func precStr(s string) *big.Float {
	f, _ := new(big.Float).SetPrec(prec).SetString(s)
	return f
}
precStr wraps the conversion from a string into a big.Float. For results that
actually can be represented exactly, this should only be used on values that
are integer multiples of integer powers of 2.
package r3
import (
	"fmt"
	"math/big"
)
const (
	prec = big.MaxPrec
)
var (
	precise0 = precInt(0)
	precise1 = precInt(1)
)