pgpzdeflate.c

vc环境下的pgp源码

/*
 * Copyright (C) 1990-1993 Mark Adler, Richard B. Wales, Jean-loup Gailly,
 * Kai Uwe Rommel and Igor Mandrichenko.
 * Permission is granted to any individual or institution to use, copy,
 * or redistribute this software so long as all of the original files
 * are included, that it is not sold for profit, and that this copyright
 * notice is retained.
 *
 * Hacked up for PGP by Colin Plumb
 *
 * $Id: pgpZDeflate.c,v 1.10 1997/12/12 01:14:11 heller Exp $
 */

/*
 * deflate.c by Jean-loup Gailly.
 *
 * PURPOSE
 *
 *   Identify new text as repetitions of old text within a fixed-
 *   length sliding window trailing behind the new text.
 *
 * DISCUSSION
 *
 *   The "deflation" process depends on being able to identify portions
 *   of the input text which are identical to earlier input (within a
 *   sliding window trailing behind the input currently being processed).
 *
 *   The most straightforward technique turns out to be the fastest for
 *   most input files: try all possible matches and select the longest.
 *   The key feature of this algorithm is that insertions into the string
 *   dictionary are very simple and thus fast, and deletions are avoided
 *   completely. Insertions are performed at each input character,
 *   whereas string matches are performed only when the previous match
 *   ends. So it is preferable to spend more time in matches to allow very
 *   fast string insertions and avoid deletions. The matching algorithm
 *   for small strings is inspired from that of Rabin & Karp.  A brute
 *   force approach is used to find longer strings when a small match has
 *   been found.  A similar algorithm is used in comic (by Jan-Mark Wams)
 *   and freeze (by Leonid Broukhis).
 *
 *   A previous version of this file used a more sophisticated algorithm
 *   (by Fiala and Greene) which is guaranteed to run in linear amortized
 *   time, but has a larger average cost, uses more memory and is patented.
 *   However the F&G algorithm may be faster for some highly redundant
 *   files if the parameter max_chain_length (described below) is too large.
 *
 * ACKNOWLEDGEMENTS
 *
 *   The idea of lazy evaluation of matches is due to Jan-Mark Wams, and
 *   I found it in 'freeze' written by Leonid Broukhis.
 *   Thanks to many info-zippers for bug reports and testing.
 *
 * REFERENCES
 *
 *   APPNOTE.TXT documentation file in PKZIP 1.93a distribution.
 *
 *   A description of the Rabin and Karp algorithm is given in the book
 *      "Algorithms" by R. Sedgewick, Addison-Wesley, p252.
 *
 *   Fiala,E.R., and Greene,D.H.
 *      Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595
 *
 * INTERFACE
 *
 *   int lm_init (int pack_level)
 *       Initialize the "longest match" routines for a new file
 *
 *   PGPUInt32 deflate (void)
 *       Processes a new input file and return its compressed length. Sets
 *       the compressed length, crc, deflate flags and internal file
 *       attributes.
 */

#include "pgpConfig.h"
#include "pgpContext.h"

#include "pgpZip.h"

/* ===========================================================================
 * Configuration parameters
 */

/*
 * Compile with MEDIUM_MEM to reduce the memory requirements or
 * with SMALL_MEM to use as little memory as possible. Use BIG_MEM if the
 * entire input file can be held in memory (not possible on 16 bit systems).
 * Warning: defining these symbols affects HASH_BITS (see below) and thus
 * affects the compression ratio. The compressed output
 * is still correct, and might even be smaller in some cases.
 */

#ifdef SMALL_MEM
#   define HASH_BITS  13  /* Number of bits used to hash strings */
#endif
#ifdef MEDIUM_MEM
#   define HASH_BITS  14
#endif
#ifndef HASH_BITS
#   define HASH_BITS  15
   /* For portability to 16 bit machines, do not use values above 15. */
#endif

