vx32

jmemmgr.c (40988B)

---

 /*
  * jmemmgr.c
  *
  * Copyright (C) 1991-1997, 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 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(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.
  */
 
 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) {
 	jzero_far((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;
 
       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 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);
 }
 
 
 /*
  * 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->hdr.next;
     space_freed = lhdr_ptr->hdr.bytes_used +
 		  lhdr_ptr->hdr.bytes_left +
 		  SIZEOF(large_pool_hdr);
     jpeg_free_large(cinfo, (void FAR *) 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->hdr.next;
     space_freed = shdr_ptr->hdr.bytes_used +
 		  shdr_ptr->hdr.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 ((SIZEOF(ALIGN_TYPE) & (SIZEOF(ALIGN_TYPE)-1)) != 0)
     ERREXIT(cinfo, JERR_BAD_ALIGN_TYPE);
   /* MAX_ALLOC_CHUNK must be representable as type size_t, and must be
    * a multiple of SIZEOF(ALIGN_TYPE).
    * 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 % SIZEOF(ALIGN_TYPE)) != 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
 
 }