/*
 * jmemmgr.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2016, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * 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(const char *name);

#endif
#endif


LOCAL(size_t)
round_up_pow2(size_t a, size_t b)
/* a rounded up to the next multiple of b, i.e. ceil(a/b)*b */
/* Assumes a >= 0, b > 0, and b is a power of 2 */
{
	return ((a + b - 1) & (~(b - 1)));
}


/*
 * 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 ALIGN_SIZE.
 * By default, we define ALIGN_SIZE as sizeof(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_SIZE 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_SIZE 4" in jconfig.h if you have
 * such a compiler.
 */

#ifndef ALIGN_SIZE              /* so can override from jconfig.h */
#ifndef WITH_SIMD
#define ALIGN_SIZE  sizeof(double)
#else
#define ALIGN_SIZE  16 /* Most SIMD implementations require this */
#endif
#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.
 */

typedef struct small_pool_struct *small_pool_ptr;

typedef struct small_pool_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 */
} small_pool_hdr;

typedef struct large_pool_struct *large_pool_ptr;

typedef struct large_pool_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 */
} 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 */
	size_t 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->next) {
	fprintf(stderr, "  Large chunk used %ld\n",
			(long) lhdr_ptr->bytes_used);
  }

  for (shdr_ptr = mem->small_list[pool_id]; shdr_ptr != NULL;
	   shdr_ptr = shdr_ptr->next) {
	fprintf(stderr, "  Small chunk used %ld free %ld\n",
			(long) shdr_ptr->bytes_used,
			(long) shdr_ptr->bytes_left);
  }
}

#endif /* MEM_STATS */


LOCAL(void)
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.
 *
 * Since we do not know what alignment malloc() gives us, we have to
 * allocate ALIGN_SIZE-1 extra space per pool to have room for alignment
 * adjustment.
 */

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 min_request, slop;

	/*
	 * Round up the requested size to a multiple of ALIGN_SIZE in order
	 * to assure alignment for the next object allocated in the same pool
	 * and so that algorithms can straddle outside the proper area up
	 * to the next alignment.
	 */
	if (sizeofobject > MAX_ALLOC_CHUNK) {
		/* This prevents overflow/wrap-around in round_up_pow2() if sizeofobject
		   is close to SIZE_MAX. */
		out_of_memory(cinfo, 7);
	}
	sizeofobject = round_up_pow2(sizeofobject, ALIGN_SIZE);

	/* Check for unsatisfiable request (do now to ensure no overflow below) */
	if ((sizeof(small_pool_hdr) + sizeofobject + ALIGN_SIZE - 1) >
	    MAX_ALLOC_CHUNK)
		out_of_memory(cinfo, 1);    /* request exceeds malloc's ability */

	/* 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->bytes_left >= sizeofobject)
			break;                    /* found pool with enough space */
		prev_hdr_ptr = hdr_ptr;
		hdr_ptr = hdr_ptr->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 = sizeof(small_pool_hdr) + sizeofobject + ALIGN_SIZE - 1;
		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->next = NULL;
		hdr_ptr->bytes_used = 0;
		hdr_ptr->bytes_left = sizeofobject + slop;
		if (prev_hdr_ptr == NULL)   /* first pool in class? */
			mem->small_list[pool_id] = hdr_ptr;
		else
			prev_hdr_ptr->next = hdr_ptr;
	}

	/* OK, allocate the object from the current pool */
	data_ptr = (char *) hdr_ptr; /* point to first data byte in pool... */
	data_ptr += sizeof(small_pool_hdr); /* ...by skipping the header... */
	if ((size_t) data_ptr % ALIGN_SIZE) /* ...and adjust for alignment */
		data_ptr += ALIGN_SIZE - (size_t) data_ptr % ALIGN_SIZE;
	data_ptr += hdr_ptr->bytes_used; /* point to place for object */
	hdr_ptr->bytes_used += sizeofobject;
	hdr_ptr->bytes_left -= sizeofobject;

	return (void *) data_ptr;
}


/*
 * Allocation of "large" objects.
 *
 * The external semantics of these are the same as "small" objects.  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 *)
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;
	char *data_ptr;

	/*
	 * Round up the requested size to a multiple of ALIGN_SIZE so that
	 * algorithms can straddle outside the proper area up to the next
	 * alignment.
	 */
	if (sizeofobject > MAX_ALLOC_CHUNK) {
		/* This prevents overflow/wrap-around in round_up_pow2() if sizeofobject
		   is close to SIZE_MAX. */
		out_of_memory(cinfo, 8);
	}
	sizeofobject = round_up_pow2(sizeofobject, ALIGN_SIZE);

	/* Check for unsatisfiable request (do now to ensure no overflow below) */
	if ((sizeof(large_pool_hdr) + sizeofobject + ALIGN_SIZE - 1) >
	    MAX_ALLOC_CHUNK)
		out_of_memory(cinfo, 3);    /* request exceeds malloc's ability */

