uLong ZEXPORT deflateBound()

in zlib/deflate.c [834:897]

• 48 lines of code
• 18 McCabe index (conditional complexity)

uLong ZEXPORT deflateBound(z_streamp strm, uLong sourceLen) {
    deflate_state *s;
    uLong fixedlen, storelen, wraplen;

    /* upper bound for fixed blocks with 9-bit literals and length 255
       (memLevel == 2, which is the lowest that may not use stored blocks) --
       ~13% overhead plus a small constant */
    fixedlen = sourceLen + (sourceLen >> 3) + (sourceLen >> 8) +
               (sourceLen >> 9) + 4;

    /* upper bound for stored blocks with length 127 (memLevel == 1) --
       ~4% overhead plus a small constant */
    storelen = sourceLen + (sourceLen >> 5) + (sourceLen >> 7) +
               (sourceLen >> 11) + 7;

    /* if can't get parameters, return larger bound plus a wrapper */
    if (deflateStateCheck(strm))
        return (fixedlen > storelen ? fixedlen : storelen) + 18;

    /* compute wrapper length */
    s = strm->state;
    switch (s->wrap < 0 ? -s->wrap : s->wrap) {
    case 0:                                 /* raw deflate */
        wraplen = 0;
        break;
    case 1:                                 /* zlib wrapper */
        wraplen = 6 + (s->strstart ? 4 : 0);
        break;
#ifdef GZIP
    case 2:                                 /* gzip wrapper */
        wraplen = 18;
        if (s->gzhead != Z_NULL) {          /* user-supplied gzip header */
            Bytef *str;
            if (s->gzhead->extra != Z_NULL)
                wraplen += 2 + s->gzhead->extra_len;
            str = s->gzhead->name;
            if (str != Z_NULL)
                do {
                    wraplen++;
                } while (*str++);
            str = s->gzhead->comment;
            if (str != Z_NULL)
                do {
                    wraplen++;
                } while (*str++);
            if (s->gzhead->hcrc)
                wraplen += 2;
        }
        break;
#endif
    default:                                /* for compiler happiness */
        wraplen = 18;
    }

    /* if not default parameters, return one of the conservative bounds */
    if (s->w_bits != 15 || s->hash_bits != 8 + 7)
        return (s->w_bits <= s->hash_bits && s->level ? fixedlen : storelen) +
               wraplen;

    /* default settings: return tight bound for that case -- ~0.03% overhead
       plus a small constant */
    return sourceLen + (sourceLen >> 12) + (sourceLen >> 14) +
           (sourceLen >> 25) + 13 - 6 + wraplen;
}