root/vowfsc/xdelta3.h

/* xdelta 3 - delta compression tools and library
 * Copyright (C) 2001, 2003, 2004, 2005, 2006.  Joshua P. MacDonald
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/* Welcome to Xdelta.  If you want to know more about Xdelta, start by reading xdelta3.c.
 * If you are ready to use the API, continue reading here.  There are two interfaces --
 * xd3_encode_input and xd3_decode_input -- plus a dozen or so related calls.  This
 * interface is styled after Zlib. */

#ifndef _XDELTA3_H_
#define _XDELTA3_H_

#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

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

/* Default configured value of stream->winsize.  If the program supplies
 * xd3_encode_input() with data smaller than winsize the stream will
 * automatically buffer the input, otherwise the input buffer is used directly.
 */
#ifndef XD3_DEFAULT_WINSIZE
#define XD3_DEFAULT_WINSIZE (1U << 23)
#endif

/* Default total size of the source window used in xdelta3-main.h */
#ifndef XD3_DEFAULT_SRCWINSZ
#define XD3_DEFAULT_SRCWINSZ (1U << 26)
#endif

/* When Xdelta requests a memory allocation for certain buffers, it rounds up to units of
 * at least this size.  The code assumes (and asserts) that this is a power-of-two. */
#ifndef XD3_ALLOCSIZE
#define XD3_ALLOCSIZE (1U<<14)
#endif

/* The XD3_HARDMAXWINSIZE parameter is a safety mechanism to protect decoders against
 * malicious files.  The decoder will never decode a window larger than this.  If the file
 * specifies VCD_TARGET the decoder may require two buffers of this size.
 *
 * 8-16MB is reasonable, probably don't need to go larger. */
#ifndef XD3_HARDMAXWINSIZE
#define XD3_HARDMAXWINSIZE (1U<<24)
#endif
/* The IOPT_SIZE value sets the size of a buffer used to batch overlapping copy
 * instructions before they are optimized by picking the best non-overlapping ranges.  The
 * larger this buffer, the longer a forced xd3_srcwin_setup() decision is held off.
 * Setting this value to 0 causes an unlimited buffer to be used. */
#ifndef XD3_DEFAULT_IOPT_SIZE
#define XD3_DEFAULT_IOPT_SIZE    (1U<<15)
#endif

/* The maximum distance backward to search for small matches */
#ifndef XD3_DEFAULT_SPREVSZ
#define XD3_DEFAULT_SPREVSZ (1U<<18)
#endif

/* The default compression level
 */
#ifndef XD3_DEFAULT_LEVEL
#define XD3_DEFAULT_LEVEL 1
#endif

/* Sizes and addresses within VCDIFF windows are represented as usize_t
 *
 * For source-file offsets and total file sizes, total input and output counts, the xoff_t
 * type is used.  The decoder and encoder generally check for overflow of the xoff_t size,
 * and this is tested at the 32bit boundary [xdelta3-test.h].
 */
#ifndef _WIN32
typedef unsigned int    usize_t;
typedef u_int8_t        uint8_t;
typedef u_int16_t       uint16_t;

#ifndef __uint32_t_defined  /* Note: Cygwin compat */
typedef u_int32_t       uint32_t;
#endif

typedef long long unsigned int uint64_t;

#else
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#define inline
typedef unsigned int   uint;
typedef signed int     ssize_t;
typedef unsigned int   usize_t;
typedef unsigned char  uint8_t;
typedef unsigned short uint16_t;
typedef unsigned long  uint32_t;
typedef ULONGLONG      uint64_t;
#endif

#define SIZEOF_USIZE_T 4

#ifndef XD3_USE_LARGEFILE64
#define XD3_USE_LARGEFILE64 1
#endif

#if XD3_USE_LARGEFILE64
#define __USE_FILE_OFFSET64 1 /* GLIBC: for 64bit fileops, ... ? */
typedef uint64_t xoff_t;
#define SIZEOF_XOFF_T 8
#else
typedef uint32_t xoff_t;
#define SIZEOF_XOFF_T 4
#endif

#define USE_UINT32 (SIZEOF_USIZE_T == 4 || SIZEOF_XOFF_T == 4 || REGRESSION_TEST)
#define USE_UINT64 (SIZEOF_USIZE_T == 8 || SIZEOF_XOFF_T == 8 || REGRESSION_TEST)

