block_compress
unsigned long block_compress(const unsigned char *, unsigned long length,
tmp = (u_char)((maxbits) | block_compress);
free_ent = ((block_compress) ? FIRST : 256);
checkpoint && block_compress) {
block_compress = maxbits & BLOCK_MASK;
free_ent = block_compress ? FIRST : 256;
if ((code == CLEAR) && block_compress) {
block_compress = BLOCK_MASK;