path: root/gs/base/gxclmem.c

/* Copyright (C) 2001-2008 Artifex Software, Inc.
   All Rights Reserved.

   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied, modified
   or distributed except as expressly authorized under the terms of that
   license.  Refer to licensing information at http://www.artifex.com/
   or contact Artifex Software, Inc.,  7 Mt. Lassen Drive - Suite A-134,
   San Rafael, CA  94903, U.S.A., +1(415)492-9861, for further information.
*/

/* $Id$ */
/* RAM-based command list implementation */
#include "memory_.h"
#include "gx.h"
#include "gserrors.h"
#include "gxclmem.h"

/*
 * Based on: memfile.c        Version: 1.4 3/21/95 14:59:33 by Ray Johnston.
 * Copyright assigned to Aladdin Enterprises.
 */

/*****************************************************************************

   This package is more or less optimal for use by the clist routines, with
   a couple of the more likely to change "tuning" parameters given in the
   two macros below -- NEED_TO_COMPRESS and GET_NUM_RAW_BUFFERS. Usually
   the NEED_TO_COMPRESS decision will be deferred as long as possible based
   on some total system free RAM space remaining.

   The data structures are in "memfile.h", and the primary 'tuning' parameter
   is MEMFILE_DATA_SIZE. This should not be too small to keep the overhead
   ratio of the block structures to the clist data small. A value of 16384
   is probably in the ballpark.

   The concept is that a memory based "file" is created initially without
   compression, with index blocks every MEMFILE_DATA_SIZE of the file. The
   primary blocks (used by the memfile_fseek logic) for indexing into the
   file are called 'logical' (LOG_MEMFILE_BLK) and the data in stored in a
   different block called a 'physical' block (PHYS_MEMFILE_BLK). When the
   file is not yet compressed, indicated by (f->phys_curr==NULL), then there
   is one physical block for each logical block. The physical block also has
   the 'data_limit' set to NULL if the data is not compressed. Thus when a
   file is not compressed there is one physical block for each logical block.

COMPRESSION.

   When compression is triggered for a file then all of the blocks except
   the last are compressed.  Compression will result in a physical block
   that holds data for more than one logical block. Each logical block now
   points to the start of compressed data in a physical block with the
   'phys_pdata' pointer. The 'data_limit' pointer in the physical block is
   where the compression logic stopped storing data (as stream data
   compressors are allowed to do). The data for the logical block may span
   to the next physical block. Once physical blocks are compressed, they are
   chained together using the 'link' field.

   The 'f->phys_curr' points to the block being filled by compression, with
   the 'f->wt.ptr' pointing to the last byte filled in the block. These are
   used during subsequent compression when the last logical block of the
   file fills the physical block.

DECOMPRESSION.

   During reading the clist, if the logical block points to an uncompressed
   physical block, then 'memfile_get_pdata' simply sets the 'pdata' and the
   'pdata_end' pointers. If the logical block was compressed, then it may
   still be resident in a cache of decompression buffers. The number of these
   decompression buffers is not critical -- even one is enough, but having
   more may prevent decompressing blocks more than once (a cache_miss). The
   number of decompression buffers, called "raw" buffers, that are attempted
   to allocate can be changed with the GET_NUM_RAW_BUFFERS macro, but no
   error occurs if less than that number can be allocated.

   If the logical block still resides in a decompression cache buffer, then
   the 'raw_block' will identify the block. If the data for a logical block
   only exists in compressed form, then the "tail" of the list of decompression
   buffers is re-used, marking the 'raw_block' of the logical block that was
   previously associated with this data to NULL.

   Whichever raw decompression buffer is accessed is moved to the head of the
   decompression buffer list in order to keep the tail of the list as the
   "least recently used".

   There are some DEBUG global static variables used to count the number of
   cache hits "tot_cache_hits" and the number of times a logical block is
   decompressed "tot_cache_miss". Note that the actual number of cache miss
   events is 'f->log_length/MEMFILE_DATA_SIZE - tot_cache_miss' since we
   assume that every logical block must be decmpressed at least once.

   Empirical results so far indicate that if one cache raw buffer for every
   32 logical blocks, then the hit/miss ratio exceeds 99%. Of course, the
   number of raw buffers should be more than 1 if possible, and in many
   implementations (single threaded), the memory usage does not increase
   during the page output step so almost all of memory can be used for
   these raw buffers to prevent the likelihood of a cache miss.

   Of course, this is dependent on reasonably efficient clist blocking
   during writing which is dependent on the data and on the BufferSpace
   value which determines the number of clist band data buffers available.
   Empirical testing shows that the overall efficiency is best if the
   BufferSpace value is 1,000,000 (as in the original Ghostscript source).
   [Note: I expected to be able to use smaller buffer sizes for some cases,
    but this resulted in a high level of thrashing...RJJ]

LIMITATIONS.

   The most serious limitation is caused by the way 'memfile_fwrite' decides
   to free up and re-initialize a file. If memfile_fwrite is called after
   a seek to any location except the start of the file, then an error is
   issued since logic is not present to properly free up on a partial file.
   This is not a problem as used by the 'clist' logic since rewind is used
   to position to the start of a file when re-using it after an 'erasepage'.

   Since the 'clist' logic always traverses the clist using fseek's to ever
   increasing locations, no optimizations of backward seeks was implemented.
   This would be relatively easy with back chain links or bi-directional
   "X-OR" pointer information to link the logical block chain. The rewind
   function is optimal and moves directly to the start of the file.

********************************************************************************/

/*
   The need to compress should be conditional on the amount of available
   memory, but we don't have a way to communicate this to these routines.
   Instead, we simply start compressing when we've allocated more than
   COMPRESSION_THRESHOLD amount of data.  The threshold should be at
   least as large as the fixed overhead of the compressor plus the
   decompressor, plus the expected compressed size of a block that size.

