Vielleicht geht's ja einfach mit float?
Zitat Zitat von gcc-3.4.4/gcc/config/avr/avr.h
#define FLOAT_TYPE_SIZE 32
/* A C expression for the size in bits of the type `float' on the
target machine. If you don't define this, the default is one word. */

#define DOUBLE_TYPE_SIZE 32
/* A C expression for the size in bits of the type `double' on the
target machine. If you don't define this, the default is two
words. */