/* trees.c -- output deflated data using Huffman coding
 * Copyright (C) 1995-2012 Jean-loup Gailly
 * detect_data_type() function provided freely by Cosmin Truta, 2006
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/*
 *  ALGORITHM
 *
 *      The "deflation" process uses several Huffman trees. The more
 *      common source values are represented by shorter bit sequences.
 *
 *      Each code tree is stored 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 inflate process, as described
 * in the deflate specification.
 *
 *  REFERENCES
 *
 *      Deutsch, L.P.,"'Deflate' Compressed Data Format Specification".
 *      Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc
 *
 *      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.
 */

/* @(#) $Id$ */

/* #define GEN_TREES_H */

#include "deflate.h"

#ifdef DEBUG
#include <ctype.h>
#endif

/* ===========================================================================
 * Constants
 */

#define MAX_BL_BITS 7
/* Bit length codes must not exceed MAX_BL_BITS bits */

#define END_BLOCK 256
/* end of block literal code */

#define REP_3_6 16
/* repeat previous bit length 3-6 times (2 bits of repeat count) */

#define REPZ_3_10 17
/* repeat a zero length 3-10 times  (3 bits of repeat count) */

#define REPZ_11_138 18
/* repeat a zero length 11-138 times  (7 bits of repeat count) */

local const int extra_lbits[LENGTH_CODES] /* 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};

local const int extra_dbits[D_CODES] /* 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};

local const int extra_blbits[BL_CODES] /* 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};

local const uch bl_order[BL_CODES] = {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.
 */

/* ===========================================================================
 * Local data. These are initialized only once.
 */

#define DIST_CODE_LEN 512 /* see definition of array dist_code below */

#if defined(GEN_TREES_H) || !defined(STDC)
/* non ANSI compilers may not accept trees.h */

local ct_data static_ltree[L_CODES + 2];
/* The static literal tree. Since the bit lengths are imposed, there is no
 * need for the L_CODES extra codes used during heap construction. However
 * The codes 286 and 287 are needed to build a canonical tree (see _tr_init
 * below).
 */

local ct_data static_dtree[D_CODES];
/* The static distance tree. (Actually a trivial tree since all codes use
 * 5 bits.)
 */

uch _dist_code[DIST_CODE_LEN];
/* Distance codes. The first 256 values correspond to the distances
 * 3 .. 258, the last 256 values correspond to the top 8 bits of
 * the 15 bit distances.
 */

uch _length_code[MAX_MATCH - MIN_MATCH + 1];
/* length code for each normalized match length (0 == MIN_MATCH) */

local int base_length[LENGTH_CODES];
/* First normalized length for each code (0 = MIN_MATCH) */

local int base_dist[D_CODES];
/* First normalized distance for each code (0 = distance of 1) */

#else
#include "trees.h"
#endif /* GEN_TREES_H */

struct static_tree_desc_s
{
	const ct_data *static_tree; /* static tree or NULL */
	const intf *extra_bits;     /* extra bits for each code or NULL */
	int extra_base;             /* base index for extra_bits */
	int elems;                  /* max number of elements in the tree */
	int max_length;             /* max bit length for the codes */
};

local static_tree_desc static_l_desc =
	{static_ltree, extra_lbits, LITERALS + 1, L_CODES, MAX_BITS};

local static_tree_desc static_d_desc =
	{static_dtree, extra_dbits, 0, D_CODES, MAX_BITS};

local static_tree_desc static_bl_desc =
	{(const ct_data *)0, extra_blbits, 0, BL_CODES, MAX_BL_BITS};

/* ===========================================================================
 * Local (static) routines in this file.
 */

local void tr_static_init OF((void));
local void init_block OF((deflate_state * s));
local void pqdownheap OF((deflate_state * s, ct_data *tree, int k));
local void gen_bitlen OF((deflate_state * s, tree_desc *desc));
local void gen_codes OF((ct_data * tree, int max_code, ushf *bl_count));
local void build_tree OF((deflate_state * s, tree_desc *desc));
local void scan_tree OF((deflate_state * s, ct_data *tree, int max_code));
local void send_tree OF((deflate_state * s, ct_data *tree, int max_code));
local int build_bl_tree OF((deflate_state * s));
local void send_all_trees OF((deflate_state * s, int lcodes, int dcodes,
							  int blcodes));
local void compress_block OF((deflate_state * s, const ct_data *ltree,
							  const ct_data *dtree));
local int detect_data_type OF((deflate_state * s));
local unsigned bi_reverse OF((unsigned value, int length));
local void bi_windup OF((deflate_state * s));
local void bi_flush OF((deflate_state * s));
local void copy_block OF((deflate_state * s, charf *buf, unsigned len,
						  int header));

