commonNaNToFloat64
if ( aSig ) return commonNaNToFloat64( float32ToCommonNaN( a ) );
if ( aSig ) return commonNaNToFloat64( float32ToCommonNaN( a ) );
return commonNaNToFloat64( floatx80ToCommonNaN( a ) );
return commonNaNToFloat64( float128ToCommonNaN( a ) );