ztrees.cpp

300种加密解密算法

// ztrees.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.
*/

/*
 *  trees.c by Jean-loup Gailly
 *
 *  This is a new version of im_ctree.c originally written by Richard B. Wales
 *  for the defunct implosion method.
 *
 *  PURPOSE
 *
 *      Encode various sets of source values using variable-length
 *      binary code trees.
 *
 *  DISCUSSION
 *
 *      The PKZIP "deflation" process uses several Huffman trees. The more
 *      common source values are represented by shorter bit sequences.
 *
 *      Each code tree is stored in the ZIP file in a compressed form
 *      which is itself a Huffman encoding of the lengths of
 *      all the code strings (in ascending order by source values).
 *      The actual code strings are reconstructed from the lengths in
 *      the UNZIP process, as described in the "application note"
 *      (APPNOTE.TXT) distributed as part of PKWARE's PKZIP program.
 *
 *  REFERENCES
 *
 *      Lynch, Thomas J.
 *          Data Compression:  Techniques and Applications, pp. 53-55.
 *          Lifetime Learning Publications, 1985.  ISBN 0-534-03418-7.
 *
 *      Storer, James A.
 *          Data Compression:  Methods and Theory, pp. 49-50.
 *          Computer Science Press, 1988.  ISBN 0-7167-8156-5.
 *
 *      Sedgewick, R.
 *          Algorithms, p290.
 *          Addison-Wesley, 1983. ISBN 0-201-06672-6.
 *
 *  INTERFACE
 *
 *      int ct_init (void)
 *          Allocate the match buffer and initialize the various tables.
 *
 *      int ct_tally(int dist, int lc);
 *          Save the match info and tally the frequency counts.
 *          Return true if the current block must be flushed.
 *
 *      long flush_block (char *buf, ulg stored_len, int eof)
 *          Determine the best encoding for the current block: dynamic trees,
 *          static trees or store, and output the encoded block to the zip
 *          file. Returns the total compressed length for the file so far.
 */

#include "pch.h"
#include "ztrees.h"

NAMESPACE_BEGIN(CryptoPP)

bool CodeTree::streesBuilt = false;
CodeTree::ct_data CodeTree::static_ltree[CodeTree::L_CODES+2];
CodeTree::ct_data CodeTree::static_dtree[CodeTree::D_CODES];
                                            
const int CodeTree::extra_lbits[] /* extra bits for each length code */
   = {0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0};

const int CodeTree::extra_dbits[] /* extra bits for each distance code */
   = {0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13};

const int CodeTree::extra_blbits[]/* extra bits for each bit length code */
   = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};

const byte CodeTree::bl_order[]
   = {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};
/* The lengths of the bit length codes are sent in order of decreasing
 * probability, to avoid transmitting the lengths for unused bit length codes.
 */

#define send_code(c, tree) send_bits(tree[c].Code, tree[c].Len)
/* Send a code of the given tree. c and tree must not have side effects */

#define d_code(dist) \
   ((dist) < 256 ? dist_code[dist] : dist_code[256+((dist)>>7)])
/* Mapping from a distance to a distance code. dist is the distance - 1 and
 * must not have side effects. dist_code[256] and dist_code[257] are never
 * used.
 */

#define MAX(a,b) (a >= b ? a : b)
/* the arguments must not have side effects */

static unsigned reverse(unsigned int code, int len)
/* Reverse the first len bits of a code. */
{
   register unsigned res = 0;
   do res = (res << 1) | (code & 1), code>>=1; while (--len);
   return res;
}

/* Allocate the match buffer and initialize the various tables. */
CodeTree::CodeTree(int deflate_level, BufferedTransformation &outQ)
  : BitOutput(outQ),
	deflate_level(deflate_level),
	dyn_ltree(HEAP_SIZE), dyn_dtree(2*D_CODES+1),
	bl_tree(2*BL_CODES+1),
	bl_count(MAX_BITS+1),
	l_desc(dyn_ltree, static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS, 0),
	d_desc(dyn_dtree, static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS, 0),
	bl_desc(bl_tree, (ct_data *)0, extra_blbits, 0,     BL_CODES, MAX_BL_BITS, 0),
	heap(2*L_CODES+1),
	depth(2*L_CODES+1),
	length_code(MAX_MATCH-MIN_MATCH+1),
	dist_code(512),
	base_length(LENGTH_CODES),
	base_dist(D_CODES),
	l_buf(LIT_BUFSIZE),
	d_buf(DIST_BUFSIZE),
	flag_buf(LIT_BUFSIZE/8)
{

   unsigned int n;    /* iterates over tree elements */
   int bits;      /* bit counter */
   int length;    /* length value */
   register int code; /* code value */
   int dist;      /* distance index */

	compressed_len = input_len = 0L;

