+/* zlib.h says that if we want to be able to compress something in a single
+ * call, avail_out must be at least 0.1% larger than avail_in plus 12 bytes.
+ * We'll add in 0.1%+16, just to be safe (and we'll avoid floating point,
+ * to ensure that this is a compile-time value). */
+#define AVAIL_OUT_SIZE(avail_in_size) ((avail_in_size)*1001/1000+16)
+