	/* 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) +
	                                                 ALIGN_SIZE - 1);
	if (hdr_ptr == NULL)
		out_of_memory(cinfo, 4);    /* jpeg_get_large failed */
	mem->total_space_allocated += sizeofobject + sizeof(large_pool_hdr) +
	                              ALIGN_SIZE - 1;

	/* Success, initialize the new pool header and add to list */
	hdr_ptr->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->bytes_used = sizeofobject;
	hdr_ptr->bytes_left = 0;
	mem->large_list[pool_id] = hdr_ptr;

	data_ptr = (char *) hdr_ptr; /* point to first data byte in pool... */
	data_ptr += sizeof(small_pool_hdr); /* ...by skipping the header... */
	if ((size_t) data_ptr % ALIGN_SIZE) /* ...and adjust for alignment */
		data_ptr += ALIGN_SIZE - (size_t) data_ptr % ALIGN_SIZE;

	return (void *) data_ptr;
}


/*
 * Creation of 2-D sample arrays.
 *
 * 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.
 *
 * Since we are often upsampling with a factor 2, we align the size (not
 * the start) to 2 * ALIGN_SIZE so that the upsampling routines don't have
 * to be as careful about size.
 */

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;

	/* Make sure each row is properly aligned */
	if ((ALIGN_SIZE % sizeof(JSAMPLE)) != 0)
		out_of_memory(cinfo, 5);    /* safety check */

	if (samplesperrow > MAX_ALLOC_CHUNK) {
		/* This prevents overflow/wrap-around in round_up_pow2() if sizeofobject
		   is close to SIZE_MAX. */
		out_of_memory(cinfo, 9);
	}
	samplesperrow = (JDIMENSION) round_up_pow2(samplesperrow, (2 * ALIGN_SIZE) /
	                                                          sizeof(JSAMPLE));

	/* 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;

	/* Make sure each row is properly aligned */
	if ((sizeof(JBLOCK) % ALIGN_SIZE) != 0)
		out_of_memory(cinfo, 6);    /* safety check */

	/* 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;
	size_t space_per_minheight, maximum_space, avail_mem;
	size_t 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 *) ptr->mem_buffer[i],
			                                     file_offset, byte_count);
		else
			(*ptr->b_s_info.read_backing_store)(cinfo, &ptr->b_s_info,
			                                    (void *) 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 *) ptr->mem_buffer[i],
			                                     file_offset, byte_count);
		else
			(*ptr->b_s_info.read_backing_store)(cinfo, &ptr->b_s_info,
			                                    (void *) 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) {
				jzero_far((void *) 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;

			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_barray_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->blocksperrow * sizeof(JBLOCK);
			undef_row -= ptr->cur_start_row; /* make indexes relative to buffer */
			end_row -= ptr->cur_start_row;
			while (undef_row < end_row) {
				jzero_far((void *) 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);
}


/*
 * Release all objects belonging to a specified pool.
 */

METHODDEF(void)
free_pool(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;
	size_t space_freed;

	if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
		ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id); /* safety check */

#ifdef MEM_STATS
	if (cinfo->err->trace_level > 1)
	  print_mem_stats(cinfo, pool_id); /* print pool's memory usage statistics */
#endif

	/* If freeing IMAGE pool, close any virtual arrays first */
	if (pool_id == JPOOL_IMAGE) {
		jvirt_sarray_ptr sptr;
		jvirt_barray_ptr bptr;

		for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
			if (sptr->b_s_open) {     /* there may be no backing store */
				sptr->b_s_open = FALSE; /* prevent recursive close if error */
				(*sptr->b_s_info.close_backing_store)(cinfo, &sptr->b_s_info);
			}
		}
		mem->virt_sarray_list = NULL;
		for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
			if (bptr->b_s_open) {     /* there may be no backing store */
				bptr->b_s_open = FALSE; /* prevent recursive close if error */
				(*bptr->b_s_info.close_backing_store)(cinfo, &bptr->b_s_info);
			}
		}
		mem->virt_barray_list = NULL;
	}

	/* Release large objects */
	lhdr_ptr = mem->large_list[pool_id];
	mem->large_list[pool_id] = NULL;

	while (lhdr_ptr != NULL) {
		large_pool_ptr next_lhdr_ptr = lhdr_ptr->next;
		space_freed = lhdr_ptr->bytes_used +
		              lhdr_ptr->bytes_left +
		              sizeof(large_pool_hdr);
		jpeg_free_large(cinfo, (void *) lhdr_ptr, space_freed);
		mem->total_space_allocated -= space_freed;
		lhdr_ptr = next_lhdr_ptr;
	}

	/* Release small objects */
	shdr_ptr = mem->small_list[pool_id];
	mem->small_list[pool_id] = NULL;

	while (shdr_ptr != NULL) {
		small_pool_ptr next_shdr_ptr = shdr_ptr->next;
		space_freed = shdr_ptr->bytes_used +
		              shdr_ptr->bytes_left +
		              sizeof(small_pool_hdr);
		jpeg_free_small(cinfo, (void *) shdr_ptr, space_freed);
		mem->total_space_allocated -= space_freed;
		shdr_ptr = next_shdr_ptr;
	}
}