   As a testing measure we have a a define TEST_BAND_LIST_COMPRESSION
   which, if set, will set the threshold to a low value so as to cause
   compression to trigger.
 */
static const int64_t COMPRESSION_THRESHOLD =
#ifdef TEST_BAND_LIST_COMPRESSION
    1024; /* Low value to force compression */
#else
    500000000;  /* 0.5 Gb for host machines */
#endif

#define NEED_TO_COMPRESS(f)\
  ((f)->ok_to_compress && (f)->total_space > COMPRESSION_THRESHOLD)

   /* FOR NOW ALLOCATE 1 raw buffer for every 32 blocks (at least 8, no more than 64)    */
#define GET_NUM_RAW_BUFFERS( f ) \
         min(64, max(f->log_length/MEMFILE_DATA_SIZE/32, 8))

#define MALLOC(f, siz, cname)\
  (void *)gs_alloc_bytes((f)->data_memory, siz, cname)
#define FREE(f, obj, cname)\
  (gs_free_object((f)->data_memory, obj, cname),\
   (f)->total_space -= sizeof(*(obj)))

/* Structure descriptor for GC */
private_st_MEMFILE();

        /* forward references */
static void memfile_free_mem(MEMFILE * f);
static int memfile_init_empty(MEMFILE * f);
static int memfile_set_memory_warning(clist_file_ptr cf, int bytes_left);
static int memfile_fclose(clist_file_ptr cf, const char *fname, bool delete);
static int memfile_get_pdata(MEMFILE * f);

/************************************************/
/*   #define DEBUG      /- force statistics -/  */
/************************************************/

#ifdef DEBUG
int64_t tot_compressed;
int64_t tot_raw;
int64_t tot_cache_miss;
int64_t tot_cache_hits;
int64_t tot_swap_out;

/*
   The following pointers are here only for helping with a dumb debugger
   that can't inspect local variables!
 */
byte *decomp_wt_ptr0, *decomp_wt_limit0;
const byte *decomp_rd_ptr0, *decomp_rd_limit0;
byte *decomp_wt_ptr1, *decomp_wt_limit1;
const byte *decomp_rd_ptr1, *decomp_rd_limit1;

#endif

/* ----------------------------- Memory Allocation --------------------- */
static void *   /* allocated memory's address, 0 if failure */
allocateWithReserve(
                MEMFILE  *f,                    /* file to allocate mem to */
                int      sizeofBlock,           /* size of block to allocate */
                int      *return_code,          /* RET 0 ok, -ve GS-style error, or +1 if OK but low memory */
                const   char     *allocName,    /* name to allocate by */
                const   char     *errorMessage  /* error message to print */
)
{
    int code = 0;       /* assume success */
    void *block = MALLOC(f, sizeofBlock, allocName);

    if (block == NULL) {
        /* Try to recover block from reserve */
        if (sizeofBlock == sizeof(LOG_MEMFILE_BLK)) {
            if (f->reserveLogBlockCount > 0) {
                block = f->reserveLogBlockChain;
                f->reserveLogBlockChain = f->reserveLogBlockChain->link;
                --f->reserveLogBlockCount;
            }
        } else if (sizeofBlock == sizeof(PHYS_MEMFILE_BLK) ||
                   sizeofBlock == sizeof(RAW_BUFFER)
                   ) {
            if (f->reservePhysBlockCount > 0) {
                block = f->reservePhysBlockChain;
                f->reservePhysBlockChain = f->reservePhysBlockChain->link;
                --f->reservePhysBlockCount;
            }
        }
        if (block != NULL)
            code = 1;   /* successful, but allocated from reserve */
    }
    if (block != NULL)
        f->total_space += sizeofBlock;
    else
        code = gs_note_error(gs_error_VMerror);
    *return_code = code;
    return block;
}

/* ---------------- Open/close/unlink ---------------- */

static int
memfile_fopen(char fname[gp_file_name_sizeof], const char *fmode,
              clist_file_ptr /*MEMFILE * */  * pf,
              gs_memory_t *mem, gs_memory_t *data_mem, bool ok_to_compress)
{
    MEMFILE *f = NULL;
    int code = 0;

    *pf = NULL;         /* in case we have an error */

    /* fname[0] == 0 if this is not reopening */
    /* memfile file names begin with a flag byte == 0xff */
    if (fname[0] == '\377' && (fmode[0] == 'r' || fmode[0] == 'a')) {
        MEMFILE *base_f = NULL;

        /* reopening an existing file. */
        code = sscanf(fname+1, "%p", &base_f);
        if (code != 1) {
            code = gs_note_error(gs_error_ioerror);
            goto finish;
        }
        /* Reopen an existing file for 'read' */
        if (base_f->is_open == false) {
            /* File is not is use, just re-use it. */
            f = base_f;
            code = 0;
            goto finish;
        } else {
            /* We need to 'clone' this memfile so that each reader instance     */
            /* will be able to maintain it's own 'state'                        */
            f = gs_alloc_struct(mem, MEMFILE, &st_MEMFILE,
                                "memfile_fopen_instance(MEMFILE)");
            if (f == NULL) {
                emprintf1(mem,
                          "memfile_open_scratch(%s): gs_alloc_struct failed\n",
                          fname);
                code = gs_note_error(gs_error_VMerror);
                goto finish;
            }
            memcpy(f, base_f, sizeof(MEMFILE));
            f->memory = mem;
            f->data_memory = data_mem;
            f->compress_state = 0;              /* Not used by reader instance */
            f->decompress_state = 0;    /* make clean for GC, or alloc'n failure */
            f->reservePhysBlockChain = NULL;
            f->reservePhysBlockCount = 0;
            f->reserveLogBlockChain = NULL;
            f->reserveLogBlockCount = 0;
            f->openlist = base_f->openlist;
            base_f->openlist = f;               /* link this one in to the base memfile */
            f->base_memfile = base_f;
            f->log_curr_pos = 0;
            f->raw_head = NULL;
            f->error_code = 0;

            if (f->log_head->phys_blk->data_limit != NULL) {
                /* The file is compressed, so we need to copy the logical block */
                /* list so that it is unique to this instance, and initialize   */
                /* the decompressor.                                            */
                LOG_MEMFILE_BLK *log_block, *new_log_block;
                int i;
                int num_log_blocks = (f->log_length + MEMFILE_DATA_SIZE - 1) / MEMFILE_DATA_SIZE;
                const stream_template *decompress_template = clist_decompressor_template();

                new_log_block = MALLOC(f, num_log_blocks * sizeof(LOG_MEMFILE_BLK), "memfile_fopen" );
                if (new_log_block == NULL) {
                    code = gs_note_error(gs_error_VMerror);
                    goto finish;
                }