   /* Initialize the mapping length (0..255) -> length code (0..28) */
   length = 0;
   for (code=0; code < LENGTH_CODES-1; code++) {
	  base_length[code] = length;
	  for (n=0; n < (1<<extra_lbits[code]); n++) {
		 length_code[length++] = (byte)code;
	  }
   }
   assert (length == 256);
	/* Note that the length 255 (match length 258) can be represented
	   in two different ways: code 284 + 5 bits or code 285, so we
	   overwrite length_code[255] to use the best encoding:     */
   length_code[length-1] = (byte)code;

   /* Initialize the mapping dist (0..32K) -> dist code (0..29) */
   dist = 0;
   for (code=0 ; code < 16; code++) {
	  base_dist[code] = dist;
	  for (n=0; n < (1<<extra_dbits[code]); n++) {
		 dist_code[dist++] = (byte)code;
	  }
   }
   assert (dist == 256);
   dist >>= 7; /* from now on, all distances are divided by 128 */
   for (; code < D_CODES; code++) {
	  base_dist[code] = dist << 7;
	  for (n=0; n < (1<<(extra_dbits[code]-7)); n++) {
		 dist_code[256 + dist++] = (byte)code;
	  }
   }
   assert (dist == 256);

   if (!streesBuilt)
   {
	   /* Construct the codes of the static literal tree */
	   for (bits=0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;
	   n = 0;
	   while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;
	   while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;
	   while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;
	   while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;
	   /* Codes 286 and 287 do not exist, but we must include them in the tree
		  construction to get a canonical Huffman tree (longest code all ones) */
	   gen_codes(static_ltree, L_CODES+1);

	   /* The static distance tree is trivial: */
	   for (n=0; n < D_CODES; n++) {
		  static_dtree[n].Len = 5;
		  static_dtree[n].Code = reverse(n, 5);
	   }
	   streesBuilt = true;
   }

   /* Initialize the first block of the first file: */
   init_block();
}

/* Initialize a new block. */
void CodeTree::init_block()
{
   register int n; /* iterates over tree elements */

   /* Initialize the trees. */
   for (n=0; n < L_CODES;  n++) dyn_ltree[n].Freq = 0;
   for (n=0; n < D_CODES;  n++) dyn_dtree[n].Freq = 0;
   for (n=0; n < BL_CODES; n++) bl_tree[n].Freq = 0;

   dyn_ltree[END_BLOCK].Freq = 1;
   opt_len = static_len = 0L;
   last_lit = last_dist = last_flags = 0;
   flags = 0; flag_bit = 1;
}

#define SMALLEST 1
/* Index within the heap array of least frequent node in the Huffman tree */

/*
 * Remove the smallest element from the heap and recreate the heap with
 * one less element. Updates heap and heap_len.
 */
#define pqremove(tree, top) \
{\
	top = heap[SMALLEST]; \
	heap[SMALLEST] = heap[heap_len--]; \
	pqdownheap(tree, SMALLEST); \
}

/*
 * Compares to subtrees, using the tree depth as tie breaker when
 * the subtrees have equal frequency. This minimizes the worst case length.
 */
#define smaller(tree, n, m) \
   (tree[n].Freq < tree[m].Freq || \
   (tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))

/*
 * Restore the heap property by moving down the tree starting at node k,
 * exchanging a node with the smallest of its two sons if necessary, stopping
 * when the heap property is re-established (each father smaller than its
 * two sons).
 */
void CodeTree::pqdownheap(ct_data *tree, int k)
{
	int v = heap[k];
	int j = k << 1;  /* left son of k */
	int htemp;       /* required because of bug in SASC compiler */

	while (j <= heap_len) {
		/* Set j to the smallest of the two sons: */
		if (j < heap_len && smaller(tree, heap[j+1], heap[j])) j++;

		/* Exit if v is smaller than both sons */
		htemp = heap[j];
		if (smaller(tree, v, htemp)) break;

		/* Exchange v with the smallest son */
		heap[k] = htemp;
		k = j;

		/* And continue down the tree, setting j to the left son of k */
		j <<= 1;
	}
	heap[k] = v;
}