#define HASH_SIZE (unsigned)(1<<HASH_BITS)
#define HASH_MASK (HASH_SIZE-1)
#define WMASK     (WSIZE-1)
/* HASH_SIZE and WSIZE must be powers of two */

#define NIL 0
/* Tail of hash chains */

#ifndef TOO_FAR
#  define TOO_FAR 4096
#endif
/* Matches of length 3 are discarded if their distance exceeds TOO_FAR */

#ifdef ATARI_ST
#  undef MSDOS /* avoid the processor specific parts */
   /* (but the Atari should never define MSDOS anyway ...) */
#endif
#if defined(MSDOS) && !defined(NO_ASM) && !defined(ASMV)
#  define ASMV
#endif
#if defined(ASMV) && !defined(MSDOS) && defined(DYN_ALLOC)
  error: DYN_ALLOC not yet supported in match.s
#endif

/* ===========================================================================
 * Local data used by the "longest match" routines.
 */

#if defined(BIG_MEM) || defined(MMAP)
  typedef size_t Pos; /* must be at least 32 bits */
#else
  typedef PGPUInt16 Pos;
#endif
typedef unsigned IPos;
/* A Pos is an index in the character window. We use short instead of int to
 * save space in the various tables. IPos is used only for parameter passing.
 */

/* Private context structure for use by all functions. */
typedef struct ZDeflateContext {

	PGPContextRef		cdkContext;

#ifndef DYN_ALLOC
	PGPByte window[2L*WSIZE];
	/* Sliding window.  Input bytes are read into the second half of
	 * the window, and move to the first half later to keep a
	 * dictionary of at least WSIZE bytes.  With this organization,
	 * matches are limited to a distance of WSIZE-MAX_MATCH bytes, but
	 * this ensures that IO is always performed with a length multiple
	 * of the block size.  Also, it limits the window size to 64K,
	 * which is quite useful on MSDOS.  To do: limit the window size
	 * to WSIZE+BSZ if SMALL_MEM (the code would be less efficient
	 * since the data would have to be copied WSIZE/BSZ times)
	 */
	Pos prev[WSIZE];
	/* Link to older string with same hash index. To limit the size of this
	 * array to 64K, this link is maintained only for the last 32K strings.
	 * An index in this array is thus a window index modulo 32K.
	 */
	Pos head[HASH_SIZE];
	/* Heads of the hash chains or NIL. If your compiler thinks that
	 * HASH_SIZE is a dynamic value, recompile with -DDYN_ALLOC.
	 */
#else
	/*
	 * MS-DOS adjusts the pointers for zero offset, so we store the
	 * original pointers in these variables for later free()ing
	 */
	PGPByte * near o_window;
	Pos  * near o_prev;
	Pos  * near o_head;
	PGPByte * near window;
	Pos  * near prev;
	Pos  * near head;
#endif

	PGPUInt32 window_size;
	/* window size, 2*WSIZE except for MMAP or BIG_MEM, where it is the
	 * input file length plus MIN_LOOKAHEAD.
	 */

	long block_start;
	/* window position at the beginning of the current output block. Gets
	 * negative when the window is moved backwards.
	 */

	unsigned ins_h;  /* hash index of string to be inserted */
	unsigned int near prev_length;
	/* Length of the best match at previous step. Matches not greater than this
	 * are discarded. This is used in the lazy match evaluation.
	 */

	unsigned near strstart;         /* start of string to insert */
	unsigned near match_start;      /* start of matching string */
	int           eofile;    /* flag set at end of input file */
	unsigned      lookahead; /* number of valid bytes ahead in window */

	/* Saved copies of lazy match variables */
	int s_match_available;
	int s_match_length;

	unsigned near max_chain_length;
	/* To speed up deflation, hash chains are never searched beyond
	 * this length.  A higher limit improves compression ratio but
	 * degrades the speed.
	 */

	unsigned int max_lazy_match;
	/* Attempt to find a better match only when the current match is strictly
	 * smaller than this value. This mechanism is used only for compression
	 * levels >= 4.
	 */
#define max_insert_length  max_lazy_match
	/* Insert new strings in the hash table only if the match length
	 * is not greater than this length. This saves time but degrades
	 * compression.  max_insert_length is used only for compression
	 * levels <= 3.
	 */

	unsigned near good_match;
	/* Use a faster search when the previous match is longer than this */

