zlib.c

经典的ppp程序

#ifdef DEBUG_ZLIB
    ulg bits_sent;      /* bit length of the compressed data */
#endif

    ush bi_buf;
    /* Output buffer. bits are inserted starting at the bottom (least
     * significant bits).
     */
    int bi_valid;
    /* Number of valid bits in bi_buf.  All bits above the last valid bit
     * are always zero.
     */

    uInt blocks_in_packet;
    /* Number of blocks produced since the last time Z_PACKET_FLUSH
     * was used.
     */

} FAR deflate_state;

/* Output a byte on the stream.
 * IN assertion: there is enough room in pending_buf.
 */
#define put_byte(s, c) {s->pending_buf[s->pending++] = (c);}


#define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
/* Minimum amount of lookahead, except at the end of the input file.
 * See deflate.c for comments about the MIN_MATCH+1.
 */

#define MAX_DIST(s)  ((s)->w_size-MIN_LOOKAHEAD)
/* In order to simplify the code, particularly on 16 bit machines, match
 * distances are limited to MAX_DIST instead of WSIZE.
 */

        /* in trees.c */
local void ct_init       OF((deflate_state *s));
local int  ct_tally      OF((deflate_state *s, int dist, int lc));
local ulg ct_flush_block OF((deflate_state *s, charf *buf, ulg stored_len,
			     int flush));
local void ct_align      OF((deflate_state *s));
local void ct_stored_block OF((deflate_state *s, charf *buf, ulg stored_len,
                          int eof));
local void ct_stored_type_only OF((deflate_state *s));


/*+++++*/
/* deflate.c -- compress data using the deflation algorithm
 * Copyright (C) 1995 Jean-loup Gailly.
 * For conditions of distribution and use, see copyright notice in zlib.h 
 */

/*
 *  ALGORITHM
 *
 *      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 people for bug reports and testing.
 *
 *  REFERENCES
 *
 *      Deutsch, L.P.,"'Deflate' Compressed Data Format Specification".
 *      Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc
 *
 *      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
 *
 */

/* From: deflate.c,v 1.8 1995/05/03 17:27:08 jloup Exp */

local char zlib_copyright[] = " deflate Copyright 1995 Jean-loup Gailly ";
/*
  If you use the zlib library in a product, an acknowledgment is welcome
  in the documentation of your product. If for some reason you cannot
  include such an acknowledgment, I would appreciate that you keep this
  copyright string in the executable of your product.
 */

#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 */

#define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
/* Minimum amount of lookahead, except at the end of the input file.
 * See deflate.c for comments about the MIN_MATCH+1.
 */

/* 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.
 */

typedef struct config_s {
   ush good_length; /* reduce lazy search above this match length */
   ush max_lazy;    /* do not perform lazy search above this match length */
   ush nice_length; /* quit search above this match length */
   ush max_chain;
} config;

local config 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 */
/* 5 */ {8,   16, 32,   32},
/* 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.
 */

#define EQUAL 0
/* result of memcmp for equal strings */

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

local void fill_window   OF((deflate_state *s));
local int  deflate_fast  OF((deflate_state *s, int flush));
local int  deflate_slow  OF((deflate_state *s, int flush));
local void lm_init       OF((deflate_state *s));
local int longest_match  OF((deflate_state *s, IPos cur_match));
local void putShortMSB   OF((deflate_state *s, uInt b));
local void flush_pending OF((z_stream *strm));
local int read_buf       OF((z_stream *strm, charf *buf, unsigned size));
#ifdef ASMV
      void match_init OF((void)); /* asm code initialization */
#endif

#ifdef DEBUG_ZLIB
local  void check_match OF((deflate_state *s, 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(s,h,c) (h = (((h)<<s->hash_shift) ^ (c)) & s->hash_mask)


/* ===========================================================================
 * Insert string str 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 str are valid
 *    (except for the last MIN_MATCH-1 bytes of the input file).
 */
#define INSERT_STRING(s, str, match_head) \
   (UPDATE_HASH(s, s->ins_h, s->window[(str) + (MIN_MATCH-1)]), \
    s->prev[(str) & s->w_mask] = match_head = s->head[s->ins_h], \
    s->head[s->ins_h] = (str))

/* ===========================================================================
 * Initialize the hash table (avoiding 64K overflow for 16 bit systems).
 * prev[] will be initialized on the fly.
 */
#define CLEAR_HASH(s) \
    s->head[s->hash_size-1] = NIL; \
    zmemzero((charf *)s->head, (unsigned)(s->hash_size-1)*sizeof(*s->head));

/* ========================================================================= */
int deflateInit (strm, level)
    z_stream *strm;
    int level;
{
    return deflateInit2 (strm, level, DEFLATED, MAX_WBITS, DEF_MEM_LEVEL,
			 0, 0);
    /* To do: ignore strm->next_in if we use it as window */
}

