text: /* trees.c -- output deflated data using Huffman coding
   * Copyright (C) 1995-2017 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.
   */
  
  #include "zbuild.h"
  #include "deflate.h"
  #include "trees_p.h"
  #include "trees_emit.h"
  #include "trees.h"
  
  /* 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.
   */
  
  struct static_tree_desc_s {
      const ct_data *static_tree; /* static tree or NULL */
      const int     *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 */
      unsigned int   max_length;  /* max bit length for the codes */
  };
  
  static const static_tree_desc  static_l_desc =
  {static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS};
  
  static const static_tree_desc  static_d_desc =
  {static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS};
  
  static const static_tree_desc  static_bl_desc =
  {(const ct_data *)0, extra_blbits, 0,   BL_CODES, MAX_BL_BITS};
  
  /* ===========================================================================
   * Local (static) routines in this file.
   */
  
  static void init_block       (deflate_state *s);
  static void pqdownheap       (deflate_state *s, ct_data *tree, int k);
  static void gen_bitlen       (deflate_state *s, tree_desc *desc);
  static void build_tree       (deflate_state *s, tree_desc *desc);
  static void scan_tree        (deflate_state *s, ct_data *tree, int max_code);
  static void send_tree        (deflate_state *s, ct_data *tree, int max_code);
  static int  build_bl_tree    (deflate_state *s);
  static void send_all_trees   (deflate_state *s, int lcodes, int dcodes, int blcodes);
  static void compress_block   (deflate_state *s, const ct_data *ltree, const ct_data *dtree);
  static int  detect_data_type (deflate_state *s);
  static void bi_flush         (deflate_state *s);
  
  /* ===========================================================================
   * Initialize the tree data structures for a new zlib stream.
   */
  void ZLIB_INTERNAL zng_tr_init(deflate_state *s) {
      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 ZLIB_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.
   */
  static void init_block(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->sym_next = 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).
   */
  static void pqdownheap(deflate_state *s, ct_data *tree, int k) {
      /* tree: the tree to restore */
      /* 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.
   */
  static void gen_bitlen(deflate_state *s, tree_desc *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 int *extra        = desc->stat_desc->extra_bits;
      int base                = desc->stat_desc->extra_base;
      unsigned int max_length = desc->stat_desc->max_length;
      int h;              /* heap index */
      int n, m;           /* iterate over the tree elements */
      unsigned int bits;  /* bit length */
      int xbits;          /* extra bits */
      uint16_t 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 = (uint16_t)bits;
          /* We overwrite tree[n].Dad which is no longer needed */
  
          if (n > max_code) /* not a leaf node */
              continue;
  
          s->bl_count[bits]++;
          xbits = 0;
          if (n >= base)
              xbits = extra[n-base];
          f = tree[n].Freq;
          s->opt_len += (unsigned long)f * (unsigned int)(bits + xbits);
          if (stree)
              s->static_len += (unsigned long)f * (unsigned int)(stree[n].Len + xbits);
      }
      if (overflow == 0)
          return;
  
      Tracev((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 (tree[m].Len != bits) {
                  Tracev((stderr, "code %d bits %d->%u\n", m, tree[m].Len, bits));
                  s->opt_len += (unsigned long)(bits * tree[m].Freq);
                  s->opt_len -= (unsigned long)(tree[m].Len * tree[m].Freq);
                  tree[m].Len = (uint16_t)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.
   */
  ZLIB_INTERNAL void gen_codes(ct_data *tree, int max_code, uint16_t *bl_count) {
      /* tree: the tree to decorate */
      /* max_code: largest code with non zero frequency */
      /* bl_count: number of codes at each bit length */
      uint16_t next_code[MAX_BITS+1];  /* next code value for each bit length */
      unsigned int 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++) {
          code = (code + bl_count[bits-1]) << 1;
          next_code[bits] = (uint16_t)code;
      }
      /* 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 = (uint16_t)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.
   */
  static void build_tree(deflate_state *s, tree_desc *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] = (unsigned char)((s->depth[n] >= s->depth[m] ?
                                            s->depth[n] : s->depth[m]) + 1);
          tree[n].Dad = tree[m].Dad = (uint16_t)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.
   */
  static void scan_tree(deflate_state *s, ct_data *tree, int max_code) {
      /* tree: the tree to be scanned */
      /* 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 */
      uint16_t count = 0;        /* repeat count of the current code */
      uint16_t max_count = 7;    /* max repeat count */
      uint16_t min_count = 4;    /* min repeat count */
  
      if (nextlen == 0)
          max_count = 138, min_count = 3;
  
      tree[max_code+1].Len = (uint16_t)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.
   */
  static void send_tree(deflate_state *s, ct_data *tree, int max_code) {
      /* tree: the tree to be scanned */
      /* 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;
  