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

#ifndef INLINE
#define INLINE inline
#endif

/* Whether to build the encoder, otherwise only build the decoder. */
#ifndef XD3_ENCODER
#define XD3_ENCODER 1
#endif

/* The code returned when main() fails, also defined in system includes. */
#ifndef EXIT_FAILURE
#define EXIT_FAILURE 1
#endif

/* REGRESSION TEST enables the "xdelta3 test" command, which runs a series of self-tests. */
#ifndef REGRESSION_TEST
#define REGRESSION_TEST 0
#endif

/* XD3_DEBUG=1 enables assertions and various statistics.  Levels > 1 enable some
 * additional output only useful during development and debugging. */
#ifndef XD3_DEBUG
#define XD3_DEBUG 0
#endif

#ifndef PYTHON_MODULE
#define PYTHON_MODULE 0
#endif

#ifndef SWIG_MODULE
#define SWIG_MODULE 0
#endif

/* There are three string matching functions supplied: one fast, one slow (default), and
 * one soft-configurable.  To disable any of these, use the following definitions. */
#ifndef XD3_BUILD_SLOW
#define XD3_BUILD_SLOW 1
#endif
#ifndef XD3_BUILD_FAST
#define XD3_BUILD_FAST 1
#endif
#ifndef XD3_BUILD_FASTEST
#define XD3_BUILD_FASTEST 1
#endif
#ifndef XD3_BUILD_SOFT
#define XD3_BUILD_SOFT 1
#endif
#ifndef XD3_BUILD_DEFAULT
#define XD3_BUILD_DEFAULT 1
#endif

#if XD3_DEBUG
#include <stdio.h>
#endif

/* XPRINT.  Debug output and VCDIFF_TOOLS functions report to stderr.  I have used an
 * irregular style to abbreviate [fprintf(stderr, "] as [DP(RINT "]. */
#define DP   fprintf
#define RINT stderr,

typedef struct _xd3_stream             xd3_stream;
typedef struct _xd3_source             xd3_source;
typedef struct _xd3_hash_cfg           xd3_hash_cfg;
typedef struct _xd3_smatcher           xd3_smatcher;
typedef struct _xd3_rinst              xd3_rinst;
typedef struct _xd3_dinst              xd3_dinst;
typedef struct _xd3_hinst              xd3_hinst;
typedef struct _xd3_rpage              xd3_rpage;
typedef struct _xd3_addr_cache         xd3_addr_cache;
typedef struct _xd3_output             xd3_output;
typedef struct _xd3_desect             xd3_desect;
typedef struct _xd3_iopt_buflist       xd3_iopt_buflist;
typedef struct _xd3_rlist              xd3_rlist;
typedef struct _xd3_sec_type           xd3_sec_type;
typedef struct _xd3_sec_cfg            xd3_sec_cfg;
typedef struct _xd3_sec_stream         xd3_sec_stream;
typedef struct _xd3_config             xd3_config;
typedef struct _xd3_code_table_desc    xd3_code_table_desc;
typedef struct _xd3_code_table_sizes   xd3_code_table_sizes;
typedef struct _xd3_slist              xd3_slist;

/* The stream configuration has three callbacks functions, all of which may be supplied
 * with NULL values.  If config->getblk is provided as NULL, the stream returns
 * XD3_GETSRCBLK. */

typedef void*  (xd3_alloc_func)    (void       *opaque,
                                    usize_t      items,
                                    usize_t      size);
typedef void   (xd3_free_func)     (void       *opaque,
                                    void       *address);

typedef int    (xd3_getblk_func)   (xd3_stream *stream,
                                    xd3_source *source,
                                    xoff_t      blkno);

/* These are internal functions to delay construction of encoding tables and support
 * alternate code tables.  See the comments & code enabled by GENERIC_ENCODE_TABLES. */

typedef const xd3_dinst* (xd3_code_table_func) (void);
typedef int              (xd3_comp_table_func) (xd3_stream *stream,
                                                const uint8_t **data,
                                                usize_t *size);


/* Some junk. */

#ifndef XD3_ASSERT
#if XD3_DEBUG
#define XD3_ASSERT(x) \
    do { if (! (x)) { DP(RINT "%s:%d: XD3 assertion failed: %s\n", __FILE__, __LINE__, #x); \
    abort (); } } while (0)
#else
#define XD3_ASSERT(x) (void)0
#endif
#endif