#ifdef GEN_TREES_H
local void gen_trees_header OF((void));
#endif

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

#else /* DEBUG */
#define send_code(s, c, tree)                                 \
	{                                                         \
		if (z_verbose > 2) fprintf(stderr, "\ncd %3d ", (c)); \
		send_bits(s, tree[c].Code, tree[c].Len);              \
	}
#endif

/* ===========================================================================
 * Output a short LSB first on the stream.
 * IN assertion: there is enough room in pendingBuf.
 */
#define put_short(s, w)                    \
	{                                      \
		put_byte(s, (uch)((w)&0xff));      \
		put_byte(s, (uch)((ush)(w) >> 8)); \
	}

/* ===========================================================================
 * Send a value on a given number of bits.
 * IN assertion: length <= 16 and value fits in length bits.
 */
#ifdef DEBUG
local void send_bits OF((deflate_state * s, int value, int length));

local void send_bits(s, value, length)
	deflate_state *s;
int value;  /* value to send */
int length; /* number of bits */
{
	Tracevv((stderr, " l %2d v %4x ", length, value));
	Assert(length > 0 && length <= 15, "invalid length");
	s->bits_sent += (ulg)length;

	/* If not enough room in bi_buf, use (valid) bits from bi_buf and
     * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
     * unused bits in value.
     */
	if (s->bi_valid > (int)Buf_size - length)
	{
		s->bi_buf |= (ush)value << s->bi_valid;
		put_short(s, s->bi_buf);
		s->bi_buf = (ush)value >> (Buf_size - s->bi_valid);
		s->bi_valid += length - Buf_size;
	}
	else
	{
		s->bi_buf |= (ush)value << s->bi_valid;
		s->bi_valid += length;
	}
}
#else /* !DEBUG */

#define send_bits(s, value, length)                           \
	{                                                         \
		int len = length;                                     \
		if (s->bi_valid > (int)Buf_size - len)                \
		{                                                     \
			int val = value;                                  \
			s->bi_buf |= (ush)val << s->bi_valid;             \
			put_short(s, s->bi_buf);                          \
			s->bi_buf = (ush)val >> (Buf_size - s->bi_valid); \
			s->bi_valid += len - Buf_size;                    \
		}                                                     \
		else                                                  \
		{                                                     \
			s->bi_buf |= (ush)(value) << s->bi_valid;         \
			s->bi_valid += len;                               \
		}                                                     \
	}
#endif /* DEBUG */

/* the arguments must not have side effects */

/* ===========================================================================
 * Initialize the various 'constant' tables.
 */
local void tr_static_init()
{
#if defined(GEN_TREES_H) || !defined(STDC)
	static int static_init_done = 0;
	int n;      /* iterates over tree elements */
	int bits;   /* bit counter */
	int length; /* length value */
	int code;   /* code value */
	int dist;   /* distance index */
	ush bl_count[MAX_BITS + 1];
	/* number of codes at each bit length for an optimal tree */

	if (static_init_done) return;

		/* For some embedded targets, global variables are not initialized: */
#ifdef NO_INIT_GLOBAL_POINTERS
	static_l_desc.static_tree = static_ltree;
	static_l_desc.extra_bits = extra_lbits;
	static_d_desc.static_tree = static_dtree;
	static_d_desc.extra_bits = extra_dbits;
	static_bl_desc.extra_bits = extra_blbits;
#endif

	/* 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++] = (uch)code;
		}
	}
	Assert(length == 256, "tr_static_init: 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] = (uch)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++] = (uch)code;
		}
	}
	Assert(dist == 256, "tr_static_init: 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++] = (uch)code;
		}
	}
	Assert(dist == 256, "tr_static_init: 256+dist != 512");

	/* 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((ct_data *)static_ltree, L_CODES + 1, bl_count);

	/* The static distance tree is trivial: */
	for (n = 0; n < D_CODES; n++)
	{
		static_dtree[n].Len = 5;
		static_dtree[n].Code = bi_reverse((unsigned)n, 5);
	}
	static_init_done = 1;

#ifdef GEN_TREES_H
	gen_trees_header();
#endif
#endif /* defined(GEN_TREES_H) || !defined(STDC) */
}

/* ===========================================================================
 * Genererate the file trees.h describing the static trees.
 */
#ifdef GEN_TREES_H
#ifndef DEBUG
#include <stdio.h>
#endif

#define SEPARATOR(i, last, width) \
	((i) == (last) ? "\n};\n\n" : ((i) % (width) == (width)-1 ? ",\n" : ", "))

void gen_trees_header()
{
	FILE *header = fopen("trees.h", "w");
	int i;

