FreeBSD/Linux Kernel Cross Reference
sys/libkern/zlib/trees.c

     /*
      * Copyright (c) 2008 Apple Inc. All rights reserved.
      *
      * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
      * 
      * This file contains Original Code and/or Modifications of Original Code
      * as defined in and that are subject to the Apple Public Source License
      * Version 2.0 (the 'License'). You may not use this file except in
      * compliance with the License. The rights granted to you under the License
     * may not be used to create, or enable the creation or redistribution of,
     * unlawful or unlicensed copies of an Apple operating system, or to
     * circumvent, violate, or enable the circumvention or violation of, any
     * terms of an Apple operating system software license agreement.
     * 
     * Please obtain a copy of the License at
     * http://www.opensource.apple.com/apsl/ and read it before using this file.
     * 
     * The Original Code and all software distributed under the License are
     * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
     * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
     * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
     * Please see the License for the specific language governing rights and
     * limitations under the License.
     * 
     * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
     */
    /* trees.c -- output deflated data using Huffman coding
     * Copyright (C) 1995-2005 Jean-loup Gailly
     * 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.
    */
   
   #define Buf_size (8 * 2*sizeof(char))
   /* Number of bits used within bi_buf. (bi_buf might be implemented on
    * more than 16 bits on some systems.)
    */
   
   /* ===========================================================================
    * 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, ct_data *ltree,
                                 ct_data *dtree));
   local void set_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 |= (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 |= 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 |= (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 |= (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: */
       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;
   
       /* 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 _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 _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 _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;
       s->last_eob_len = 8; /* enough lookahead for inflate */
   #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 _tr_stored_block(s, buf, stored_len, eof)
       deflate_state *s;
       charf *buf;       /* input block */
       ulg stored_len;   /* length of input block */
       int eof;          /* true if this is the last block for a file */
   {
       send_bits(s, (STORED_BLOCK<<1)+eof, 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 */
   }
   
   /* ===========================================================================
    * Send one empty static block to give enough lookahead for inflate.
    * This takes 10 bits, of which 7 may remain in the bit buffer.
    * The current inflate code requires 9 bits of lookahead. If the
    * last two codes for the previous block (real code plus EOB) were coded
    * on 5 bits or less, inflate may have only 5+3 bits of lookahead to decode
    * the last real code. In this case we send two empty static blocks instead
    * of one. (There are no problems if the previous block is stored or fixed.)
    * To simplify the code, we assume the worst case of last real code encoded
    * on one bit only.
    */
   void _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);
       /* Of the 10 bits for the empty block, we have already sent
        * (10 - bi_valid) bits. The lookahead for the last real code (before
        * the EOB of the previous block) was thus at least one plus the length
        * of the EOB plus what we have just sent of the empty static block.
        */
       if (1 + s->last_eob_len + 10 - s->bi_valid < 9) {
           send_bits(s, STATIC_TREES<<1, 3);
           send_code(s, END_BLOCK, static_ltree);
   #ifdef DEBUG
           s->compressed_len += 10L;
   #endif
           bi_flush(s);
       }
       s->last_eob_len = 7;
   }
   
   /* ===========================================================================
    * Determine the best encoding for the current block: dynamic trees, static
    * trees or store, and output the encoded block to the zip file.
    */
   void _tr_flush_block(s, buf, stored_len, eof)
       deflate_state *s;
       charf *buf;       /* input block, or NULL if too old */
       ulg stored_len;   /* length of input block */
       int eof;          /* true 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 (stored_len > 0 && s->strm->data_type == Z_UNKNOWN)
               set_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, eof);
  
  #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)+eof, 3);
          compress_block(s, (ct_data *)static_ltree, (ct_data *)static_dtree);
  #ifdef DEBUG
          s->compressed_len += 3 + s->static_len;
  #endif
      } else {
          send_bits(s, (DYN_TREES<<1)+eof, 3);
          send_all_trees(s, s->l_desc.max_code+1, s->d_desc.max_code+1,
                         max_blindex+1);
          compress_block(s, (ct_data *)s->dyn_ltree, (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 (eof) {
          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*eof));
  }
  
  /* ===========================================================================
   * Save the match info and tally the frequency counts. Return true if
   * the current block must be flushed.
   */
  int _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;
      ct_data *ltree; /* literal tree */
      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);
      s->last_eob_len = ltree[END_BLOCK].Len;
  }
  
  /* ===========================================================================
   * Set the data type to BINARY or TEXT, using a crude approximation:
   * set it to Z_TEXT if all symbols are either printable characters (33 to 255)
   * or white spaces (9 to 13, or 32); or set it to Z_BINARY otherwise.
   * IN assertion: the fields Freq of dyn_ltree are set.
   */
  local void set_data_type(s)
      deflate_state *s;
  {
      int n;
  
      for (n = 0; n < 9; n++)
          if (s->dyn_ltree[n].Freq != 0)
              break;
      if (n == 9)
          for (n = 14; n < 32; n++)
              if (s->dyn_ltree[n].Freq != 0)
                  break;
      s->strm->data_type = (n == 32) ? Z_TEXT : 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 */
      s->last_eob_len = 8; /* enough lookahead for inflate */
  
      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++);
      }
  }

Cache object: 7fd0d47331ec152cf0745e37afea3ecc