/* ========================================================================= */
int deflateInit2 (strm, level, method, windowBits, memLevel,
		  strategy, minCompression)
    z_stream *strm;
    int  level;
    int  method;
    int  windowBits;
    int  memLevel;
    int  strategy;
    int  minCompression;
{
    deflate_state *s;
    int noheader = 0;

    if (strm == Z_NULL) return Z_STREAM_ERROR;

    strm->msg = Z_NULL;
/*    if (strm->zalloc == Z_NULL) strm->zalloc = zcalloc; */
/*    if (strm->zfree == Z_NULL) strm->zfree = zcfree; */

    if (level == Z_DEFAULT_COMPRESSION) level = 6;

    if (windowBits < 0) { /* undocumented feature: suppress zlib header */
        noheader = 1;
        windowBits = -windowBits;
    }
    if (memLevel < 1 || memLevel > MAX_MEM_LEVEL || method != DEFLATED ||
        windowBits < 8 || windowBits > 15 || level < 1 || level > 9) {
        return Z_STREAM_ERROR;
    }
    s = (deflate_state *) ZALLOC(strm, 1, sizeof(deflate_state));
    if (s == Z_NULL) return Z_MEM_ERROR;
    strm->state = (struct internal_state FAR *)s;
    s->strm = strm;

    s->noheader = noheader;
    s->w_bits = windowBits;
    s->w_size = 1 << s->w_bits;
    s->w_mask = s->w_size - 1;

    s->hash_bits = memLevel + 7;
    s->hash_size = 1 << s->hash_bits;
    s->hash_mask = s->hash_size - 1;
    s->hash_shift =  ((s->hash_bits+MIN_MATCH-1)/MIN_MATCH);

    s->window = (Bytef *) ZALLOC(strm, s->w_size, 2*sizeof(Byte));
    s->prev   = (Posf *)  ZALLOC(strm, s->w_size, sizeof(Pos));
    s->head   = (Posf *)  ZALLOC(strm, s->hash_size, sizeof(Pos));

    s->lit_bufsize = 1 << (memLevel + 6); /* 16K elements by default */

    s->pending_buf = (uchf *) ZALLOC(strm, s->lit_bufsize, 2*sizeof(ush));

    if (s->window == Z_NULL || s->prev == Z_NULL || s->head == Z_NULL ||
        s->pending_buf == Z_NULL) {
        strm->msg = z_errmsg[1-Z_MEM_ERROR];
        deflateEnd (strm);
        return Z_MEM_ERROR;
    }
    s->d_buf = (ushf *) &(s->pending_buf[s->lit_bufsize]);
    s->l_buf = (uchf *) &(s->pending_buf[3*s->lit_bufsize]);
    /* We overlay pending_buf and d_buf+l_buf. This works since the average
     * output size for (length,distance) codes is <= 32 bits (worst case
     * is 15+15+13=33).
     */

    s->level = level;
    s->strategy = strategy;
    s->method = (Byte)method;
    s->minCompr = minCompression;
    s->blocks_in_packet = 0;

    return deflateReset(strm);
}

/* ========================================================================= */
int deflateReset (strm)
    z_stream *strm;
{
    deflate_state *s;
    
    if (strm == Z_NULL || strm->state == Z_NULL ||
        strm->zalloc == Z_NULL || strm->zfree == Z_NULL) return Z_STREAM_ERROR;

    strm->total_in = strm->total_out = 0;
    strm->msg = Z_NULL; /* use zfree if we ever allocate msg dynamically */
    strm->data_type = Z_UNKNOWN;

    s = (deflate_state *)strm->state;
    s->pending = 0;
    s->pending_out = s->pending_buf;

    if (s->noheader < 0) {
        s->noheader = 0; /* was set to -1 by deflate(..., Z_FINISH); */
    }
    s->status = s->noheader ? BUSY_STATE : INIT_STATE;
    s->adler = 1;

    ct_init(s);
    lm_init(s);

    return Z_OK;
}

/* =========================================================================
 * Put a short in the pending buffer. The 16-bit value is put in MSB order.
 * IN assertion: the stream state is correct and there is enough room in
 * pending_buf.
 */
local void putShortMSB (s, b)
    deflate_state *s;
    uInt b;
{
    put_byte(s, (Byte)(b >> 8));
    put_byte(s, (Byte)(b & 0xff));
}   

/* =========================================================================
 * Flush as much pending output as possible.
 */
local void flush_pending(strm)
    z_stream *strm;
{
    deflate_state *state = (deflate_state *) strm->state;
    unsigned len = state->pending;

    if (len > strm->avail_out) len = strm->avail_out;
    if (len == 0) return;

    if (strm->next_out != NULL) {
	zmemcpy(strm->next_out, state->pending_out, len);
	strm->next_out += len;
    }
    state->pending_out += len;
    strm->total_out += len;
    strm->avail_out -= len;
    state->pending -= len;
    if (state->pending == 0) {
        state->pending_out = state->pending_buf;
    }
}

/* ========================================================================= */
int deflate (strm, flush)
    z_stream *strm;
    int flush;
{
    deflate_state *state = (deflate_state *) strm->state;

    if (strm == Z_NULL || state == Z_NULL) return Z_STREAM_ERROR;