	Assert(header != NULL, "Can't open trees.h");
	fprintf(header,
			"/* header created automatically with -DGEN_TREES_H */\n\n");

	fprintf(header, "local const ct_data static_ltree[L_CODES+2] = {\n");
	for (i = 0; i < L_CODES + 2; i++)
	{
		fprintf(header, "{{%3u},{%3u}}%s", static_ltree[i].Code,
				static_ltree[i].Len, SEPARATOR(i, L_CODES + 1, 5));
	}

	fprintf(header, "local const ct_data static_dtree[D_CODES] = {\n");
	for (i = 0; i < D_CODES; i++)
	{
		fprintf(header, "{{%2u},{%2u}}%s", static_dtree[i].Code,
				static_dtree[i].Len, SEPARATOR(i, D_CODES - 1, 5));
	}

	fprintf(header, "const uch ZLIB_INTERNAL _dist_code[DIST_CODE_LEN] = {\n");
	for (i = 0; i < DIST_CODE_LEN; i++)
	{
		fprintf(header, "%2u%s", _dist_code[i],
				SEPARATOR(i, DIST_CODE_LEN - 1, 20));
	}

	fprintf(header,
			"const uch ZLIB_INTERNAL _length_code[MAX_MATCH-MIN_MATCH+1]= {\n");
	for (i = 0; i < MAX_MATCH - MIN_MATCH + 1; i++)
	{
		fprintf(header, "%2u%s", _length_code[i],
				SEPARATOR(i, MAX_MATCH - MIN_MATCH, 20));
	}

	fprintf(header, "local const int base_length[LENGTH_CODES] = {\n");
	for (i = 0; i < LENGTH_CODES; i++)
	{
		fprintf(header, "%1u%s", base_length[i],
				SEPARATOR(i, LENGTH_CODES - 1, 20));
	}

	fprintf(header, "local const int base_dist[D_CODES] = {\n");
	for (i = 0; i < D_CODES; i++)
	{
		fprintf(header, "%5u%s", base_dist[i],
				SEPARATOR(i, D_CODES - 1, 10));
	}

	fclose(header);
}
#endif /* GEN_TREES_H */

/* ===========================================================================
 * Initialize the tree data structures for a new zlib stream.
 */
void ZLIB_INTERNAL _tr_init(s)
	deflate_state *s;
{
	tr_static_init();

	s->l_desc.dyn_tree = s->dyn_ltree;
	s->l_desc.stat_desc = &static_l_desc;

	s->d_desc.dyn_tree = s->dyn_dtree;
	s->d_desc.stat_desc = &static_d_desc;

	s->bl_desc.dyn_tree = s->bl_tree;
	s->bl_desc.stat_desc = &static_bl_desc;

	s->bi_buf = 0;
	s->bi_valid = 0;
#ifdef DEBUG
	s->compressed_len = 0L;
	s->bits_sent = 0L;
#endif

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

/* ===========================================================================
 * Initialize a new block.
 */
local void init_block(s)
	deflate_state *s;
{
	int n; /* iterates over tree elements */

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

	s->dyn_ltree[END_BLOCK].Freq = 1;
	s->opt_len = s->static_len = 0L;
	s->last_lit = s->matches = 0;
}

#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(s, tree, top)                      \
	{                                               \
		top = s->heap[SMALLEST];                    \
		s->heap[SMALLEST] = s->heap[s->heap_len--]; \
		pqdownheap(s, 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, depth)  \
	(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).
 */
local void pqdownheap(s, tree, k)
	deflate_state *s;
ct_data *tree; /* the tree to restore */
int k;         /* node to move down */
{
	int v = s->heap[k];
	int j = k << 1; /* left son of k */
	while (j <= s->heap_len)
	{
		/* Set j to the smallest of the two sons: */
		if (j < s->heap_len &&
			smaller(tree, s->heap[j + 1], s->heap[j], s->depth))
		{
			j++;
		}
		/* Exit if v is smaller than both sons */
		if (smaller(tree, v, s->heap[j], s->depth)) break;

		/* Exchange v with the smallest son */
		s->heap[k] = s->heap[j];
		k = j;

		/* And continue down the tree, setting j to the left son of k */
		j <<= 1;
	}
	s->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.
 */
local void gen_bitlen(s, desc)
	deflate_state *s;
tree_desc *desc; /* the tree descriptor */
{
	ct_data *tree = desc->dyn_tree;
	int max_code = desc->max_code;
	const ct_data *stree = desc->stat_desc->static_tree;
	const intf *extra = desc->stat_desc->extra_bits;
	int base = desc->stat_desc->extra_base;
	int max_length = desc->stat_desc->max_length;
	int h;            /* heap index */
	int n, m;         /* iterate over the tree elements */
	int bits;         /* bit length */
	int xbits;        /* extra bits */
	ush f;            /* frequency */
	int overflow = 0; /* number of elements with bit length too large */

	for (bits = 0; bits <= MAX_BITS; bits++) s->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[s->heap[s->heap_max]].Len = 0; /* root of the heap */

