area is top of window.

     * Note that when switching from forward write to forward read, will have

     * start_row = 0, so the limiting case applies and we load from 0 anyway.

     */

    if (start_row > ptr->cur_start_row) {

      ptr->cur_start_row = start_row;

    } else {

      /* use long arithmetic here to avoid overflow & unsigned problems */

      long ltemp;