Integer roots

[garnet420]

Consider adding support for integer roots, as it can be done somewhat faster than pow in general (and may be more accurate). This quick implementation is about 25% faster:

      Decimal.prototype.nthRoot = function (value) {
        if (this.mantissa === 0) return ME_NN(0, 0);
        if (value > 307) return this.pow(1 / value);
        if (value === 0) return ME_NN(1, 0);
        const newExp = Math.floor(this.exponent / value);
        const excessExp = this.exponent - value * newExp;
        return ME(Math.pow(powerOf10(excessExp) * this.mantissa, 1 / value), newExp);
      };

(It doesn't take the sign of the base into account, though)