                /* copy the logical blocks to the new list just allocated */
                for (log_block=f->log_head, i=0; log_block != NULL; log_block=log_block->link, i++) {
                    new_log_block[i].phys_blk = log_block->phys_blk;
                    new_log_block[i].phys_pdata = log_block->phys_pdata;
                    new_log_block[i].raw_block = NULL;
                    new_log_block[i].link = log_block->link == NULL ? NULL : new_log_block + i + 1;
                }
                f->log_head = new_log_block;

                /* NB: don't need compress_state for reading */
                f->decompress_state =
                    gs_alloc_struct(mem, stream_state, decompress_template->stype,
                                    "memfile_open_scratch(decompress_state)");
                if (f->decompress_state == 0) {
                    emprintf1(mem,
                              "memfile_open_scratch(%s): gs_alloc_struct failed\n",
                              fname);
                    code = gs_note_error(gs_error_VMerror);
                    goto finish;
                }
                clist_decompressor_init(f->decompress_state);
                f->decompress_state->memory = mem;
                if (decompress_template->set_defaults)
                    (*decompress_template->set_defaults) (f->decompress_state);
            }
            f->log_curr_blk = f->log_head;
            memfile_get_pdata(f);               /* set up the initial block */

            goto finish;
        }
    }
    fname[0] = 0;       /* no file name yet */
    f = gs_alloc_struct(mem, MEMFILE, &st_MEMFILE,
                        "memfile_open_scratch(MEMFILE)");
    if (f == NULL) {
        emprintf1(mem,
                  "memfile_open_scratch(%s): gs_alloc_struct failed\n",
                  fname);
        code = gs_note_error(gs_error_VMerror);
        goto finish;
    }
    f->memory = mem;
    f->data_memory = data_mem;
    /* init an empty file, BEFORE allocating de/compress state */
    f->compress_state = 0;      /* make clean for GC, or alloc'n failure */
    f->decompress_state = 0;
    f->openlist = NULL;
    f->base_memfile = NULL;
    f->total_space = 0;
    f->reservePhysBlockChain = NULL;
    f->reservePhysBlockCount = 0;
    f->reserveLogBlockChain = NULL;
    f->reserveLogBlockCount = 0;
    /* init an empty file           */
    if ((code = memfile_init_empty(f)) < 0)
        goto finish;
    if ((code = memfile_set_memory_warning(f, 0)) < 0)
        goto finish;
    /*
     * Disregard the ok_to_compress flag, since the size threshold gives us
     * a much better criterion for deciding when compression is appropriate.
     */
    f->ok_to_compress = /*ok_to_compress */ true;
    f->compress_state = 0;      /* make clean for GC */
    f->decompress_state = 0;
    if (f->ok_to_compress) {
        const stream_template *compress_template = clist_compressor_template();
        const stream_template *decompress_template = clist_decompressor_template();

        f->compress_state =
            gs_alloc_struct(mem, stream_state, compress_template->stype,
                            "memfile_open_scratch(compress_state)");
        f->decompress_state =
            gs_alloc_struct(mem, stream_state, decompress_template->stype,
                            "memfile_open_scratch(decompress_state)");
        if (f->compress_state == 0 || f->decompress_state == 0) {
            emprintf1(mem,
                      "memfile_open_scratch(%s): gs_alloc_struct failed\n",
                      fname);
            code = gs_note_error(gs_error_VMerror);
            goto finish;
        }
        clist_compressor_init(f->compress_state);
        clist_decompressor_init(f->decompress_state);
        f->compress_state->memory = mem;
        f->decompress_state->memory = mem;
        if (compress_template->set_defaults)
            (*compress_template->set_defaults) (f->compress_state);
        if (decompress_template->set_defaults)
            (*decompress_template->set_defaults) (f->decompress_state);
    }
    f->total_space = 0;

    /* Return the address of this memfile as a string for use in future clist_fopen calls */
    fname[0] = 0xff;        /* a flag that this is a memfile name */
    sprintf(fname+1, "%p", f);

#ifdef DEBUG
        tot_compressed = 0;
        tot_raw = 0;
        tot_cache_miss = 0;
        tot_cache_hits = 0;
        tot_swap_out = 0;
#endif

finish:
    /* 'f' shouldn't be NULL unless code < 0, but be careful */
    if (code < 0 || f == NULL) {
        /* return failure, clean up memory before leaving */
        if (f != NULL)
            memfile_fclose((clist_file_ptr)f, fname, true);
        if (code >= 0)
            code = gs_error_ioerror;
    } else {
        /* return success */
        f->is_open = true;
        *pf = f;
    }
    return code;
}

static int
memfile_fclose(clist_file_ptr cf, const char *fname, bool delete)
{
    MEMFILE *const f = (MEMFILE *)cf;

    f->is_open = false;
    if (!delete) {
        if (f->base_memfile) {
            MEMFILE *prev_f;

            /* Here we need to delete this instance from the 'openlist' */
            /* in case this file was opened for 'read' on a previously  */
            /* written file (base_memfile != NULL)                          */
            for (prev_f = f->base_memfile; prev_f != NULL; prev_f = prev_f->openlist)
                if (prev_f->openlist == f)
                    break;
            if (prev_f == NULL) {
                emprintf1(f->memory,
                          "Could not find %p on memfile openlist\n",
                          f);
                return_error(gs_error_invalidfileaccess);
            }
            prev_f->openlist = f->openlist;     /* link around the one being fclosed */
            /* Now delete this MEMFILE reader instance */
            /* NB: we don't delete 'base' instances until we delete */
            /* If the file is compressed, free the logical blocks, but not */
            /* the phys_blk info (that is still used by the base memfile   */
            if (f->log_head->phys_blk->data_limit != NULL) {
                LOG_MEMFILE_BLK *tmpbp, *bp = f->log_head;

                while (bp != NULL) {
                    tmpbp = bp->link;
                    FREE(f, bp, "memfile_free_mem(log_blk)");
                    bp = tmpbp;
                }
                f->log_head = NULL;