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

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

		s->bl_count[bits]++;
		xbits = 0;
		if (n >= base) xbits = extra[n - base];
		f = tree[n].Freq;
		s->opt_len += (ulg)f * (bits + xbits);
		if (stree) s->static_len += (ulg)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 (s->bl_count[bits] == 0) bits--;
		s->bl_count[bits]--;        /* move one leaf down the tree */
		s->bl_count[bits + 1] += 2; /* move one overflow item as its brother */
		s->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 = s->bl_count[bits];
		while (n != 0)
		{
			m = s->heap[--h];
			if (m > max_code) continue;
			if ((unsigned)tree[m].Len != (unsigned)bits)
			{
				Trace((stderr, "code %d bits %d->%d\n", m, tree[m].Len, bits));
				s->opt_len += ((long)bits - (long)tree[m].Len) * (long)tree[m].Freq;
				tree[m].Len = (ush)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.
 */
local void gen_codes(tree, max_code, bl_count)
	ct_data *tree; /* the tree to decorate */
int max_code;      /* largest code with non zero frequency */
ushf *bl_count;    /* number of codes at each bit length */
{
	ush next_code[MAX_BITS + 1]; /* next code value for each bit length */
	ush 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,
		   "inconsistent bit counts");
	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 = bi_reverse(next_code[len]++, len);

		Tracecv(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.
 */
local void build_tree(s, desc)
	deflate_state *s;
tree_desc *desc; /* the tree descriptor */
{
	ct_data *tree = desc->dyn_tree;
	const ct_data *stree = desc->stat_desc->static_tree;
	int elems = desc->stat_desc->elems;
	int n, m;          /* iterate over heap elements */
	int max_code = -1; /* largest code with non zero frequency */
	int node;          /* new node being created */

	/* 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.
     */
	s->heap_len = 0, s->heap_max = HEAP_SIZE;

	for (n = 0; n < elems; n++)
	{
		if (tree[n].Freq != 0)
		{
			s->heap[++(s->heap_len)] = max_code = n;
			s->depth[n] = 0;
		}
		else
		{
			tree[n].Len = 0;
		}
	}

	/* The pkzip format requires that at least one distance code exists,
     * and that at least one bit should be sent even if there is only one
     * possible code. So to avoid special checks later on we force at least
     * two codes of non zero frequency.
     */
	while (s->heap_len < 2)
	{
		node = s->heap[++(s->heap_len)] = (max_code < 2 ? ++max_code : 0);
		tree[node].Freq = 1;
		s->depth[node] = 0;
		s->opt_len--;
		if (stree) s->static_len -= stree[node].Len;
		/* node is 0 or 1 so it does not have extra bits */
	}
	desc->max_code = max_code;

	/* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
     * establish sub-heaps of increasing lengths:
     */
	for (n = s->heap_len / 2; n >= 1; n--) pqdownheap(s, tree, n);

	/* Construct the Huffman tree by repeatedly combining the least two
     * frequent nodes.
     */
	node = elems; /* next internal node of the tree */
	do
	{
		pqremove(s, tree, n);  /* n = node of least frequency */
		m = s->heap[SMALLEST]; /* m = node of next least frequency */

		s->heap[--(s->heap_max)] = n; /* keep the nodes sorted by frequency */
		s->heap[--(s->heap_max)] = m;

		/* Create a new node father of n and m */
		tree[node].Freq = tree[n].Freq + tree[m].Freq;
		s->depth[node] = (uch)((s->depth[n] >= s->depth[m] ? s->depth[n] : s->depth[m]) + 1);
		tree[n].Dad = tree[m].Dad = (ush)node;
#ifdef DUMP_BL_TREE
		if (tree == s->bl_tree)
		{
			fprintf(stderr, "\nnode %d(%d), sons %d(%d) %d(%d)",
					node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);
		}
#endif
		/* and insert the new node in the heap */
		s->heap[SMALLEST] = node++;
		pqdownheap(s, tree, SMALLEST);

	} while (s->heap_len >= 2);

	s->heap[--(s->heap_max)] = s->heap[SMALLEST];

	/* At this point, the fields freq and dad are set. We can now
     * generate the bit lengths.
     */
	gen_bitlen(s, (tree_desc *)desc);

	/* The field len is now set, we can generate the bit codes */
	gen_codes((ct_data *)tree, max_code, s->bl_count);
}

