Confirmed, in winavr float == double (source: "WinAVR / gccavr does not support doubles, in other words: double is considered as float" in http://www.avrfreaks.net/wiki/index.php/Documentation:AVR_Float) and also from the maintainer of avr-libc: http://www.avrfreaks.net/index.php?module=PNphpBB2&file=viewtopic&t=50770&highlight=