                /* Free any internal compressor state. */
                if (f->compressor_initialized) {
                    if (f->decompress_state->templat->release != 0)
                        (*f->decompress_state->templat->release) (f->decompress_state);
                    if (f->compress_state->templat->release != 0)
                        (*f->compress_state->templat->release) (f->compress_state);
                    f->compressor_initialized = false;
                }
                /* free the raw buffers                                           */
                while (f->raw_head != NULL) {
                    RAW_BUFFER *tmpraw = f->raw_head->fwd;

                    FREE(f, f->raw_head, "memfile_free_mem(raw)");
                    f->raw_head = tmpraw;
                }
            }
            /* deallocate the memfile object proper */
            gs_free_object(f->memory, f, "memfile_close_and_unlink(MEMFILE)");
        }
        return 0;
    }

    /* TODO: If there are open read memfile structures, set them so that  */
    /* future accesses will use the current contents. This may result in  */
    /* leaks if other users of the memfile don't 'fclose with delete=true */
    if (f->openlist != NULL || ((f->base_memfile != NULL) && f->base_memfile->is_open)) {
        /* TODO: do the cleanup rather than just giving an error */
        emprintf1(f->memory,
                  "Attempt to delete a memfile still open for read: %p\n",
                  f);
        return_error(gs_error_invalidfileaccess);
    } else {
        /* Free the memory used by this memfile */
        memfile_free_mem(f);

        /* Free reserve blocks; don't do it in memfile_free_mem because */
        /* that routine gets called to reinit file */
        while (f->reserveLogBlockChain != NULL) {
            LOG_MEMFILE_BLK *block = f->reserveLogBlockChain;

            f->reserveLogBlockChain = block->link;
            FREE(f, block, "memfile_set_block_size");
        }
        while (f->reservePhysBlockChain != NULL) {
            PHYS_MEMFILE_BLK *block = f->reservePhysBlockChain;

            f->reservePhysBlockChain = block->link;
            FREE(f, block, "memfile_set_block_size");
        }

        /* deallocate de/compress state */
        gs_free_object(f->memory, f->decompress_state,
                       "memfile_close_and_unlink(decompress_state)");
        gs_free_object(f->memory, f->compress_state,
                       "memfile_close_and_unlink(compress_state)");

        /* deallocate the memfile object proper */
        gs_free_object(f->memory, f, "memfile_close_and_unlink(MEMFILE)");
        return 0;
    }
}

static int
memfile_unlink(const char *fname)
{
    int code;
    MEMFILE *f;

    /* memfile file names begin with a flag byte == 0xff */
    if (fname[0] == '\377' && (code = sscanf(fname+1, "%p", &f) == 1)) {
        return memfile_fclose((clist_file_ptr)f, fname, true);
    } else
        return_error(gs_error_invalidfileaccess);
}

/* ---------------- Writing ---------------- */

/* Pre-alloc enough reserve mem blox to guarantee a write of N bytes will succeed */
static int      /* returns 0 ok, gs_error_VMerror if insufficient */
memfile_set_memory_warning(clist_file_ptr cf, int bytes_left)
{
    MEMFILE *const f = (MEMFILE *)cf;
    int code = 0;
    /*
     * Determine req'd memory block count from bytes_left.
     * Allocate enough phys & log blocks to hold bytes_left
     * + 1 phys blk for compress_log_blk + 1 phys blk for decompress.
     */
    int logNeeded =
        (bytes_left + MEMFILE_DATA_SIZE - 1) / MEMFILE_DATA_SIZE;
    int physNeeded = logNeeded;

    if (bytes_left > 0)
        ++physNeeded;
    if (f->raw_head == NULL)
        ++physNeeded;   /* have yet to allocate read buffers */

    /* Allocate or free memory depending on need */
    while (logNeeded > f->reserveLogBlockCount) {
        LOG_MEMFILE_BLK *block =
            MALLOC( f, sizeof(LOG_MEMFILE_BLK), "memfile_set_block_size" );

        if (block == NULL) {
            code = gs_note_error(gs_error_VMerror);
            goto finish;
        }
        block->link = f->reserveLogBlockChain;
        f->reserveLogBlockChain = block;
        ++f->reserveLogBlockCount;
    }
    while (logNeeded < f->reserveLogBlockCount) {
        LOG_MEMFILE_BLK *block = f->reserveLogBlockChain;

        f->reserveLogBlockChain = block->link;
        FREE(f, block, "memfile_set_block_size");
        --f->reserveLogBlockCount;
    }
    while (physNeeded > f->reservePhysBlockCount) {
        PHYS_MEMFILE_BLK *block =
            MALLOC( f,
                    max( sizeof(PHYS_MEMFILE_BLK), sizeof(RAW_BUFFER) ),
                    "memfile_set_block_size");

        if (block == NULL) {
            code = gs_note_error(gs_error_VMerror);
            goto finish;
        }
        block->link = f->reservePhysBlockChain;
        f->reservePhysBlockChain = block;
        ++f->reservePhysBlockCount;
    }
    while (physNeeded < f->reservePhysBlockCount) {
        PHYS_MEMFILE_BLK *block = f->reservePhysBlockChain;

        f->reservePhysBlockChain = block->link;
        FREE(f, block, "memfile_set_block_size");
        --f->reservePhysBlockCount;
    }
    f->error_code = 0;  /* memfile_set_block_size is how user resets this */
finish:
    return code;
}

static int
compress_log_blk(MEMFILE * f, LOG_MEMFILE_BLK * bp)
{
    int status;
    int ecode = 0;              /* accumulate low-memory warnings */
    int code;
    long compressed_size;
    byte *start_ptr;
    PHYS_MEMFILE_BLK *newphys;

