// The first four bits is the CINFO (compression info), which is 7 for the default deflate window size.
	// The next four bits is the CM (compression method), which is 8 for deflate.
	z.scratch[0] = 0x78
	// The next two bits is the FLEVEL (compression level). The four values are:
	// 0=fastest, 1=fast, 2=default, 3=best.
	// The next bit, FDICT, is set if a dictionary is given.
	// The final five FCHECK bits form a mod-31 checksum.
	switch z.level {