The cast from floatbv to fixedbv is not implemented. This example gives the following warning: void main() { __CPROVER_floatbv[32][23] float_a; __CPROVER_fixedbv[24][12] fixed_b; float_a = 2.14; fixed_b = 2.5; float_a = (__CPROVER_floatbv[32][23])fixed_b; __CPROVER_assert(0, ""); } warning: ignoring typecast * type: floatbv * width: 32 * f: 23 * #source_location: * file: floatcast.c * line: 10 The cast the other way round, from fixedbv to floatbv, does seem to be implemented.