    /* compress this block */
    f->rd.ptr = (const byte *)(bp->phys_blk->data) - 1;
    f->rd.limit = f->rd.ptr + MEMFILE_DATA_SIZE;

    bp->phys_blk = f->phys_curr;
    bp->phys_pdata = (char *)(f->wt.ptr) + 1;
    if (f->compress_state->templat->reinit != 0)
        (*f->compress_state->templat->reinit)(f->compress_state);
    compressed_size = 0;

    start_ptr = f->wt.ptr;
    status = (*f->compress_state->templat->process)(f->compress_state,
                                                    &(f->rd), &(f->wt), true);
    bp->phys_blk->data_limit = (char *)(f->wt.ptr);

    if (status == 1) {          /* More output space needed (see strimpl.h) */
        /* allocate another physical block, then compress remainder       */
        compressed_size = f->wt.limit - start_ptr;
        newphys =
            allocateWithReserve(f, sizeof(*newphys), &code, "memfile newphys",
                        "compress_log_blk : MALLOC for 'newphys' failed\n");
        if (code < 0)
            return code;
        ecode |= code;  /* accumulate any low-memory warnings */
        newphys->link = NULL;
        bp->phys_blk->link = newphys;
        f->phys_curr = newphys;
        f->wt.ptr = (byte *) (newphys->data) - 1;
        f->wt.limit = f->wt.ptr + MEMFILE_DATA_SIZE;

        start_ptr = f->wt.ptr;
        status =
            (*f->compress_state->templat->process)(f->compress_state,
                                                   &(f->rd), &(f->wt), true);
        if (status != 0) {
            /*
             * You'd think the above line is a bug, but in real life 1 src
             * block never ends up getting split across 3 dest blocks.
             */
            /* CHANGE memfile_set_memory_warning if this assumption changes. */
            emprintf(f->memory,
                     "Compression required more than one full block!\n");
            return_error(gs_error_Fatal);
        }
        newphys->data_limit = (char *)(f->wt.ptr);
    }
    compressed_size += f->wt.ptr - start_ptr;
    if (compressed_size > MEMFILE_DATA_SIZE) {
        emprintf2(f->memory,
                  "\nCompression didn't - raw=%d, compressed=%ld\n",
                  MEMFILE_DATA_SIZE,
                  compressed_size);
    }
#ifdef DEBUG
    tot_compressed += compressed_size;
#endif
    return (status < 0 ? gs_note_error(gs_error_ioerror) : ecode);
}                               /* end "compress_log_blk()"                                     */

/*      Internal (private) routine to handle end of logical block       */
static int      /* ret 0 ok, -ve error, or +ve low-memory warning */
memfile_next_blk(MEMFILE * f)
{
    LOG_MEMFILE_BLK *bp = f->log_curr_blk;
    LOG_MEMFILE_BLK *newbp;
    PHYS_MEMFILE_BLK *newphys, *oldphys;
    int ecode = 0;              /* accumulate low-memory warnings */
    int code;

    if (f->phys_curr == NULL) { /* means NOT compressing                */
        /* allocate a new block                                           */
        newphys =
            allocateWithReserve(f, sizeof(*newphys), &code, "memfile newphys",
                        "memfile_next_blk: MALLOC 1 for 'newphys' failed\n");
        if (code < 0)
            return code;
        ecode |= code;  /* accumulate low-mem warnings */
        newphys->link = NULL;
        newphys->data_limit = NULL;     /* raw                          */

        newbp =
            allocateWithReserve(f, sizeof(*newbp), &code, "memfile newbp",
                        "memfile_next_blk: MALLOC 1 for 'newbp' failed\n");
        if (code < 0) {
            FREE(f, newphys, "memfile newphys");
            return code;
        }
        ecode |= code;  /* accumulate low-mem warnings */
        bp->link = newbp;
        newbp->link = NULL;
        newbp->raw_block = NULL;
        f->log_curr_blk = newbp;

        /* check if need to start compressing                             */
        if (NEED_TO_COMPRESS(f)) {
            if_debug0(':', "[:]Beginning compression\n");
            /* compress the entire file up to this point                   */
            if (!f->compressor_initialized) {
                int code = 0;

                if (f->compress_state->templat->init != 0)
                    code = (*f->compress_state->templat->init) (f->compress_state);
                if (code < 0)
                    return_error(gs_error_VMerror);  /****** BOGUS ******/
                f->compressor_initialized = true;
            }
            /* Write into the new physical block we just allocated,        */
            /* replace it after the loop (after some blocks are freed)     */
            f->phys_curr = newphys;
            f->wt.ptr = (byte *) (newphys->data) - 1;
            f->wt.limit = f->wt.ptr + MEMFILE_DATA_SIZE;
            bp = f->log_head;
            while (bp != newbp) {       /* don't compress last block    */
                int code;

                oldphys = bp->phys_blk;
                if ((code = compress_log_blk(f, bp)) < 0)
                    return code;
                ecode |= code;
                FREE(f, oldphys, "memfile_next_blk(oldphys)");
                bp = bp->link;
            }                   /* end while( ) compress loop                           */
            /* Allocate a physical block for this (last) logical block     */
            newphys =
                allocateWithReserve(f, sizeof(*newphys), &code,
                        "memfile newphys",
                        "memfile_next_blk: MALLOC 2 for 'newphys' failed\n");
            if (code < 0)
                return code;
            ecode |= code;      /* accumulate low-mem warnings */
            newphys->link = NULL;
            newphys->data_limit = NULL;         /* raw                  */

        }                       /* end convert file to compressed                                 */
        newbp->phys_blk = newphys;
        f->pdata = newphys->data;
        f->pdata_end = newphys->data + MEMFILE_DATA_SIZE;
    }    /* end if NOT compressing                                 */
    /* File IS being compressed                                       */
    else {
        int code;

        oldphys = bp->phys_blk; /* save raw phys block ID               */
        /* compresses bp on phys list  */
        if ((code = compress_log_blk(f, bp)) < 0)
            return code;
        ecode |= code;
        newbp =
            allocateWithReserve(f, sizeof(*newbp), &code, "memfile newbp",
                        "memfile_next_blk: MALLOC 2 for 'newbp' failed\n");
        if (code < 0)
            return code;
        ecode |= code;
        bp->link = newbp;
        newbp->link = NULL;
        newbp->raw_block = NULL;
        /* Re-use the raw phys block for this new logical blk             */
        newbp->phys_blk = oldphys;
        f->pdata = oldphys->data;
        f->pdata_end = f->pdata + MEMFILE_DATA_SIZE;
        f->log_curr_blk = newbp;
    }                           /* end else (when we are compressing)                           */

    return (ecode);
}

static int      /* returns # of chars actually written */
memfile_fwrite_chars(const void *data, uint len, clist_file_ptr cf)
{
    const char *str = (const char *)data;
    MEMFILE *f = (MEMFILE *) cf;
    uint count = len;
    int ecode;

