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zlib-src/trees.c  view on Meta::CPAN

    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(deflate_state *s) {
    send_bits(s, STATIC_TREES<<1, 3);
    send_code(s, END_BLOCK, static_ltree);
#ifdef ZLIB_DEBUG
    s->compressed_len += 10L; /* 3 for block type, 7 for EOB */
#endif
    bi_flush(s);
}

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

    if (s->sym_next != 0) do {
#ifdef LIT_MEM
        dist = s->d_buf[sx];
        lc = s->l_buf[sx++];
#else
        dist = s->sym_buf[sx++] & 0xff;
        dist += (unsigned)(s->sym_buf[sx++] & 0xff) << 8;
        lc = s->sym_buf[sx++];
#endif
        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 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 -= (unsigned)base_dist[code];
                send_bits(s, (int)dist, extra); /* send the extra bits */
            }
        } /* literal or match pair ? */

        /* Check for no overlay of pending_buf on needed symbols */
#ifdef LIT_MEM
        Assert(s->pending < 2 * (s->lit_bufsize + sx), "pendingBuf overflow");
#else
        Assert(s->pending < s->lit_bufsize + sx, "pendingBuf overflow");
#endif

    } while (sx < s->sym_next);

    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
 *       "block list" (0..6, 14..25, 28..31).
 *    b) There is at least one printable character belonging to the
 *       "allow 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(deflate_state *s) {
    /* block_mask is the bit mask of block-listed bytes
     * set bits 0..6, 14..25, and 28..31
     * 0xf3ffc07f = binary 11110011111111111100000001111111
     */
    unsigned long block_mask = 0xf3ffc07fUL;
    int n;

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

    /* Check for textual ("allow-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 "block-listed" or "allow-listed" bytes:
     * this stream either is empty or has tolerated ("gray-listed") bytes only.
     */
    return Z_BINARY;
}

/* ===========================================================================
 * Determine the best encoding for the current block: dynamic trees, static
 * trees or store, and write out the encoded block.
 */
void ZLIB_INTERNAL _tr_flush_block(deflate_state *s, charf *buf,
                                   ulg stored_len, int last) {
    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 */