+ /* We overlay pending_buf and sym_buf. This works since the average size
+ * for length/distance pairs over any compressed block is assured to be 31
+ * bits or less.
+ *
+ * Analysis: The longest fixed codes are a length code of 8 bits plus 5
+ * extra bits, for lengths 131 to 257. The longest fixed distance codes are
+ * 5 bits plus 13 extra bits, for distances 16385 to 32768. The longest
+ * possible fixed-codes length/distance pair is then 31 bits total.
+ *
+ * sym_buf starts one-fourth of the way into pending_buf. So there are
+ * three bytes in sym_buf for every four bytes in pending_buf. Each symbol
+ * in sym_buf is three bytes -- two for the distance and one for the
+ * literal/length. As each symbol is consumed, the pointer to the next
+ * sym_buf value to read moves forward three bytes. From that symbol, up to
+ * 31 bits are written to pending_buf. The closest the written pending_buf
+ * bits gets to the next sym_buf symbol to read is just before the last
+ * code is written. At that time, 31*(n-2) bits have been written, just
+ * after 24*(n-2) bits have been consumed from sym_buf. sym_buf starts at
+ * 8*n bits into pending_buf. (Note that the symbol buffer fills when n-1
+ * symbols are written.) The closest the writing gets to what is unread is
+ * then n+14 bits. Here n is lit_bufsize, which is 16384 by default, and
+ * can range from 128 to 32768.
+ *
+ * Therefore, at a minimum, there are 142 bits of space between what is
+ * written and what is read in the overlain buffers, so the symbols cannot
+ * be overwritten by the compressed data. That space is actually 139 bits,
+ * due to the three-bit fixed-code block header.
+ *
+ * That covers the case where either Z_FIXED is specified, forcing fixed
+ * codes, or when the use of fixed codes is chosen, because that choice
+ * results in a smaller compressed block than dynamic codes. That latter
+ * condition then assures that the above analysis also covers all dynamic
+ * blocks. A dynamic-code block will only be chosen to be emitted if it has
+ * fewer bits than a fixed-code block would for the same set of symbols.
+ * Therefore its average symbol length is assured to be less than 31. So
+ * the compressed data for a dynamic block also cannot overwrite the
+ * symbols from which it is being constructed.
+ */
+
+ s->pending_buf = (uchf *) ZALLOC(strm, s->lit_bufsize, 4);
+ s->pending_buf_size = (ulg)s->lit_bufsize * 4;