    /* check if we are writing to the start of the file.  If so, then    */
    /* free the file memory and re-initialize it (frees memory)          */
    if (f->log_curr_pos == 0) {
        int code;

        memfile_free_mem(f);
        if ((code = memfile_init_empty(f)) < 0) {
            f->error_code = code;
            return 0;
        }
    }
    if (f->log_curr_blk->link != 0) {
        emprintf(f->memory,
                 " Write file truncate -- need to free physical blocks.\n");
    }
    while (count) {
        uint move_count = f->pdata_end - f->pdata;

        if (move_count > count)
            move_count = count;
        memmove(f->pdata, str, move_count);
        f->pdata += move_count;
        str += move_count;
        count -= move_count;
        if (f->pdata == f->pdata_end) {
            if ((ecode = memfile_next_blk(f)) != 0) {
                f->error_code = ecode;
                if (ecode < 0)
                    return 0;
            }
        }
    }
    f->log_curr_pos += len;
    f->log_length = f->log_curr_pos;    /* truncate length to here      */
#ifdef DEBUG
    tot_raw += len;
#endif
    return (len);
}

/*                                                                      */
/*      Internal routine to set the f->pdata and f->pdata_end pointers  */
/*      for the current logical block f->log_curr_blk                   */
/*                                                                      */
/*      If data only exists in compressed form, allocate a raw buffer   */
/*      and decompress it.                                              */
/*                                                                      */

static int
memfile_get_pdata(MEMFILE * f)
{
    int code, i, num_raw_buffers, status;
    LOG_MEMFILE_BLK *bp = f->log_curr_blk;

    if (bp->phys_blk->data_limit == NULL) {
        /* Not compressed, return this data pointer                       */
        f->pdata = (bp->phys_blk)->data;
        i = f->log_curr_pos % MEMFILE_DATA_SIZE;        /* pos within block     */
        i = f->log_curr_pos - i;        /* base of block        */
        if (i + MEMFILE_DATA_SIZE > f->log_length)
            f->pdata_end = f->pdata + f->log_length - i;
        else
            f->pdata_end = f->pdata + MEMFILE_DATA_SIZE;
    } else {

        /* data was compressed                                            */
        if (f->raw_head == NULL) {
            code = 0;
            /* need to allocate the raw buffer pool                        */
            num_raw_buffers = GET_NUM_RAW_BUFFERS(f);
            if (f->reservePhysBlockCount) {
                /* HACK: allocate reserve block that's been reserved for
                 * decompression.  This buffer's block was pre-allocated to make
                 * sure we won't come up short here. Take from chain instead of
                 * allocateWithReserve() since this buf would just be wasted if
                 * allowed to remain preallocated. */
                f->raw_head = (RAW_BUFFER *)f->reservePhysBlockChain;
                f->reservePhysBlockChain = f->reservePhysBlockChain->link;
                --f->reservePhysBlockCount;
            } else {
                f->raw_head =
                    allocateWithReserve(f, sizeof(*f->raw_head), &code,
                                        "memfile raw buffer",
                        "memfile_get_pdata: MALLOC for 'raw_head' failed\n");
                if (code < 0)
                    return code;
            }
            f->raw_head->back = NULL;
            f->raw_tail = f->raw_head;
            f->raw_tail->log_blk = NULL;
            for (i = 0; i < num_raw_buffers; i++) {
                f->raw_tail->fwd = (RAW_BUFFER *) MALLOC(f, sizeof(RAW_BUFFER),
                                                      "memfile raw buffer");
                /* if MALLOC fails, then just stop allocating            */
                if (!f->raw_tail->fwd)
                    break;
                f->total_space += sizeof(RAW_BUFFER);
                f->raw_tail->fwd->back = f->raw_tail;
                f->raw_tail = f->raw_tail->fwd;
                f->raw_tail->log_blk = NULL;
            }
            f->raw_tail->fwd = NULL;
            num_raw_buffers = i + 1;    /* if MALLOC failed, then OK    */
            if_debug1(':', "[:]Number of raw buffers allocated=%d\n",
                      num_raw_buffers);
            if (f->decompress_state->templat->init != 0)
                code = (*f->decompress_state->templat->init)
                    (f->decompress_state);
            if (code < 0)
                return_error(gs_error_VMerror);

        }                       /* end allocating the raw buffer pool (first time only)           */
        if (bp->raw_block == NULL) {
#ifdef DEBUG
            tot_cache_miss++;   /* count every decompress       */
#endif
            /* find a raw buffer and decompress                            */
            if (f->raw_tail->log_blk != NULL) {
                /* This block was in use, grab it                           */
#ifdef DEBUG
                tot_swap_out++;
#endif
                f->raw_tail->log_blk->raw_block = NULL;         /* data no longer here */
                f->raw_tail->log_blk = NULL;
            }
            /* Use the last raw block in the chain (the oldest)            */
            f->raw_tail->back->fwd = NULL;      /* disconnect from tail */
            f->raw_tail->fwd = f->raw_head;     /* new head             */
            f->raw_head->back = f->raw_tail;
            f->raw_tail = f->raw_tail->back;
            f->raw_head = f->raw_head->back;
            f->raw_head->back = NULL;
            f->raw_head->log_blk = bp;