/*
 * Close up shop entirely.
 * Note that this cannot be called unless cinfo->mem is non-NULL.
 */

METHODDEF(void)
self_destruct(j_common_ptr cinfo) {
	int pool;

	/* Close all backing store, release all memory.
	 * Releasing pools in reverse order might help avoid fragmentation
	 * with some (brain-damaged) malloc libraries.
	 */
	for (pool = JPOOL_NUMPOOLS - 1; pool >= JPOOL_PERMANENT; pool--) {
		free_pool(cinfo, pool);
	}

	/* Release the memory manager control block too. */
	jpeg_free_small(cinfo, (void *) cinfo->mem, sizeof(my_memory_mgr));
	cinfo->mem = NULL;            /* ensures I will be called only once */

	jpeg_mem_term(cinfo);         /* system-dependent cleanup */
}


/*
 * Memory manager initialization.
 * When this is called, only the error manager pointer is valid in cinfo!
 */

GLOBAL(void)
jinit_memory_mgr(j_common_ptr cinfo) {
	my_mem_ptr mem;
	long max_to_use;
	int pool;
	size_t test_mac;

	cinfo->mem = NULL;            /* for safety if init fails */

	/* Check for configuration errors.
	 * sizeof(ALIGN_TYPE) should be a power of 2; otherwise, it probably
	 * doesn't reflect any real hardware alignment requirement.
	 * The test is a little tricky: for X>0, X and X-1 have no one-bits
	 * in common if and only if X is a power of 2, ie has only one one-bit.
	 * Some compilers may give an "unreachable code" warning here; ignore it.
	 */
	if ((ALIGN_SIZE & (ALIGN_SIZE - 1)) != 0)
		ERREXIT(cinfo, JERR_BAD_ALIGN_TYPE);
	/* MAX_ALLOC_CHUNK must be representable as type size_t, and must be
	 * a multiple of ALIGN_SIZE.
	 * Again, an "unreachable code" warning may be ignored here.
	 * But a "constant too large" warning means you need to fix MAX_ALLOC_CHUNK.
	 */
	test_mac = (size_t) MAX_ALLOC_CHUNK;
	if ((long) test_mac != MAX_ALLOC_CHUNK ||
	    (MAX_ALLOC_CHUNK % ALIGN_SIZE) != 0)
		ERREXIT(cinfo, JERR_BAD_ALLOC_CHUNK);

	max_to_use = jpeg_mem_init(cinfo); /* system-dependent initialization */

	/* Attempt to allocate memory manager's control block */
	mem = (my_mem_ptr) jpeg_get_small(cinfo, sizeof(my_memory_mgr));

	if (mem == NULL) {
		jpeg_mem_term(cinfo);       /* system-dependent cleanup */
		ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, 0);
	}

	/* OK, fill in the method pointers */
	mem->pub.alloc_small = alloc_small;
	mem->pub.alloc_large = alloc_large;
	mem->pub.alloc_sarray = alloc_sarray;
	mem->pub.alloc_barray = alloc_barray;
	mem->pub.request_virt_sarray = request_virt_sarray;
	mem->pub.request_virt_barray = request_virt_barray;
	mem->pub.realize_virt_arrays = realize_virt_arrays;
	mem->pub.access_virt_sarray = access_virt_sarray;
	mem->pub.access_virt_barray = access_virt_barray;
	mem->pub.free_pool = free_pool;
	mem->pub.self_destruct = self_destruct;

	/* Make MAX_ALLOC_CHUNK accessible to other modules */
	mem->pub.max_alloc_chunk = MAX_ALLOC_CHUNK;

	/* Initialize working state */
	mem->pub.max_memory_to_use = max_to_use;

	for (pool = JPOOL_NUMPOOLS - 1; pool >= JPOOL_PERMANENT; pool--) {
		mem->small_list[pool] = NULL;
		mem->large_list[pool] = NULL;
	}
	mem->virt_sarray_list = NULL;
	mem->virt_barray_list = NULL;

	mem->total_space_allocated = sizeof(my_memory_mgr);

	/* Declare ourselves open for business */
	cinfo->mem = &mem->pub;

	/* Check for an environment variable JPEGMEM; if found, override the
	 * default max_memory setting from jpeg_mem_init.  Note that the
	 * surrounding application may again override this value.
	 * If your system doesn't support getenv(), define NO_GETENV to disable
	 * this feature.
	 */
#ifndef NO_GETENV
	{
		char *memenv;

		if ((memenv = getenv("JPEGMEM")) != NULL) {
			char ch = 'x';

			if (sscanf(memenv, "%ld%c", &max_to_use, &ch) > 0) {
				if (ch == 'm' || ch == 'M')
					max_to_use *= 1000L;
				mem->pub.max_memory_to_use = max_to_use * 1000L;
			}
		}
	}
#endif

}
