// The number n is known to be non-zero.
func (n nat) probablyPrimeMillerRabin(reps int, force2 bool) bool {
	nm1 := nat(nil).sub(n, natOne)
	// determine q, k such that nm1 = q << k
	k := nm1.trailingZeroBits()
	q := nat(nil).shr(nm1, k)

	nm3 := nat(nil).sub(nm1, natTwo)
	rand := rand.New(rand.NewSource(int64(n[0])))

	var x, y, quotient nat
	nm3Len := nm3.bitLen()

NextRandom:

	// changes must be reviewed by a security expert.
	return x.abs.bitLen()
}

// TrailingZeroBits returns the number of consecutive least significant zero
// bits of |x|.
func (x *Int) TrailingZeroBits() uint {
	return x.abs.trailingZeroBits()
}

// Exp sets z = x**y mod |m| (i.e. the sign of m is ignored), and returns z.

	d := x.Denom().abs // d >= 1

	// Determine p2 by counting factors of 2.
	// p2 corresponds to the trailing zero bits in d.
	// Do this first to reduce q as much as possible.
	var q nat
	p2 := d.trailingZeroBits()
	q = q.shr(d, p2)

	// Determine p5 by counting factors of 5.
	// Build a table starting with an initial power of 5,
	// and use repeated squaring until the factor doesn't

		top |= top >> 16
		top |= top >> 16 >> 16 // ">> 32" doesn't compile on 32-bit architectures
		return i*_W + bits.Len(top)
	}
	return 0
}

// trailingZeroBits returns the number of consecutive least significant zero
// bits of x.
func (x nat) trailingZeroBits() uint {
	if len(x) == 0 {
		return 0
	}
	var i uint
	for x[i] == 0 {
		i++
	}
	// x[i] != 0

// The result is 0 for |x| == 0 and |x| == Inf.
func (x *Float) MinPrec() uint {
	if x.form != finite {
		return 0
	}
	return uint(len(x.mant))*_W - x.mant.trailingZeroBits()
}

// Mode returns the rounding mode of x.
func (x *Float) Mode() RoundingMode {
	return x.mode
}

// Acc returns the accuracy of x produced by the most recent