/* ===========================================================================
 * Scan a literal or distance tree to determine the frequencies of the codes
 * in the bit length tree.
 */
local void scan_tree(s, tree, max_code)
	deflate_state *s;
ct_data *tree; /* the tree to be scanned */
int max_code;  /* and its largest code of non zero frequency */
{
	int n;                     /* iterates over all tree elements */
	int prevlen = -1;          /* last emitted length */
	int curlen;                /* length of current code */
	int nextlen = tree[0].Len; /* length of next code */
	int count = 0;             /* repeat count of the current code */
	int max_count = 7;         /* max repeat count */
	int min_count = 4;         /* min repeat count */

	if (nextlen == 0) max_count = 138, min_count = 3;
	tree[max_code + 1].Len = (ush)0xffff; /* guard */

	for (n = 0; n <= max_code; n++)
	{
		curlen = nextlen;
		nextlen = tree[n + 1].Len;
		if (++count < max_count && curlen == nextlen)
		{
			continue;
		}
		else if (count < min_count)
		{
			s->bl_tree[curlen].Freq += count;
		}
		else if (curlen != 0)
		{
			if (curlen != prevlen) s->bl_tree[curlen].Freq++;
			s->bl_tree[REP_3_6].Freq++;
		}
		else if (count <= 10)
		{
			s->bl_tree[REPZ_3_10].Freq++;
		}
		else
		{
			s->bl_tree[REPZ_11_138].Freq++;
		}
		count = 0;
		prevlen = curlen;
		if (nextlen == 0)
		{
			max_count = 138, min_count = 3;
		}
		else if (curlen == nextlen)
		{
			max_count = 6, min_count = 3;
		}
		else
		{
			max_count = 7, min_count = 4;
		}
	}
}

/* ===========================================================================
 * Send a literal or distance tree in compressed form, using the codes in
 * bl_tree.
 */
local void send_tree(s, tree, max_code)
	deflate_state *s;
ct_data *tree; /* the tree to be scanned */
int max_code;  /* and its largest code of non zero frequency */
{
	int n;                     /* iterates over all tree elements */
	int prevlen = -1;          /* last emitted length */
	int curlen;                /* length of current code */
	int nextlen = tree[0].Len; /* length of next code */
	int count = 0;             /* repeat count of the current code */
	int max_count = 7;         /* max repeat count */
	int min_count = 4;         /* min repeat count */

	/* tree[max_code+1].Len = -1; */ /* guard already set */
	if (nextlen == 0) max_count = 138, min_count = 3;

	for (n = 0; n <= max_code; n++)
	{
		curlen = nextlen;
		nextlen = tree[n + 1].Len;
		if (++count < max_count && curlen == nextlen)
		{
			continue;
		}
		else if (count < min_count)
		{
			do
			{
				send_code(s, curlen, s->bl_tree);
			} while (--count != 0);
		}
		else if (curlen != 0)
		{
			if (curlen != prevlen)
			{
				send_code(s, curlen, s->bl_tree);
				count--;
			}
			Assert(count >= 3 && count <= 6, " 3_6?");
			send_code(s, REP_3_6, s->bl_tree);
			send_bits(s, count - 3, 2);
		}
		else if (count <= 10)
		{
			send_code(s, REPZ_3_10, s->bl_tree);
			send_bits(s, count - 3, 3);
		}
		else
		{
			send_code(s, REPZ_11_138, s->bl_tree);
			send_bits(s, count - 11, 7);
		}
		count = 0;
		prevlen = curlen;
		if (nextlen == 0)
		{
			max_count = 138, min_count = 3;
		}
		else if (curlen == nextlen)
		{
			max_count = 6, min_count = 3;
		}
		else
		{
			max_count = 7, min_count = 4;
		}
	}
}

/* ===========================================================================
 * Construct the Huffman tree for the bit lengths and return the index in
 * bl_order of the last bit length code to send.
 */
local int build_bl_tree(s)
	deflate_state *s;
{
	int max_blindex; /* index of last bit length code of non zero freq */

	/* Determine the bit length frequencies for literal and distance trees */
	scan_tree(s, (ct_data *)s->dyn_ltree, s->l_desc.max_code);
	scan_tree(s, (ct_data *)s->dyn_dtree, s->d_desc.max_code);

	/* Build the bit length tree: */
	build_tree(s, (tree_desc *)(&(s->bl_desc)));
	/* opt_len now includes the length of the tree representations, except
     * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
     */

	/* Determine the number of bit length codes to send. The pkzip format
     * requires that at least 4 bit length codes be sent. (appnote.txt says
     * 3 but the actual value used is 4.)
     */
	for (max_blindex = BL_CODES - 1; max_blindex >= 3; max_blindex--)
	{
		if (s->bl_tree[bl_order[max_blindex]].Len != 0) break;
	}
	/* Update opt_len to include the bit length tree and counts */
	s->opt_len += 3 * (max_blindex + 1) + 5 + 5 + 4;
	Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",
			s->opt_len, s->static_len));

	return max_blindex;
}

/* ===========================================================================
 * Send the header for a block using dynamic Huffman trees: the counts, the
 * lengths of the bit length codes, the literal tree and the distance tree.
 * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
 */
local void send_all_trees(s, lcodes, dcodes, blcodes)
	deflate_state *s;
int lcodes, dcodes, blcodes; /* number of codes for each tree */
{
	int rank; /* index in bl_order */

