A.6.3 Integer and Floating
When a value of floating type is converted to integral type, the fractional part is discarded; if the resulting value cannot be represented in the integral type, the behavior is undefined. In particular, the result of converting negative floating values to unsigned integral types is not specified.
When a value of integral type is converted to floating, and the value is in the representable range but is not exactly representable, then the result may be either the next higher or next lower representable value. If the result is out of range, the behavior is undefined.