      // Temp local variables
      uint32_t bi_valid = s->bi_valid;
      uint64_t bi_buf = s->bi_buf;
  
      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, bi_buf, bi_valid);
              } while (--count != 0);
  
          } else if (curlen != 0) {
              if (curlen != prevlen) {
                  send_code(s, curlen, s->bl_tree, bi_buf, bi_valid);
                  count--;
              }
              Assert(count >= 3 && count <= 6, " 3_6?");
              send_code(s, REP_3_6, s->bl_tree, bi_buf, bi_valid);
              send_bits(s, count-3, 2, bi_buf, bi_valid);
  
          } else if (count <= 10) {
              send_code(s, REPZ_3_10, s->bl_tree, bi_buf, bi_valid);
              send_bits(s, count-3, 3, bi_buf, bi_valid);
  
          } else {
              send_code(s, REPZ_11_138, s->bl_tree, bi_buf, bi_valid);
              send_bits(s, count-11, 7, bi_buf, bi_valid);
          }
          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;
          }
      }
  
      // Store back temp variables
      s->bi_buf = bi_buf;
      s->bi_valid = bi_valid;
  }
  
  /* ===========================================================================
   * Construct the Huffman tree for the bit lengths and return the index in
   * bl_order of the last bit length code to send.
   */
  static int build_bl_tree(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*((unsigned long)max_blindex+1) + 5+5+4;
      Tracev((stderr, "\ndyn trees: dyn %lu, stat %lu", 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.
   */
  static void send_all_trees(deflate_state *s, int lcodes, int dcodes, int blcodes) {
      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");
  
      // Temp local variables
      uint32_t bi_valid = s->bi_valid;
      uint64_t bi_buf = s->bi_buf;
  
      Tracev((stderr, "\nbl counts: "));
      send_bits(s, lcodes-257, 5, bi_buf, bi_valid); /* not +255 as stated in appnote.txt */
      send_bits(s, dcodes-1,   5, bi_buf, bi_valid);
      send_bits(s, blcodes-4,  4, bi_buf, bi_valid); /* not -3 as stated in appnote.txt */
      for (rank = 0; rank < blcodes; rank++) {
          Tracev((stderr, "\nbl code %2u ", bl_order[rank]));
          send_bits(s, s->bl_tree[bl_order[rank]].Len, 3, bi_buf, bi_valid);
      }
      Tracev((stderr, "\nbl tree: sent %lu", s->bits_sent));
  
      // Store back temp variables
      s->bi_buf = bi_buf;
      s->bi_valid = bi_valid;
  
      send_tree(s, (ct_data *)s->dyn_ltree, lcodes-1); /* literal tree */
      Tracev((stderr, "\nlit tree: sent %lu", s->bits_sent));
  
      send_tree(s, (ct_data *)s->dyn_dtree, dcodes-1); /* distance tree */
      Tracev((stderr, "\ndist tree: sent %lu", s->bits_sent));
  }
  
  /* ===========================================================================
   * Send a stored block
   */
  void ZLIB_INTERNAL zng_tr_stored_block(deflate_state *s, char *buf, unsigned long stored_len, int last) {
      /* buf: input block */
      /* stored_len: length of input block */
      /* last: one if this is the last block for a file */
      zng_tr_emit_tree(s, STORED_BLOCK, last); /* send block type */
      zng_tr_emit_align(s);                    /* align on byte boundary */
      cmpr_bits_align(s);
      put_short(s, (uint16_t)stored_len);
      put_short(s, (uint16_t)~stored_len);
      cmpr_bits_add(s, 32);
      sent_bits_add(s, 32);
      if (stored_len) {
          memcpy(s->pending_buf + s->pending, (unsigned char *)buf, stored_len);
          s->pending += stored_len;
          cmpr_bits_add(s, stored_len << 3);
          sent_bits_add(s, stored_len << 3);
      }
  }
  
  /* ===========================================================================
   * Flush the bits in the bit buffer to pending output (leaves at most 7 bits)
   */
  void ZLIB_INTERNAL zng_tr_flush_bits(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 zng_tr_align(deflate_state *s) {
      zng_tr_emit_tree(s, STATIC_TREES, 0);
      zng_tr_emit_end_block(s, static_ltree, 0);
      bi_flush(s);
  }
  