	Assert(lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");
	Assert(lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
		   "too many codes");
	Tracev((stderr, "\nbl counts: "));
	send_bits(s, lcodes - 257, 5); /* not +255 as stated in appnote.txt */
	send_bits(s, dcodes - 1, 5);
	send_bits(s, blcodes - 4, 4); /* not -3 as stated in appnote.txt */
	for (rank = 0; rank < blcodes; rank++)
	{
		Tracev((stderr, "\nbl code %2d ", bl_order[rank]));
		send_bits(s, s->bl_tree[bl_order[rank]].Len, 3);
	}
	Tracev((stderr, "\nbl tree: sent %ld", s->bits_sent));

	send_tree(s, (ct_data *)s->dyn_ltree, lcodes - 1); /* literal tree */
	Tracev((stderr, "\nlit tree: sent %ld", s->bits_sent));

	send_tree(s, (ct_data *)s->dyn_dtree, dcodes - 1); /* distance tree */
	Tracev((stderr, "\ndist tree: sent %ld", s->bits_sent));
}

/* ===========================================================================
 * Send a stored block
 */
void ZLIB_INTERNAL _tr_stored_block(s, buf, stored_len, last)
	deflate_state *s;
charf *buf;     /* input block */
ulg stored_len; /* length of input block */
int last;       /* one if this is the last block for a file */
{
	send_bits(s, (STORED_BLOCK << 1) + last, 3); /* send block type */
#ifdef DEBUG
	s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;
	s->compressed_len += (stored_len + 4) << 3;
#endif
	copy_block(s, buf, (unsigned)stored_len, 1); /* with header */
}

/* ===========================================================================
 * Flush the bits in the bit buffer to pending output (leaves at most 7 bits)
 */
void ZLIB_INTERNAL _tr_flush_bits(s)
	deflate_state *s;
{
	bi_flush(s);
}

/* ===========================================================================
 * Send one empty static block to give enough lookahead for inflate.
 * This takes 10 bits, of which 7 may remain in the bit buffer.
 */
void ZLIB_INTERNAL _tr_align(s)
	deflate_state *s;
{
	send_bits(s, STATIC_TREES << 1, 3);
	send_code(s, END_BLOCK, static_ltree);
#ifdef DEBUG
	s->compressed_len += 10L; /* 3 for block type, 7 for EOB */
#endif
	bi_flush(s);
}

/* ===========================================================================
 * Determine the best encoding for the current block: dynamic trees, static
 * trees or store, and output the encoded block to the zip file.
 */
void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)
	deflate_state *s;
charf *buf;     /* input block, or NULL if too old */
ulg stored_len; /* length of input block */
int last;       /* one if this is the last block for a file */
{
	ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
	int max_blindex = 0;       /* index of last bit length code of non zero freq */

	/* Build the Huffman trees unless a stored block is forced */
	if (s->level > 0)
	{
		/* Check if the file is binary or text */
		if (s->strm->data_type == Z_UNKNOWN)
			s->strm->data_type = detect_data_type(s);

		/* Construct the literal and distance trees */
		build_tree(s, (tree_desc *)(&(s->l_desc)));
		Tracev((stderr, "\nlit data: dyn %ld, stat %ld", s->opt_len,
				s->static_len));

		build_tree(s, (tree_desc *)(&(s->d_desc)));
		Tracev((stderr, "\ndist data: dyn %ld, stat %ld", s->opt_len,
				s->static_len));
		/* At this point, opt_len and static_len are the total bit lengths of
         * the compressed block data, excluding the tree representations.
         */

		/* Build the bit length tree for the above two trees, and get the index
         * in bl_order of the last bit length code to send.
         */
		max_blindex = build_bl_tree(s);

		/* Determine the best encoding. Compute the block lengths in bytes. */
		opt_lenb = (s->opt_len + 3 + 7) >> 3;
		static_lenb = (s->static_len + 3 + 7) >> 3;

		Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",
				opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,
				s->last_lit));

		if (static_lenb <= opt_lenb) opt_lenb = static_lenb;
	}
	else
	{
		Assert(buf != (char *)0, "lost buf");
		opt_lenb = static_lenb = stored_len + 5; /* force a stored block */
	}

#ifdef FORCE_STORED
	if (buf != (char *)0)
	{ /* force stored block */
#else
	if (stored_len + 4 <= opt_lenb && buf != (char *)0)
	{
		/* 4: two words for the lengths */
#endif
		/* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
         * Otherwise we can't have processed more than WSIZE input bytes since
         * the last block flush, because compression would have been
         * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
         * transform a block into a stored block.
         */
		_tr_stored_block(s, buf, stored_len, last);