            /* Decompress the data into this raw block                     */
            /* Initialize the decompressor                              */
            if (f->decompress_state->templat->reinit != 0)
                (*f->decompress_state->templat->reinit) (f->decompress_state);
            /* Set pointers and call the decompress routine             */
            f->wt.ptr = (byte *) (f->raw_head->data) - 1;
            f->wt.limit = f->wt.ptr + MEMFILE_DATA_SIZE;
            f->rd.ptr = (const byte *)(bp->phys_pdata) - 1;
            f->rd.limit = (const byte *)bp->phys_blk->data_limit;
#ifdef DEBUG
            decomp_wt_ptr0 = f->wt.ptr;
            decomp_wt_limit0 = f->wt.limit;
            decomp_rd_ptr0 = f->rd.ptr;
            decomp_rd_limit0 = f->rd.limit;
#endif
            status = (*f->decompress_state->templat->process)
                (f->decompress_state, &(f->rd), &(f->wt), true);
            if (status == 0) {  /* More input data needed */
                /* switch to next block and continue decompress             */
                int back_up = 0;        /* adjust pointer backwards     */

                if (f->rd.ptr != f->rd.limit) {
                    /* transfer remainder bytes from the previous block      */
                    back_up = f->rd.limit - f->rd.ptr;
                    for (i = 0; i < back_up; i++)
                        *(bp->phys_blk->link->data - back_up + i) = *++f->rd.ptr;
                }
                f->rd.ptr = (const byte *)bp->phys_blk->link->data - back_up - 1;
                f->rd.limit = (const byte *)bp->phys_blk->link->data_limit;
#ifdef DEBUG
                decomp_wt_ptr1 = f->wt.ptr;
                decomp_wt_limit1 = f->wt.limit;
                decomp_rd_ptr1 = f->rd.ptr;
                decomp_rd_limit1 = f->rd.limit;
#endif
                status = (*f->decompress_state->templat->process)
                    (f->decompress_state, &(f->rd), &(f->wt), true);
                if (status == 0) {
                    emprintf(f->memory,
                             "Decompression required more than one full block!\n");
                    return_error(gs_error_Fatal);
                }
            }
            bp->raw_block = f->raw_head;        /* point to raw block           */
        }
        /* end if( raw_block == NULL ) meaning need to decompress data    */
        else {
            /* data exists in the raw data cache, if not raw_head, move it */
            if (bp->raw_block != f->raw_head) {
                /*          move to raw_head                                */
                /*          prev.fwd = this.fwd                             */
                bp->raw_block->back->fwd = bp->raw_block->fwd;
                if (bp->raw_block->fwd != NULL)
                    /*               next.back = this.back                   */
                    bp->raw_block->fwd->back = bp->raw_block->back;
                else
                    f->raw_tail = bp->raw_block->back;  /* tail = prev        */
                f->raw_head->back = bp->raw_block;      /* head.back = this     */
                bp->raw_block->fwd = f->raw_head;       /* this.fwd = orig head */
                f->raw_head = bp->raw_block;    /* head = this          */
                f->raw_head->back = NULL;       /* this.back = NULL     */
#ifdef DEBUG
                tot_cache_hits++;       /* counting here prevents repeats since */
                /* won't count if already at head       */
#endif
            }
        }
        f->pdata = bp->raw_block->data;
        f->pdata_end = f->pdata + MEMFILE_DATA_SIZE;
        /* NOTE: last block is never compressed, so a compressed block    */
        /*        is always full size.                                    */
    }                           /* end else (when data was compressed)                             */

    return 0;
}

/* ---------------- Reading ---------------- */

static int
memfile_fread_chars(void *data, uint len, clist_file_ptr cf)
{
    char *str = (char *)data;
    MEMFILE *f = (MEMFILE *) cf;
    uint count = len, num_read, move_count;

    num_read = f->log_length - f->log_curr_pos;
    if (count > num_read)
        count = num_read;
    num_read = count;

    while (count) {
        f->log_curr_pos++;      /* move into next byte */
        if (f->pdata == f->pdata_end) {
            f->log_curr_blk = (f->log_curr_blk)->link;
            memfile_get_pdata(f);
        }
        move_count = f->pdata_end - f->pdata;
        if (move_count > count)
            move_count = count;
        f->log_curr_pos += move_count - 1;      /* new position         */
        memmove(str, f->pdata, move_count);
        str += move_count;
        f->pdata += move_count;
        count -= move_count;
    }

    return (num_read);
}

/* ---------------- Position/status ---------------- */

static int
memfile_ferror_code(clist_file_ptr cf)
{
    return (((MEMFILE *) cf)->error_code);      /* errors stored here */
}

static int64_t
memfile_ftell(clist_file_ptr cf)
{
    return (((MEMFILE *) cf)->log_curr_pos);
}

static void
memfile_rewind(clist_file_ptr cf, bool discard_data, const char *ignore_fname)
{
    MEMFILE *f = (MEMFILE *) cf;

    if (discard_data) {
        /* This affects the memfile data, not just the MEMFILE * access struct */
        /* Check first to make sure that we have exclusive access */
        if (f->openlist != NULL || f->base_memfile != NULL) {
            /* TODO: Move the data so it is still connected to other open files */
            emprintf1(f->memory,
                      "memfile_rewind(%p) with discard_data=true failed: ",
                      f);
            f->error_code = gs_note_error(gs_error_ioerror);
            return;
        }
        memfile_free_mem(f);
        /* We have to call memfile_init_empty to preserve invariants. */
        memfile_init_empty(f);
    } else {
        f->log_curr_blk = f->log_head;
        f->log_curr_pos = 0;
        memfile_get_pdata(f);
    }
}

static int
memfile_fseek(clist_file_ptr cf, int64_t offset, int mode, const char *ignore_fname)
{
    MEMFILE *f = (MEMFILE *) cf;
    int64_t i, block_num, new_pos;

    switch (mode) {
        case SEEK_SET:          /* offset from the beginning of the file */
            new_pos = offset;
            break;

        case SEEK_CUR:          /* offset from the current position in the file */
            new_pos = offset + f->log_curr_pos;
            break;

        case SEEK_END:          /* offset back from the end of the file */
            new_pos = f->log_length - offset;
            break;

        default:
            return (-1);
    }
    if (new_pos < 0 || new_pos > f->log_length)
        return -1;
    if ((f->pdata == f->pdata_end) && (f->log_curr_blk->link != NULL)) {
        /* log_curr_blk is actually one block behind log_curr_pos         */
        f->log_curr_blk = f->log_curr_blk->link;
    }
    block_num = new_pos / MEMFILE_DATA_SIZE;
    i = f->log_curr_pos / MEMFILE_DATA_SIZE;
    if (block_num < i) {        /* if moving backwards, start at beginning */
        f->log_curr_blk = f->log_head;
        i = 0;
    }
    for (; i < block_num; i++) {
        f->log_curr_blk = f->log_curr_blk->link;
    }
    f->log_curr_pos = new_pos;
    memfile_get_pdata(f);       /* pointers to start of block           */
    f->pdata += new_pos - (block_num * MEMFILE_DATA_SIZE);

    return 0;                   /* return "normal" status                       */
}

/* ---------------- Internal routines ---------------- */

static void
memfile_free_mem(MEMFILE * f)
{
    LOG_MEMFILE_BLK *bp, *tmpbp;