/*
 * Compute the optimal bit lengths for a tree and update the total bit length
 * for the current block.
 * IN assertion: the fields freq and dad are set, heap[heap_max] and
 *    above are the tree nodes sorted by increasing frequency.
 * OUT assertions: the field len is set to the optimal bit length, the
 *     array bl_count contains the frequencies for each bit length.
 *     The length opt_len is updated; static_len is also updated if stree is
 *     not null.
 */
void CodeTree::gen_bitlen(tree_desc *desc)
{
	ct_data *tree  = desc->dyn_tree;
	const int *extra     = desc->extra_bits;
	int base            = desc->extra_base;
	int max_code        = desc->max_code;
	int max_length      = desc->max_length;
	const ct_data *stree = desc->static_tree;
	int h;              /* heap index */
	int n, m;           /* iterate over the tree elements */
	int bits;           /* bit length */
	int xbits;          /* extra bits */
	word16 f;              /* frequency */
	int overflow = 0;   /* number of elements with bit length too large */

	for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;

	/* In a first pass, compute the optimal bit lengths (which may
	 * overflow in the case of the bit length tree).
	 */
	tree[heap[heap_max]].Len = 0; /* root of the heap */

	for (h = heap_max+1; h < HEAP_SIZE; h++) {
		n = heap[h];
		bits = tree[tree[n].Dad].Len + 1;
		if (bits > max_length) bits = max_length, overflow++;
		tree[n].Len = bits;
		/* We overwrite tree[n].Dad which is no longer needed */

		if (n > max_code) continue; /* not a leaf node */

		bl_count[bits]++;
		xbits = 0;
		if (n >= base) xbits = extra[n-base];
		f = tree[n].Freq;
		opt_len += (word32)f * (bits + xbits);
		if (stree) static_len += (word32)f * (stree[n].Len + xbits);
	}
	if (overflow == 0) return;

//    Trace((stderr,"\nbit length overflow\n"));
	/* This happens for example on obj2 and pic of the Calgary corpus */

	/* Find the first bit length which could increase: */
	do {
		bits = max_length-1;
		while (bl_count[bits] == 0) bits--;
		bl_count[bits]--;      /* move one leaf down the tree */
		bl_count[bits+1] += 2; /* move one overflow item as its brother */
		bl_count[max_length]--;
		/* The brother of the overflow item also moves one step up,
		 * but this does not affect bl_count[max_length]
		 */
		overflow -= 2;
	} while (overflow > 0);

	/* Now recompute all bit lengths, scanning in increasing frequency.
	 * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
	 * lengths instead of fixing only the wrong ones. This idea is taken
	 * from 'ar' written by Haruhiko Okumura.)
	 */
	for (bits = max_length; bits != 0; bits--) {
		n = bl_count[bits];
		while (n != 0) {
			m = heap[--h];
			if (m > max_code) continue;
			if (tree[m].Len != (unsigned) bits) {
//                Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
				opt_len += ((long)bits-(long)tree[m].Len)*(long)tree[m].Freq;
				tree[m].Len = bits;
			}
			n--;
		}
	}
}

/*
 * Generate the codes for a given tree and bit counts (which need not be
 * optimal).
 * IN assertion: the array bl_count contains the bit length statistics for
 * the given tree and the field len is set for all tree elements.
 * OUT assertion: the field code is set for all tree elements of non
 *     zero code length.
 */
void CodeTree::gen_codes (ct_data *tree, int max_code)
{
	word16 next_code[MAX_BITS+1]; /* next code value for each bit length */
	word16 code = 0;              /* running code value */
	int bits;                  /* bit index */
	int n;                     /* code index */

	/* The distribution counts are first used to generate the code values
	 * without bit reversal.
	 */
	for (bits = 1; bits <= MAX_BITS; bits++) {
		next_code[bits] = code = (code + bl_count[bits-1]) << 1;
	}
	/* Check that the bit counts in bl_count are consistent. The last code
	 * must be all ones.
	 */
	assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1);
//    Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

	for (n = 0;  n <= max_code; n++) {
		int len = tree[n].Len;
		if (len == 0) continue;
		/* Now reverse the bits */
		tree[n].Code = reverse(next_code[len]++, len);

//        Tracec(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",
//             n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));
	}
}

/*
 * Construct one Huffman tree and assigns the code bit strings and lengths.
 * Update the total bit length for the current block.
 * IN assertion: the field freq is set for all tree elements.
 * OUT assertions: the fields len and code are set to the optimal bit length
 *     and corresponding code. The length opt_len is updated; static_len is
 *     also updated if stree is not null. The field max_code is set.
 */
void CodeTree::build_tree(tree_desc *desc)
{
	ct_data *tree   = desc->dyn_tree;
	const ct_data *stree  = desc->static_tree;
	int elems            = desc->elems;
	int n, m;          /* iterate over heap elements */
	int max_code = -1; /* largest code with non zero frequency */
	int node = elems;  /* next internal node of the tree */

	/* Construct the initial heap, with least frequent element in
	 * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
	 * heap[0] is not used.
	 */
	heap_len = 0, heap_max = HEAP_SIZE;