#ifdef __GNUC__
/* As seen on linux-kernel. */
#ifndef max
#define max(x,y) ({ \
        const typeof(x) _x = (x);       \
        const typeof(y) _y = (y);       \
        (void) (&_x == &_y);            \
        _x > _y ? _x : _y; })
#endif

#ifndef min
#define min(x,y) ({ \
        const typeof(x) _x = (x);       \
        const typeof(y) _y = (y);       \
        (void) (&_x == &_y);            \
        _x < _y ? _x : _y; })
#endif
#else
#ifndef max
#define max(x,y) ((x) < (y) ? (y) : (x))
#endif
#ifndef min
#define min(x,y) ((x) < (y) ? (x) : (y))
#endif
#endif

/******************************************************************************************
 PUBLIC ENUMS
 ******************************************************************************************/

/* These are the five ordinary status codes returned by the xd3_encode_input() and
 * xd3_decode_input() state machines. */
typedef enum {

  /* An application must be prepared to handle these five return values from either
   * xd3_encode_input or xd3_decode_input, except in the case of no-source compression, in
   * which case XD3_GETSRCBLK is never returned.  More detailed comments for these are
   * given in xd3_encode_input and xd3_decode_input comments, below. */
  XD3_INPUT     = -17703, /* need input */
  XD3_OUTPUT    = -17704, /* have output */
  XD3_GETSRCBLK = -17705, /* need a block of source input (with no xd3_getblk function),
                           * a chance to do non-blocking read. */
  XD3_GOTHEADER = -17706, /* (decode-only) after the initial VCDIFF & first window header */
  XD3_WINSTART  = -17707, /* notification: returned before a window is processed, giving a
                           * chance to XD3_SKIP_WINDOW or not XD3_SKIP_EMIT that window. */
  XD3_WINFINISH  = -17708, /* notification: returned after encode/decode & output for a window */
  XD3_TOOFARBACK = -17709, /* (encoder only) may be returned by getblk() if the block is too old */
  XD3_INTERNAL   = -17710, /* internal error */
  XD3_INVALID    = -17711, /* invalid config */
  XD3_INVALID_INPUT = -17712, /* invalid input/decoder error */
  XD3_NOSECOND  = -17713, /* when secondary compression finds no improvement. */

} xd3_rvalues;

/* special values in config->flags */
typedef enum
{
  XD3_JUST_HDR       = (1 << 1),   /* used by VCDIFF tools, see xdelta3-main.h. */
  XD3_SKIP_WINDOW    = (1 << 2),   /* used by VCDIFF tools, see xdelta3-main.h. */
  XD3_SKIP_EMIT      = (1 << 3),   /* used by VCDIFF tools, see xdelta3-main.h. */
  XD3_FLUSH          = (1 << 4),   /* flush the stream buffer to prepare for xd3_stream_close(). */

  XD3_SEC_DJW        = (1 << 5),   /* use DJW static huffman */
  XD3_SEC_FGK        = (1 << 6),   /* use FGK adaptive huffman */
  XD3_SEC_TYPE       = (XD3_SEC_DJW | XD3_SEC_FGK),

  XD3_SEC_NODATA     = (1 << 7),   /* disable secondary compression of the data section. */
  XD3_SEC_NOINST     = (1 << 8),   /* disable secondary compression of the inst section. */
  XD3_SEC_NOADDR     = (1 << 9),   /* disable secondary compression of the addr section. */

  XD3_SEC_OTHER      = (XD3_SEC_NODATA | XD3_SEC_NOINST | XD3_SEC_NOADDR),

  XD3_ADLER32        = (1 << 10),  /* enable checksum computation in the encoder. */
  XD3_ADLER32_NOVER  = (1 << 11),  /* disable checksum verification in the decoder. */

  XD3_ALT_CODE_TABLE = (1 << 12),  /* for testing the alternate code table encoding. */

  XD3_NOCOMPRESS     = (1 << 13),  /* disable ordinary data compression feature,
                                    * only search the source, not the target. */
  XD3_BEGREEDY       = (1 << 14),  /* disable the "1.5-pass algorithm", instead use
                                    * greedy matching.  Greedy is off by default. */

  /* 4 bits to set the compression level the same as the command-line
   * setting -1 through -9 (-0 corresponds to the XD3_NOCOMPRESS flag,
   * and is independent of compression level).  This is for
   * convenience, especially with xd3_encode_memory(). */

