/* deflate.c -- compress data using the deflation algorithm * Copyright (C) 1992-1993 Jean-loup Gailly * This is free software; you can redistribute it and/or modify it under the * terms of the GNU General Public License, see the file COPYING. *//* *  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 * *      void lm_init (int pack_level, ush *flags) *          Initialize the "longest match" routines for a new file * *      ulg deflate (void) *          Processes a new input file and return its compressed length. Sets *          the compressed length, crc, deflate flags and internal file *          attributes. */#include <stdio.h>#include "tailor.h"#include "gzip.h"#include "lzw.h" /* just for consistency checking */#ifdef RCSIDstatic char rcsid[] = "$Id: deflate.c,v 0.15 1993/06/24 10:53:53 jloup Exp $";#endif/* =========================================================================== * 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/* To save space (see unlzw.c), we overlay prev+head with tab_prefix and * window with tab_suffix. Check that we can do this: */#if (WSIZE<<1) > (1<<BITS)   error: cannot overlay window with tab_suffix and prev with tab_prefix0#endif#if HASH_BITS > BITS-1   error: cannot overlay head with tab_prefix1#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 */#define FAST 4#define SLOW 2/* speed options for the general purpose bit flag */#ifndef TOO_FAR#  define TOO_FAR 4096#endif/* Matches of length 3 are discarded if their distance exceeds TOO_FAR *//* =========================================================================== * Local data used by the "longest match" routines. */typedef ush Pos;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. *//* DECLARE(uch, 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). *//* DECLARE(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. *//* DECLARE(Pos, head, 1<<HASH_BITS); *//* Heads of the hash chains or NIL. */ulg window_size = (ulg)2*WSIZE;/* 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. */local unsigned ins_h;  /* hash index of string to be inserted */#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 */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 */local int           eofile;        /* flag set at end of input file */local unsigned      lookahead;     /* number of valid bytes ahead in window */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. */local 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. */local int compr_level;/* compression level (1..9) */unsigned near good_match;/* Use a faster search when the previous match is longer than this *//* 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 {   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;#ifdef  FULL_SEARCH# define nice_match MAX_MATCH#else  int near nice_match; /* Stop searching when current match exceeds this */#endiflocal 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((void));local ulg deflate_fast   OF((void));      int  longest_match OF((IPos cur_match));#ifdef ASMV      void match_init OF((void)); /* asm code initialization */#endif#ifdef DEBUGlocal  void check_match OF((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(s, match_head) \   (UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]), \    prev[(s) & WMASK] = match_head = head[ins_h], \    head[ins_h] = (s))/* =========================================================================== * Initialize the "longest match" routines for a new file */void lm_init (pack_level, flags)    int pack_level; /* 0: store, 1: best speed, 9: best compression */    ush *flags;     /* general purpose bit flag */{    register unsigned j;    if (pack_level < 1 || pack_level > 9) error("bad pack level");    compr_level = pack_level;    /* Initialize the hash table. */#if defined(MAXSEG_64K) && HASH_BITS == 15    for (j = 0;  j < HASH_SIZE; j++) head[j] = NIL;#else    memzero((char*)head, HASH_SIZE*sizeof(*head));#endif    /* prev will be initialized on the fly */    /* Set the default configuration parameters:     */    max_lazy_match   = configuration_table[pack_level].max_lazy;    good_match       = configuration_table[pack_level].good_length;#ifndef FULL_SEARCH    nice_match       = configuration_table[pack_level].nice_length;#endif    max_chain_length = configuration_table[pack_level].max_chain;    if (pack_level == 1) {       *flags |= FAST;    } else if (pack_level == 9) {       *flags |= SLOW;    }    /* ??? reduce max_chain_length for binary files */    strstart = 0;    block_start = 0L;#ifdef ASMV    match_init(); /* initialize the asm code */#endif    lookahead = read_buf((char*)window,			 sizeof(int) <= 2 ? (unsigned)WSIZE : 2*WSIZE);    if (lookahead == 0 || lookahead == (unsigned)EOF) {       eofile = 1, lookahead = 0;       return;    }    eofile = 0;    /* Make sure that we always have enough lookahead. This is important     * if input comes from a device such as a tty.     */    while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window();    ins_h = 0;    for (j=0; j<MIN_MATCH-1; j++) UPDATE_HASH(ins_h, window[j]);    /* If lookahead < MIN_MATCH, ins_h is garbage, but this is     * not important since only literal bytes will be emitted.     */}/* =========================================================================== * Set match_start to the longest match starting at the given string and * return its length. Matches shorter or equal to prev_length are discarded, * in which case the result is equal to prev_length and match_start is * garbage. * IN assertions: cur_match is the head of the hash chain for the current *   string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1 */#ifndef ASMV/* For MSDOS, OS/2 and 386 Unix, an optimized version is in match.asm or * match.s. The code is functionally equivalent, so you can use the C version * if desired. */int longest_match(cur_match)    IPos cur_match;                             /* current match */{    unsigned chain_length = max_chain_length;   /* max hash chain length */    register uch *scan = window + strstart;     /* current string */    register uch *match;                        /* matched string */    register int len;                           /* length of current match */    int best_len = prev_length;                 /* best match length so far */    IPos limit = strstart > (IPos)MAX_DIST ? strstart - (IPos)MAX_DIST : NIL;    /* Stop when cur_match becomes <= limit. To simplify the code,     * we prevent matches with the string of window index 0.     *//* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16. * It is easy to get rid of this optimization if necessary. */#if HASH_BITS < 8 || MAX_MATCH != 258   error: Code too clever#endif#ifdef UNALIGNED_OK    /* Compare two bytes at a time. Note: this is not always beneficial.     * Try with and without -DUNALIGNED_OK to check.     */    register uch *strend = window + strstart + MAX_MATCH - 1;    register ush scan_start = *(ush*)scan;