#ifdef FORCE_STATIC
	}
	else if (static_lenb >= 0)
	{ /* force static trees */
#else
	}
	else if (s->strategy == Z_FIXED || static_lenb == opt_lenb)
	{
#endif
		send_bits(s, (STATIC_TREES << 1) + last, 3);
		compress_block(s, (const ct_data *)static_ltree,
					   (const ct_data *)static_dtree);
#ifdef DEBUG
		s->compressed_len += 3 + s->static_len;
#endif
	}
	else
	{
		send_bits(s, (DYN_TREES << 1) + last, 3);
		send_all_trees(s, s->l_desc.max_code + 1, s->d_desc.max_code + 1,
					   max_blindex + 1);
		compress_block(s, (const ct_data *)s->dyn_ltree,
					   (const ct_data *)s->dyn_dtree);
#ifdef DEBUG
		s->compressed_len += 3 + s->opt_len;
#endif
	}
	Assert(s->compressed_len == s->bits_sent, "bad compressed size");
	/* The above check is made mod 2^32, for files larger than 512 MB
     * and uLong implemented on 32 bits.
     */
	init_block(s);

	if (last)
	{
		bi_windup(s);
#ifdef DEBUG
		s->compressed_len += 7; /* align on byte boundary */
#endif
	}
	Tracev((stderr, "\ncomprlen %lu(%lu) ", s->compressed_len >> 3,
			s->compressed_len - 7 * last));
}

/* ===========================================================================
 * Save the match info and tally the frequency counts. Return true if
 * the current block must be flushed.
 */
int ZLIB_INTERNAL _tr_tally(s, dist, lc)
	deflate_state *s;
unsigned dist; /* distance of matched string */
unsigned lc;   /* match length-MIN_MATCH or unmatched char (if dist==0) */
{
	s->d_buf[s->last_lit] = (ush)dist;
	s->l_buf[s->last_lit++] = (uch)lc;
	if (dist == 0)
	{
		/* lc is the unmatched char */
		s->dyn_ltree[lc].Freq++;
	}
	else
	{
		s->matches++;
		/* Here, lc is the match length - MIN_MATCH */
		dist--; /* dist = match distance - 1 */
		Assert((ush)dist < (ush)MAX_DIST(s) &&
				   (ush)lc <= (ush)(MAX_MATCH - MIN_MATCH) &&
				   (ush)d_code(dist) < (ush)D_CODES,
			   "_tr_tally: bad match");

		s->dyn_ltree[_length_code[lc] + LITERALS + 1].Freq++;
		s->dyn_dtree[d_code(dist)].Freq++;
	}

#ifdef TRUNCATE_BLOCK
	/* Try to guess if it is profitable to stop the current block here */
	if ((s->last_lit & 0x1fff) == 0 && s->level > 2)
	{
		/* Compute an upper bound for the compressed length */
		ulg out_length = (ulg)s->last_lit * 8L;
		ulg in_length = (ulg)((long)s->strstart - s->block_start);
		int dcode;
		for (dcode = 0; dcode < D_CODES; dcode++)
		{
			out_length += (ulg)s->dyn_dtree[dcode].Freq *
						  (5L + extra_dbits[dcode]);
		}
		out_length >>= 3;
		Tracev((stderr, "\nlast_lit %u, in %ld, out ~%ld(%ld%%) ",
				s->last_lit, in_length, out_length,
				100L - out_length * 100L / in_length));
		if (s->matches < s->last_lit / 2 && out_length < in_length / 2) return 1;
	}
#endif
	return (s->last_lit == s->lit_bufsize - 1);
	/* We avoid equality with lit_bufsize because of wraparound at 64K
     * on 16 bit machines and because stored blocks are restricted to
     * 64K-1 bytes.
     */
}

/* ===========================================================================
 * Send the block data compressed using the given Huffman trees
 */
local void compress_block(s, ltree, dtree)
	deflate_state *s;
const ct_data *ltree; /* literal tree */
const ct_data *dtree; /* distance tree */
{
	unsigned dist;   /* distance of matched string */
	int lc;          /* match length or unmatched char (if dist == 0) */
	unsigned lx = 0; /* running index in l_buf */
	unsigned code;   /* the code to send */
	int extra;       /* number of extra bits to send */

	if (s->last_lit != 0) do
		{
			dist = s->d_buf[lx];
			lc = s->l_buf[lx++];
			if (dist == 0)
			{
				send_code(s, lc, ltree); /* send a literal byte */
				Tracecv(isgraph(lc), (stderr, " '%c' ", lc));
			}
			else
			{
				/* Here, lc is the match length - MIN_MATCH */
				code = _length_code[lc];
				send_code(s, code + LITERALS + 1, ltree); /* send the length code */
				extra = extra_lbits[code];
				if (extra != 0)
				{
					lc -= base_length[code];
					send_bits(s, lc, extra); /* send the extra length bits */
				}
				dist--; /* dist is now the match distance - 1 */
				code = d_code(dist);
				Assert(code < D_CODES, "bad d_code");

				send_code(s, code, dtree); /* send the distance code */
				extra = extra_dbits[code];
				if (extra != 0)
				{
					dist -= base_dist[code];
					send_bits(s, dist, extra); /* send the extra distance bits */
				}
			} /* literal or match pair ? */

