zdeflate.cpp

椭圆曲线密码系统教程和相关源代码,是非常难得的学术资料

// zdeflate.cpp - modified by Wei Dai from:
// Distributed with Jean-loup Gailly's permission.

/*
 The following sorce code is derived from Info-Zip 'zip' 2.01
 distribution copyrighted by Mark Adler, Richard B. Wales,
 Jean-loup Gailly, Kai Uwe Rommel, Igor Mandrichenko and John Bush.
*/

/*
 *  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
 */

#include "pch.h"
#include "zdeflate.h"
#include <stddef.h>     // for NULL

NAMESPACE_BEGIN(CryptoPP)

/* Define this symbol if your target allows access to unaligned data.
 * This is not mandatory, just a speed optimization. The compressed
 * output is strictly identical.
 */
#ifndef UNALIGNED_OK
#  ifdef MSDOS
#   ifndef WIN32
#    define UNALIGNED_OK
#   endif
#  endif
#  ifdef i386
#    define UNALIGNED_OK
#  endif
#  ifdef mc68020
#    define UNALIGNED_OK
#  endif
#  ifdef vax
#    define UNALIGNED_OK
#  endif
#endif

/* 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.
 */

#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 */

#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. */

/* 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. */

const Deflator::config Deflator::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. */

/* 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))

void Deflator::init_hash()
{
   register unsigned j;

   for (ins_h=0, 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. */
}

/* Initialize the "longest match" routines for a new file */
Deflator::Deflator(int deflate_level, BufferedTransformation *outQ)
	: Filter(outQ),
	  CodeTree(deflate_level, *outQueue),
	  window(WINDOW_SIZE), prev(WSIZE), head(HASH_SIZE)
{
   match_available = 0;
   match_length = MIN_MATCH-1;
   /* Initialize the hash table (avoiding 64K overflow for 16 bit systems).
	* prev[] will be initialized on the fly. */
	memset(head, NIL, HASH_SIZE*sizeof(*head.ptr));
   /* Set the default configuration parameters: */
   max_lazy_match   = configuration_table[deflate_level].max_lazy;
   good_match       = configuration_table[deflate_level].good_length;
   nice_match       = configuration_table[deflate_level].nice_length;
   max_chain_length = configuration_table[deflate_level].max_chain;

   strstart = 0;
   block_start = 0L;
   lookahead = 0;
   uptodate  = 0;
   minlookahead = MIN_LOOKAHEAD-1;
   match_available = 0;
   prev_length = MIN_MATCH-1;
}

void Deflator::Put(const byte *inString, unsigned int length)
{
	if (deflate_level <= 3)
		fast_deflate(inString, length);
	else
		lazy_deflate(inString, length);
}

void Deflator::InputFinished()
{
	minlookahead = 0;
	Put(NULL, 0);
}

/* 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.  A 68000 version is in amiga/match_68.a -- this could be used
 * with other 68000 based systems such as Macintosh with a little effort.
 */
int Deflator::longest_match(IPos cur_match)
{
   unsigned chain_length = max_chain_length;   /* max hash chain length */
   register byte *scan = window + strstart;     /* current string */
   register byte *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 byte *strend = window + strstart + MAX_MATCH - 1;
   register word16 scan_start = *(word16*)scan;
   register word16 scan_end   = *(word16*)(scan+best_len-1);
#else
   register byte *strend = window + strstart + MAX_MATCH;
   register byte scan_end1 = scan[best_len-1];
   register byte scan_end  = scan[best_len];
#endif

   /* Do not waste too much time if we already have a good match: */
   if (prev_length >= good_match) {
	   chain_length >>= 2;
   }
//   assert(strstart <= (unsigned)WINDOW_SIZE-MIN_LOOKAHEAD);

   do {
	   assert(cur_match < strstart);
	   match = window + cur_match;

	   /* Skip to next match if the match length cannot increase
		* or if the match length is less than 2:
		*/
#ifdef UNALIGNED_OK
	   /* This code assumes sizeof(unsigned short) == 2. Do not use
		* UNALIGNED_OK if your compiler uses a different size.
		*/
	   if (*(word16*)(match+best_len-1) != scan_end ||
		   *(word16*)match != scan_start) continue;

	   /* It is not necessary to compare scan[2] and match[2] since they are
		* always equal when the other bytes match, given that the hash keys
		* are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at
		* strstart+3, +5, ... up to strstart+257. We check for insufficient
		* lookahead only every 4th comparison; the 128th check will be made
		* at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is
		* necessary to put more guard bytes at the end of the window, or
		* to check more often for insufficient lookahead.
		*/
	   scan++, match++;
	   do {
	   } while (*(word16*)(scan+=2) == *(word16*)(match+=2) &&
				*(word16*)(scan+=2) == *(word16*)(match+=2) &&
				*(word16*)(scan+=2) == *(word16*)(match+=2) &&
				*(word16*)(scan+=2) == *(word16*)(match+=2) &&
				scan < strend);
	   /* The funny "do {}" generates better code on most compilers */

	   /* Here, scan <= window+strstart+257 */
	   assert(scan <= window+(unsigned)(WINDOW_SIZE-1));
	   if (*scan == *match) scan++;

	   len = (MAX_MATCH - 1) - (int)(strend-scan);
	   scan = strend - (MAX_MATCH-1);

#else /* UNALIGNED_OK */

	   if (match[best_len]   != scan_end  ||
		   match[best_len-1] != scan_end1 ||
		   *match            != *scan     ||
		   *++match          != scan[1])      continue;

	   /* The check at best_len-1 can be removed because it will be made
		* again later. (This heuristic is not always a win.)
		* It is not necessary to compare scan[2] and match[2] since they
		* are always equal when the other bytes match, given that
		* the hash keys are equal and that HASH_BITS >= 8.
		*/
	   scan += 2, match++;

	   /* We check for insufficient lookahead only every 8th comparison;
		* the 256th check will be made at strstart+258.
		*/
	   do {