  XD3_COMPLEVEL_SHIFT = 20,  /* 20 - 24 */
  XD3_COMPLEVEL_MASK = (0xF << XD3_COMPLEVEL_SHIFT),
  XD3_COMPLEVEL_1 = (1 << XD3_COMPLEVEL_SHIFT),
  XD3_COMPLEVEL_3 = (3 << XD3_COMPLEVEL_SHIFT),
  XD3_COMPLEVEL_6 = (6 << XD3_COMPLEVEL_SHIFT),
  XD3_COMPLEVEL_9 = (9 << XD3_COMPLEVEL_SHIFT),

} xd3_flags;

/* The values of this enumeration are set in xd3_config using the
 * smatch_cfg variable.  It can be set to default, slow, fast, etc.,
 * and soft. */
typedef enum
{
  XD3_SMATCH_DEFAULT = 0, /* Flags may contain XD3_COMPLEVEL bits, else default. */
  XD3_SMATCH_SLOW    = 1,
  XD3_SMATCH_FAST    = 2,
  XD3_SMATCH_FASTEST = 3,
  XD3_SMATCH_SOFT    = 4,
} xd3_smatch_cfg;

/******************************************************************************************
 PRIVATE ENUMS
 ******************************************************************************************/

/* stream->match_state is part of the xd3_encode_input state machine for source matching:
 *
 *  1. the XD3_GETSRCBLK block-read mechanism means reentrant matching
 *  2. this state spans encoder windows: a match and end-of-window will continue in the next
 *  3. the initial target byte and source byte are a presumed match, to avoid some computation
 *  in case the inputs are identical.
 */
typedef enum {

  MATCH_TARGET    = 0, /* in this state, attempt to match the start of the target with the
                        * previously set source address (initially 0). */
  MATCH_BACKWARD  = 1, /* currently expanding a match backward in the source/target. */
  MATCH_FORWARD   = 2, /* currently expanding a match forward in the source/target. */
  MATCH_SEARCHING = 3, /* currently searching for a match. */

} xd3_match_state;

/* The xd3_encode_input state machine steps through these states in the following order.
 * The matcher is reentrant and returns XD3_INPUT whenever it requires more data.  After
 * receiving XD3_INPUT, if the application reads EOF it should call xd3_stream_close().
 */
typedef enum {

  ENC_INIT      = 0, /* xd3_encode_input has never been called. */
  ENC_INPUT     = 1, /* waiting for xd3_avail_input () to be called. */
  ENC_SEARCH    = 2, /* currently searching for matches. */
  ENC_FLUSH     = 3, /* currently emitting output. */
  ENC_POSTOUT   = 4, /* after an output section. */
  ENC_POSTWIN   = 5, /* after all output sections. */
  ENC_ABORTED   = 6, /* abort. */
} xd3_encode_state;

/* The xd3_decode_input state machine steps through these states in the following order.
 * The matcher is reentrant and returns XD3_INPUT whenever it requires more data.  After
 * receiving XD3_INPUT, if the application reads EOF it should call xd3_stream_close().
 *
 * 0-8:   the VCDIFF header
 * 9-18:  the VCDIFF window header
 * 19-21: the three primary sections: data (which I think should have gone last), inst, addr
 * 22:    producing output: returns XD3_OUTPUT, possibly XD3_GETSRCBLK,
 * 23:    return XD3_WINFINISH, set state=9 to decode more input
 */
typedef enum {

  DEC_VCHEAD   = 0, /* VCDIFF header */
  DEC_HDRIND   = 1, /* header indicator */

  DEC_SECONDID = 2, /* secondary compressor ID */

  DEC_TABLEN   = 3, /* code table length */
  DEC_NEAR     = 4, /* code table near */
  DEC_SAME     = 5, /* code table same */
  DEC_TABDAT   = 6, /* code table data */

  DEC_APPLEN   = 7, /* application data length */
  DEC_APPDAT   = 8, /* application data */

  DEC_WININD   = 9, /* window indicator */

  DEC_CPYLEN   = 10, /* copy window length */
  DEC_CPYOFF   = 11, /* copy window offset */

  DEC_ENCLEN   = 12, /* length of delta encoding */
  DEC_TGTLEN   = 13, /* length of target window */
  DEC_DELIND   = 14, /* delta indicator */

  DEC_DATALEN  = 15, /* length of ADD+RUN data */
  DEC_INSTLEN  = 16, /* length of instruction data */
  DEC_ADDRLEN  = 17, /* length of address data */