			/* Check that the overlay between pending_buf and d_buf+l_buf is ok: */
			Assert((uInt)(s->pending) < s->lit_bufsize + 2 * lx,
				   "pendingBuf overflow");

		} while (lx < s->last_lit);

	send_code(s, END_BLOCK, ltree);
}

/* ===========================================================================
 * Check if the data type is TEXT or BINARY, using the following algorithm:
 * - TEXT if the two conditions below are satisfied:
 *    a) There are no non-portable control characters belonging to the
 *       "black list" (0..6, 14..25, 28..31).
 *    b) There is at least one printable character belonging to the
 *       "white list" (9 {TAB}, 10 {LF}, 13 {CR}, 32..255).
 * - BINARY otherwise.
 * - The following partially-portable control characters form a
 *   "gray list" that is ignored in this detection algorithm:
 *   (7 {BEL}, 8 {BS}, 11 {VT}, 12 {FF}, 26 {SUB}, 27 {ESC}).
 * IN assertion: the fields Freq of dyn_ltree are set.
 */
local int detect_data_type(s)
	deflate_state *s;
{
	/* black_mask is the bit mask of black-listed bytes
     * set bits 0..6, 14..25, and 28..31
     * 0xf3ffc07f = binary 11110011111111111100000001111111
     */
	unsigned long black_mask = 0xf3ffc07fUL;
	int n;

	/* Check for non-textual ("black-listed") bytes. */
	for (n = 0; n <= 31; n++, black_mask >>= 1)
		if ((black_mask & 1) && (s->dyn_ltree[n].Freq != 0))
			return Z_BINARY;

	/* Check for textual ("white-listed") bytes. */
	if (s->dyn_ltree[9].Freq != 0 || s->dyn_ltree[10].Freq != 0 || s->dyn_ltree[13].Freq != 0)
		return Z_TEXT;
	for (n = 32; n < LITERALS; n++)
		if (s->dyn_ltree[n].Freq != 0)
			return Z_TEXT;

	/* There are no "black-listed" or "white-listed" bytes:
     * this stream either is empty or has tolerated ("gray-listed") bytes only.
     */
	return Z_BINARY;
}

/* ===========================================================================
 * Reverse the first len bits of a code, using straightforward code (a faster
 * method would use a table)
 * IN assertion: 1 <= len <= 15
 */
local unsigned bi_reverse(code, len) unsigned code; /* the value to invert */
int len;                                            /* its bit length */
{
	register unsigned res = 0;
	do
	{
		res |= code & 1;
		code >>= 1, res <<= 1;
	} while (--len > 0);
	return res >> 1;
}

/* ===========================================================================
 * Flush the bit buffer, keeping at most 7 bits in it.
 */
local void bi_flush(s)
	deflate_state *s;
{
	if (s->bi_valid == 16)
	{
		put_short(s, s->bi_buf);
		s->bi_buf = 0;
		s->bi_valid = 0;
	}
	else if (s->bi_valid >= 8)
	{
		put_byte(s, (Byte)s->bi_buf);
		s->bi_buf >>= 8;
		s->bi_valid -= 8;
	}
}

/* ===========================================================================
 * Flush the bit buffer and align the output on a byte boundary
 */
local void bi_windup(s)
	deflate_state *s;
{
	if (s->bi_valid > 8)
	{
		put_short(s, s->bi_buf);
	}
	else if (s->bi_valid > 0)
	{
		put_byte(s, (Byte)s->bi_buf);
	}
	s->bi_buf = 0;
	s->bi_valid = 0;
#ifdef DEBUG
	s->bits_sent = (s->bits_sent + 7) & ~7;
#endif
}

/* ===========================================================================
 * Copy a stored block, storing first the length and its
 * one's complement if requested.
 */
local void copy_block(s, buf, len, header)
	deflate_state *s;
charf *buf;   /* the input data */
unsigned len; /* its length */
int header;   /* true if block header must be written */
{
	bi_windup(s); /* align on byte boundary */

	if (header)
	{
		put_short(s, (ush)len);
		put_short(s, (ush)~len);
#ifdef DEBUG
		s->bits_sent += 2 * 16;
#endif
	}
#ifdef DEBUG
	s->bits_sent += (ulg)len << 3;
#endif
	while (len--)
	{
		put_byte(s, *buf++);
	}
}