func newRat() *big.Rat     { return new(big.Rat) }
func newFloat() *big.Float { return new(big.Float).SetPrec(prec) }

func i64toi(x int64Val) intVal   { return intVal{newInt().SetInt64(int64(x))} }
func i64tor(x int64Val) ratVal   { return ratVal{newRat().SetInt64(int64(x))} }
func i64tof(x int64Val) floatVal { return floatVal{newFloat().SetInt64(int64(x))} }
func itor(x intVal) ratVal       { return ratVal{newRat().SetInt(x.val)} }