When you archive for OS X or iOS, Xcode 7.3 reports the following error:
/Users/brendan/Projects/iPhone/UnzipKit/Source/UZKArchive.m:404:58: error: implicit conversion increases floating-point precision: 'float' to 'CGFloat' (aka 'double') [-Werror,-Wdouble-promotion]
progress(info, bytesDecompressed / totalSize.floatValue);
~~~~~~~~ ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
Changing that line to totalSize.doubleValue fixes the problem.