#ifdef DEBUG
    /* output some diagnostics about the effectiveness                   */
    if (tot_raw > 100) {
        if (tot_raw > 0xFFFFFFFF)
            if_debug4(':', "[:]tot_raw=%lu%0lu, tot_compressed=%lu%0lu\n",
                      tot_raw >> 32, tot_raw & 0xFFFFFFFF,
                      tot_compressed >> 32, tot_compressed & 0xFFFFFFFF);
         else
            if_debug2(':', "[:]tot_raw=%lu, tot_compressed=%lu\n",
                      tot_raw, tot_compressed);
    }
    if (tot_cache_hits != 0) {
        if_debug3(':', "[:]Cache hits=%lu, cache misses=%lu, swapouts=%lu\n",
                 tot_cache_hits,
                 (long)(tot_cache_miss - (f->log_length / MEMFILE_DATA_SIZE)),
                 tot_swap_out);
    }
    tot_raw = 0;
    tot_compressed = 0;
    tot_cache_hits = 0;
    tot_cache_miss = 0;
    tot_swap_out = 0;
#endif

    /* Free up memory that was allocated for the memfile              */
    bp = f->log_head;

    if (bp != NULL) {
        /* Null out phys_blk pointers to compressed data. */
        PHYS_MEMFILE_BLK *pphys = bp->phys_blk;

        {
            for (tmpbp = bp; tmpbp != NULL; tmpbp = tmpbp->link)
                if (tmpbp->phys_blk->data_limit != NULL)
                    tmpbp->phys_blk = 0;
        }
        /* Free the physical blocks that make up the compressed data      */
        if (pphys->data_limit != NULL) {
            /* the data was compressed, free the chain of blocks             */
            while (pphys != NULL) {
                PHYS_MEMFILE_BLK *tmpphys = pphys->link;

                FREE(f, pphys, "memfile_free_mem(pphys)");
                pphys = tmpphys;
            }
        }
    }
    /* Now free the logical blocks, and any uncompressed physical blocks. */
    while (bp != NULL) {
        if (bp->phys_blk != NULL) {
            FREE(f, bp->phys_blk, "memfile_free_mem(phys_blk)");
        }
        tmpbp = bp->link;
        FREE(f, bp, "memfile_free_mem(log_blk)");
        bp = tmpbp;
    }

    f->log_head = NULL;

    /* Free any internal compressor state. */
    if (f->compressor_initialized) {
        if (f->decompress_state->templat->release != 0)
            (*f->decompress_state->templat->release) (f->decompress_state);
        if (f->compress_state->templat->release != 0)
            (*f->compress_state->templat->release) (f->compress_state);
        f->compressor_initialized = false;
    }
    /* free the raw buffers                                           */
    while (f->raw_head != NULL) {
        RAW_BUFFER *tmpraw = f->raw_head->fwd;

        FREE(f, f->raw_head, "memfile_free_mem(raw)");
        f->raw_head = tmpraw;
    }
}

static int
memfile_init_empty(MEMFILE * f)
{
    PHYS_MEMFILE_BLK *pphys;
    LOG_MEMFILE_BLK *plog;

   /* Zero out key fields so that allocation failure will be unwindable */
    f->phys_curr = NULL;        /* flag as file not compressed          */
    f->log_head = NULL;
    f->log_curr_blk = NULL;
    f->log_curr_pos = 0;
    f->log_length = 0;
    f->raw_head = NULL;
    f->compressor_initialized = false;
    f->total_space = 0;

    /* File empty - get a physical mem block (includes the buffer area)  */
    pphys = MALLOC(f, sizeof(*pphys), "memfile pphys");
    if (!pphys) {
        emprintf(f->memory, "memfile_init_empty: MALLOC for 'pphys' failed\n");
        return_error(gs_error_VMerror);
    }
    f->total_space += sizeof(*pphys);
    pphys->data_limit = NULL;   /* raw data for now     */

   /* Get logical mem block to go with physical one */
    plog = (LOG_MEMFILE_BLK *)MALLOC( f, sizeof(*plog), "memfile_init_empty" );
    if (plog == NULL) {
        FREE(f, pphys, "memfile_init_empty");
        emprintf(f->memory,
                 "memfile_init_empty: MALLOC for log_curr_blk failed\n");
        return_error(gs_error_VMerror);
    }
    f->total_space += sizeof(*plog);
    f->log_head = f->log_curr_blk = plog;
    f->log_curr_blk->link = NULL;
    f->log_curr_blk->phys_blk = pphys;
    f->log_curr_blk->phys_pdata = NULL;
    f->log_curr_blk->raw_block = NULL;

    f->pdata = pphys->data;
    f->pdata_end = f->pdata + MEMFILE_DATA_SIZE;

    f->error_code = 0;

    return 0;
}

clist_io_procs_t clist_io_procs_memory = {
    memfile_fopen,
    memfile_fclose,
    memfile_unlink,
    memfile_fwrite_chars,
    memfile_fread_chars,
    memfile_set_memory_warning,
    memfile_ferror_code,
    memfile_ftell,
    memfile_rewind,
    memfile_fseek,
};

init_proc(gs_gxclmem_init);
int
gs_gxclmem_init(gs_memory_t *mem)
{
    clist_io_procs_memory_global = &clist_io_procs_memory;
    return 0;
}