if err := x.setBytes(b, m); err != nil {
		return nil, err
	}
	leading := _W - bitLen(x.limbs[len(x.limbs)-1])
	if leading < m.leading {
		return nil, errors.New("input overflows the modulus size")
	}
	x.maybeSubtractModulus(no, m)
	return x, nil
}

// bigEndianUint returns the contents of buf interpreted as a
// big-endian encoded uint value.
func bigEndianUint(buf []byte) uint {
	if _W == 64 {