#ifdef  FULL_SEARCH
# define nice_match MAX_MATCH
#else
	  int near nice_match; /* Stop searching when current match exceeds this */
#endif

	/*	DEBUG_STRUCT_CONSTRUCTOR( ZDeflateContext ) */
} ZDeflateContext;


#define H_SHIFT  ((HASH_BITS+MIN_MATCH-1)/MIN_MATCH)
/* Number of bits by which ins_h and del_h must be shifted at each
 * input step. It must be such that after MIN_MATCH steps, the oldest
 * byte no longer takes part in the hash key, that is:
 *   H_SHIFT * MIN_MATCH >= HASH_BITS
 */


/* Values for max_lazy_match, good_match and max_chain_length, depending on
 * the desired pack level (0..9). The values given below have been tuned to
 * exclude worst case performance for pathological files. Better values may be
 * found for specific files.
 */

static const struct {
   PGPUInt16 good_length; /* reduce lazy search above this match length */
   PGPUInt16 max_lazy;/* don't perform lazy search above this match length */
   PGPUInt16 nice_length; /* quit search above this match length */
   PGPUInt16 max_chain;
} configuration_table[10] = {
/*      good lazy nice chain */
/* 0 */ {0,    0,  0,    0},	/* store only */
/* 1 */ {4,    4,  8,    4},	/* maximum speed, no lazy matches */
/* 2 */ {4,    5, 16,    8},
/* 3 */ {4,    6, 32,   32},

/* 4 */ {4,    4, 16,   16},	/* lazy matches */
#if 0
/* 5 */ {8,   16, 32,   32},	/* Change to new? */
#else
	{8,   64, 258, 128},	/* Match old PGP params */
#endif 
/* 6 */ {8,   16, 128, 128},
/* 7 */ {8,   32, 128, 256},
/* 8 */ {32, 128, 258, 1024},
/* 9 */ {32, 258, 258, 4096}};	/* maximum compression */

/* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4
 * For deflate_fast() (levels <= 3) good is ignored and lazy has a different
 * meaning.
 */

/* ===========================================================================
 *  Prototypes for local functions.
 */

static void slide_window(ZDeflateContext *);
static int deflate_sub(ZDeflateContext *, struct ZTreesContext *,
	struct ZBitsContext *);

int  longest_match(ZDeflateContext *, IPos cur_match);
#ifdef ASMV
void match_init(void); /* asm code initialization */
#endif

#ifdef ZIPDEBUG
static void check_match(ZDeflateContext *, IPos start, IPos match, int length);
#endif

/* ===========================================================================
 * Update a hash value with the given input byte
 * IN  assertion: all calls to to UPDATE_HASH are made with consecutive
 *    input characters, so that a running hash key can be computed from the
 *    previous key instead of complete recalculation each time.
 */
#define UPDATE_HASH(h,c) (h = (((h)<<H_SHIFT) ^ (c)) & HASH_MASK)

/* ===========================================================================
 * Insert string s in the dictionary and set match_head to the previous head
 * of the hash chain (the most recent string with same hash key). Return
 * the previous length of the hash chain.
 * IN  assertion: all calls to to INSERT_STRING are made with consecutive
 *    input characters and the first MIN_MATCH bytes of s are valid
 *    (except for the last MIN_MATCH-1 bytes of the input file).
 */
#define INSERT_STRING(ctx, s, match_head) \
  (UPDATE_HASH((ctx)->ins_h, (ctx)->window[(s) + MIN_MATCH-1]), \
  (ctx)->prev[(s) & WMASK] = (Pos)((match_head) = (ctx)->head[(ctx)->ins_h]), \
  (ctx)->head[(ctx)->ins_h] = (Pos)(s))

