Method integerPower

context.go:999–1038

integerPower sets d = x**y. d and x must not point to the same Decimal.

(d, x *Decimal, y *BigInt)

// integerPower sets d = x**y. d and x must not point to the same Decimal.
func (c *Context) integerPower(d, x *Decimal, y *BigInt) (Condition, error) {
	// See: https://en.wikipedia.org/wiki/Exponentiation_by_squaring.

	var b BigInt
	b.Set(y)
	neg := b.Sign() < 0
	if neg {
		b.Abs(&b)
	}

	var n Decimal
	n.Set(x)
	z := d
	z.Set(decimalOne)
	ed := MakeErrDecimal(c)
	for b.Sign() > 0 {
		if b.Bit(0) == 1 {
			ed.Mul(z, z, &n)
		}
		b.Rsh(&b, 1)

		// Only compute the next n if we are going to use it. Otherwise n can overflow
		// on the last iteration causing this to error.
		if b.Sign() > 0 {
			ed.Mul(&n, &n, &n)
		}
		if err := ed.Err(); err != nil {
			// In the negative case, convert overflow to underflow.
			if neg {
				ed.Flags = ed.Flags.negateOverflowFlags()
			}
			return ed.Flags, err
		}
	}

	if neg {
		ed.Quo(z, decimalOne, z)
	}
	return ed.Flags, ed.Err()
}

// Pow sets d = x**y.
func (c *Context) Pow(d, x, y *Decimal) (Condition, error) {