  DEC_CKSUM    = 18, /* window checksum */

  DEC_DATA     = 19, /* data section */
  DEC_INST     = 20, /* instruction section */
  DEC_ADDR     = 21, /* address section */

  DEC_EMIT     = 22, /* producing data */

  DEC_FINISH   = 23, /* window finished */

  DEC_ABORTED  = 24, /* xd3_abort_stream */
} xd3_decode_state;

/******************************************************************************************
 internal types
 ******************************************************************************************/

/* instruction lists used in the IOPT buffer */
struct _xd3_rlist
{
  xd3_rlist  *next;
  xd3_rlist  *prev;
};

/* the raw encoding of an instruction used in the IOPT buffer */
struct _xd3_rinst
{
  uint8_t     type;
  uint8_t     xtra;
  uint8_t     code1;
  uint8_t     code2;
  usize_t      pos;
  usize_t      size;
  xoff_t      addr;
  xd3_rlist   link;
};

/* the code-table form of an single- or double-instruction */
struct _xd3_dinst
{
  uint8_t     type1;
  uint8_t     size1;
  uint8_t     type2;
  uint8_t     size2;
};

/* the decoded form of a single (half) instruction. */
struct _xd3_hinst
{
  uint8_t     type;
  uint32_t    size;
  uint32_t    addr;
};

/* used by the encoder to buffer output in sections.  list of blocks. */
struct _xd3_output
{
  uint8_t    *base;
  usize_t     next;
  usize_t     avail;
  xd3_output *next_page;
};

/* used by the decoder to buffer input in sections. */
struct _xd3_desect
{
  const uint8_t *buf;
  const uint8_t *buf_max;
  uint32_t       size;
  usize_t        pos;

  /* used in xdelta3-decode.h */
  uint8_t       *copied1;
  usize_t        alloc1;

  /* used in xdelta3-second.h */
  uint8_t       *copied2;
  usize_t        alloc2;
};

/* the VCDIFF address cache, see the RFC */
struct _xd3_addr_cache
{
  uint     s_near;
  uint     s_same;
  usize_t  next_slot;  /* the circular index for near */
  usize_t *near_array; /* array of size s_near        */
  usize_t *same_array; /* array of size s_same*256    */
};

/* the IOPT buffer list is just a list of buffers, which may be allocated
 * during encode when using an unlimited buffer. */
struct _xd3_iopt_buflist
{
  xd3_rinst *buffer;
  xd3_iopt_buflist *next;
};

/* This is the record of a pre-compiled configuration, a subset of xd3_config. */
struct _xd3_smatcher
{
  const char        *name;
  int             (*string_match) (xd3_stream  *stream);
  uint               large_look;
  uint               large_step;
  uint               small_look;
  uint               small_chain;
  uint               small_lchain;
  uint               max_lazy;
  uint               long_enough;
};

/* hash table size & power-of-two hash function. */
struct _xd3_hash_cfg
{
  usize_t           size;
  usize_t           shift;
  usize_t           mask;
};

/* the sprev list */
struct _xd3_slist
{
  usize_t     last_pos;
};

/******************************************************************************************
 public types
 ******************************************************************************************/

/* Settings for the secondary compressor. */
struct _xd3_sec_cfg
{
  int                data_type;     /* Which section. (set automatically) */
  int                ngroups;       /* Number of DJW Huffman groups. */
  int                sector_size;   /* Sector size. */
  int                inefficient;   /* If true, ignore efficiency check [avoid XD3_NOSECOND]. */
};

/* This is the user-visible stream configuration. */
struct _xd3_config
{
  usize_t             winsize;       /* The encoder window size. */
  usize_t             sprevsz;       /* How far back small string matching goes */
  usize_t             iopt_size;     /* entries in the instruction-optimizing buffer */
  usize_t             srcwin_maxsz;  /* srcwin_size grows by a factor of 2 when no matches are found */

  xd3_getblk_func   *getblk;        /* The three callbacks. */
  xd3_alloc_func    *alloc;
  xd3_free_func     *freef;
  void              *opaque;        /* Not used. */
  int                flags;         /* stream->flags are initialized from xd3_config &
                                     * never modified by the library.  Use xd3_set_flags
                                     * to modify flags settings mid-stream. */

  xd3_sec_cfg       sec_data;       /* Secondary compressor config: data */
  xd3_sec_cfg       sec_inst;       /* Secondary compressor config: inst */
  xd3_sec_cfg       sec_addr;       /* Secondary compressor config: addr */

  xd3_smatch_cfg     smatch_cfg;    /* See enum: use fields below for soft config */
  xd3_smatcher       smatcher_soft;
};