/* ===========================================================================
 * Initialize the "longest match" routines for a new file
 *
 * IN assertion: window_size is > 0 if the input file is already read or
 *    mmap'ed in the window[] array, 0 otherwise. In the first case,
 *    window_size is sufficient to contain the whole input file plus
 *    MIN_LOOKAHEAD bytes (to avoid referencing memory beyond the end
 *    of window[] when looking for matches towards the end).
 */
ZDeflateContext *
lm_init(PGPContextRef cdkContext, int pack_level)
	/* 0: store, 1: best speed, 9: best compression */
{
	ZDeflateContext *ctx;

    if (pack_level < 1 || pack_level > 9)
		return NULL;
	/* error("bad pack level"); */

	ctx = (ZDeflateContext *) pgpContextMemAlloc (cdkContext, 
								sizeof(*ctx), kPGPMemoryMgrFlags_Clear);
	if (IsNull (ctx) )
		return NULL;
	ctx->cdkContext = cdkContext;

    /* Do not slide the window if the whole input is already in memory
     * (window_size > 0)
     */
    if (ctx->window_size == 0)
		ctx->window_size = (PGPUInt32)2*WSIZE;

    /* Use dynamic allocation if compiler does not like big static arrays: */
    /* The +8 is for MS-DOS, so the pointers can be segment-aligned */
#ifdef DYN_ALLOC
	pgpAssert (ctx->o_window == NULL);
	ctx->window = ctx->o_window = (PGPByte *)pgpContextMemAlloc (cdkContext,
						(WSIZE+8)*2*sizeof(PGPByte), kPGPMemoryMgrFlags_Clear);
	if (ctx->o_window == NULL) {
		pgpContextMemFree (cdkContext, ctx);
		return NULL;
		/* err(ZE_MEM, "window allocation"); */
	}
	pgpAssert (ctx->o_prev == NULL);
	ctx->prev = ctx->o_prev = (Pos*) pgpContextMemAlloc (cdkContext,
				(WSIZE+8) * sizeof(Pos), kPGPMemoryMgrFlags_Clear);
	ctx->head = ctx->o_head = (Pos*) pgpContextMemAlloc (cdkContext,
				(HASH_SIZE+8) * sizeof(Pos), kPGPMemoryMgrFlags_Clear);
	if (ctx->o_prev == NULL || ctx->o_head == NULL) {
		if (ctx->o_prev)
			pgpContextMemFree (cdkContext, ctx->o_prev);
		pgpContextMemFree (cdkContext, ctx->o_window);
		pgpContextMemFree (cdkContext, ctx);
		return NULL;
		/* err(ZE_MEM, "hash table allocation"); */
	}
#endif /* DYN_ALLOC */

    /* Initialize the hash table (avoiding 64K overflow for 16 bit systems).
     * prev[] will be initialized on the fly.
     */
    ctx->head[HASH_SIZE-1] = NIL;
    pgpClearMemory((char*)ctx->head, (unsigned)(HASH_SIZE-1)*
				   					sizeof(*ctx->head));

    /* Set the default configuration parameters:
     */
    ctx->max_lazy_match   = configuration_table[pack_level].max_lazy;
    ctx->good_match       = configuration_table[pack_level].good_length;
#ifndef FULL_SEARCH
    ctx->nice_match       = configuration_table[pack_level].nice_length;
#endif
    ctx->max_chain_length = configuration_table[pack_level].max_chain;
    /* ??? reduce max_chain_length for binary files */

    ctx->strstart = 0;
    ctx->block_start = 0L;
#ifdef ASMV
    match_init(ctx); /* initialize the asm code */
#endif

    ctx->lookahead = 0;
    ctx->eofile = 0;

    ctx->s_match_available = 0; /* set if previous match exists */
    ctx->s_match_length = MIN_MATCH-1; /* length of best match */

    return ctx;
}

/* ===========================================================================
 * Free the window and hash table
 */
void