  /* ===========================================================================
   * Determine the best encoding for the current block: dynamic trees, static
   * trees or store, and write out the encoded block.
   */
  void ZLIB_INTERNAL zng_tr_flush_block(deflate_state *s, char *buf, unsigned long stored_len, int last) {
      /* buf: input block, or NULL if too old */
      /* stored_len: length of input block */
      /* last: one if this is the last block for a file */
      unsigned long 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 %lu, stat %lu", s->opt_len, s->static_len));
  
          build_tree(s, (tree_desc *)(&(s->d_desc)));
          Tracev((stderr, "\ndist data: dyn %lu, stat %lu", 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->sym_next / 3));
  
          if (static_lenb <= opt_lenb)
              opt_lenb = static_lenb;
  
      } else {
          Assert(buf != NULL, "lost buf");
          opt_lenb = static_lenb = stored_len + 5; /* force a stored block */
      }
  
  #ifdef FORCE_STORED
      if (buf != NULL) { /* force stored block */
  #else
      if (stored_len+4 <= opt_lenb && buf != NULL) {
          /* 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.
           */
          zng_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
          zng_tr_emit_tree(s, STATIC_TREES, last);
          compress_block(s, (const ct_data *)static_ltree, (const ct_data *)static_dtree);
          cmpr_bits_add(s, s->static_len);
      } else {
          zng_tr_emit_tree(s, DYN_TREES, last);
          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);
          cmpr_bits_add(s, s->opt_len);
      }
      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 unsigned long implemented on 32 bits.
       */
      init_block(s);
  
      if (last) {
          zng_tr_emit_align(s);
      }
      Tracev((stderr, "\ncomprlen %lu(%lu) ", s->compressed_len>>3, s->compressed_len-7*last));
  }
  
  /* ===========================================================================
   * Send the block data compressed using the given Huffman trees
   */
  static void compress_block(deflate_state *s, const ct_data *ltree, const ct_data *dtree) {
      /* ltree: literal tree */
      /* dtree: distance tree */
      unsigned dist;      /* distance of matched string */
      int lc;             /* match length or unmatched char (if dist == 0) */
      unsigned sx = 0;    /* running index in sym_buf */
  
      if (s->sym_next != 0) {
          do {
              dist = s->sym_buf[sx++] & 0xff;
              dist += (unsigned)(s->sym_buf[sx++] & 0xff) << 8;
              lc = s->sym_buf[sx++];
              if (dist == 0) {
                  zng_emit_lit(s, ltree, lc);
              } else {
                  zng_emit_dist(s, ltree, dtree, lc, dist);
              } /* literal or match pair ? */
  
              /* Check that the overlay between pending_buf and sym_buf is ok: */
              Assert(s->pending < s->lit_bufsize + sx, "pending_buf overflow");
          } while (sx < s->sym_next);
      }
  
      zng_emit_end_block(s, ltree, 0);
  }
  
  /* ===========================================================================
   * 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.
   */
  static int detect_data_type(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;
  }
  
  /* ===========================================================================
   * Flush the bit buffer, keeping at most 7 bits in it.
   */
  static void bi_flush(deflate_state *s) {
      if (s->bi_valid == 64) {
          put_uint64(s, s->bi_buf);
          s->bi_buf = 0;
          s->bi_valid = 0;
      } else {
          if (s->bi_valid >= 32) {
              put_uint32(s, (uint32_t)s->bi_buf);
              s->bi_buf >>= 32;
              s->bi_valid -= 32;
          }
          if (s->bi_valid >= 16) {
              put_short(s, (uint16_t)s->bi_buf);
              s->bi_buf >>= 16;
              s->bi_valid -= 16;
          }
          if (s->bi_valid >= 8) {
              put_byte(s, s->bi_buf);
              s->bi_buf >>= 8;
              s->bi_valid -= 8;
          }
      }
  }
  
  /* ===========================================================================
   * Reverse the first len bits of a code, using straightforward code (a faster
   * method would use a table)
   * IN assertion: 1 <= len <= 15
   */
  ZLIB_INTERNAL unsigned bi_reverse(unsigned code, int len) {
      /* code: the value to invert */
      /* len: its bit length */
      ZLIB_REGISTER unsigned res = 0;
      do {
          res |= code & 1;
          code >>= 1, res <<= 1;
      } while (--len > 0);
      return res >> 1;
  }
  