/* The primary source file object. You create one of these objects and initialize the
 * first four fields.  This library maintains the next 5 fields.  The configured getblk
 * implementation is responsible for setting the final 3 fields when called (and/or when
 * XD3_GETSRCBLK is returned).
 */
struct _xd3_source
{
  /* you set */
  xoff_t              size;          /* size of this source */
  usize_t             blksize;       /* block size */
  const char         *name;          /* its name, for debug/print purposes */
  void               *ioh;           /* opaque handle */

  /* getblk sets */
  xoff_t              curblkno;      /* current block number: client sets after getblk request */
  usize_t             onblk;         /* number of bytes on current block: client sets, xd3 verifies */
  const uint8_t      *curblk;        /* current block array: client sets after getblk request */

  /* xd3 sets */
  usize_t             srclen;        /* length of this source window */
  xoff_t              srcbase;       /* offset of this source window in the source itself */
  xoff_t              blocks;        /* the total number of blocks in this source */
  usize_t             cpyoff_blocks; /* offset of copy window in blocks */
  usize_t             cpyoff_blkoff; /* offset of copy window in blocks, remainder */
  xoff_t              getblkno;      /* request block number: xd3 sets current getblk request */
};

/* The primary xd3_stream object, used for encoding and decoding.  You may access only two
 * fields: avail_out, next_out.  Use the methods above to operate on xd3_stream. */
struct _xd3_stream
{
  /* input state */
  const uint8_t    *next_in;          /* next input byte */
  usize_t           avail_in;         /* number of bytes available at next_in */
  xoff_t            total_in;         /* how many bytes in */

  /* output state */
  uint8_t          *next_out;         /* next output byte */
  usize_t           avail_out;        /* number of bytes available at next_out */
  usize_t           space_out;        /* total out space */
  xoff_t            current_window;   /* number of windows encoded/decoded */
  xoff_t            total_out;        /* how many bytes out */

  /* to indicate an error, xd3 sets */
  const char       *msg;              /* last error message, NULL if no error */

  /* source configuration */
  xd3_source       *src;              /* source array */

  /* encoder memory configuration */
  usize_t           winsize;          /* suggested window size */
  usize_t           sprevsz;          /* small string, previous window size (power of 2) */
  usize_t           sprevmask;        /* small string, previous window size mask */
  uint              iopt_size;
  uint              iopt_unlimited;
  uint              srcwin_maxsz;

  /* general configuration */
  xd3_getblk_func  *getblk;           /* set nxtblk, nxtblkno to scanblkno */
  xd3_alloc_func   *alloc;            /* malloc function */
  xd3_free_func    *free;             /* free function */
  void*             opaque;           /* private data object passed to alloc, free, and getblk */
  int               flags;            /* various options */
  
  /* secondary compressor configuration */
  xd3_sec_cfg       sec_data;         /* Secondary compressor config: data */
  xd3_sec_cfg       sec_inst;         /* Secondary compressor config: inst */
  xd3_sec_cfg       sec_addr;         /* Secondary compressor config: addr */

  xd3_smatcher      smatcher;

  usize_t           *large_table;      /* table of large checksums */
  xd3_hash_cfg       large_hash;       /* large hash config */

  usize_t           *small_table;      /* table of small checksums */
  xd3_slist         *small_prev;       /* table of previous offsets, circular linked list */
  int                small_reset;      /* true if small table should be reset */

  xd3_hash_cfg       small_hash;       /* small hash config */
  xd3_addr_cache     acache;           /* the vcdiff address cache */
  xd3_encode_state   enc_state;        /* state of the encoder */

  usize_t            taroff;           /* base offset of the target input */
  usize_t            input_position;   /* current input position */
  usize_t            min_match;        /* current minimum match length, avoids redundent matches */
  usize_t            unencoded_offset; /* current input, first unencoded offset. this value is <= the first
                                       * instruction's position in the iopt buffer, if there is at least one
                                       * match in the buffer. */

  // SRCWIN
  // these variables plus srcwin_maxsz above (set by config)
  int