local int dynamic(struct state *s)
{
    int nlen, ndist, ncode;             /* number of lengths in descriptor */
    int index;                          /* index of lengths[] */
    int err;                            /* construct() return value */
    short lengths[MAXCODES];            /* descriptor code lengths */
    short lencnt[MAXBITS+1], lensym[MAXLCODES];         /* lencode memory */
    short distcnt[MAXBITS+1], distsym[MAXDCODES];       /* distcode memory */
    struct huffman lencode, distcode;   /* length and distance codes */
    static const short order[19] =      /* permutation of code length codes */
        {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};

    /* construct lencode and distcode */
    lencode.count = lencnt;
    lencode.symbol = lensym;
    distcode.count = distcnt;
    distcode.symbol = distsym;

    /* get number of lengths in each table, check lengths */
    nlen = bits(s, 5) + 257;
    ndist = bits(s, 5) + 1;
    ncode = bits(s, 4) + 4;
    if (nlen > MAXLCODES || ndist > MAXDCODES)
        return -3;                      /* bad counts */

    /* read code length code lengths (really), missing lengths are zero */
    for (index = 0; index < ncode; index++)
        lengths[order[index]] = bits(s, 3);
    for (; index < 19; index++)
        lengths[order[index]] = 0;

    /* build huffman table for code lengths codes (use lencode temporarily) */
    err = construct(&lencode, lengths, 19);
    if (err != 0)               /* require complete code set here */
        return -4;

    /* read length/literal and distance code length tables */
    index = 0;
    while (index < nlen + ndist) {
        int symbol;             /* decoded value */
        int len;                /* last length to repeat */

        symbol = decode(s, &lencode);
        if (symbol < 0)
            return symbol;          /* invalid symbol */
        if (symbol < 16)                /* length in 0..15 */
            lengths[index++] = symbol;
        else {                          /* repeat instruction */
            len = 0;                    /* assume repeating zeros */
            if (symbol == 16) {         /* repeat last length 3..6 times */
                if (index == 0)
                    return -5;          /* no last length! */
                len = lengths[index - 1];       /* last length */
                symbol = 3 + bits(s, 2);
            }
            else if (symbol == 17)      /* repeat zero 3..10 times */
                symbol = 3 + bits(s, 3);
            else                        /* == 18, repeat zero 11..138 times */
                symbol = 11 + bits(s, 7);
            if (index + symbol > nlen + ndist)
                return -6;              /* too many lengths! */
            while (symbol--)            /* repeat last or zero symbol times */
                lengths[index++] = len;
        }
    }

    /* check for end-of-block code -- there better be one! */
    if (lengths[256] == 0)
        return -9;

    /* build huffman table for literal/length codes */
    err = construct(&lencode, lengths, nlen);
    if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1]))
        return -7;      /* incomplete code ok only for single length 1 code */

    /* build huffman table for distance codes */
    err = construct(&distcode, lengths + nlen, ndist);
    if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1]))
        return -8;      /* incomplete code ok only for single length 1 code */

    /* decode data until end-of-block code */
    return codes(s, &lencode, &distcode);
}