package client;import compute.*;import java.math.*;public class Pi implements Task {    /** constants used in pi computation */    private static final BigDecimal ZERO =         BigDecimal.valueOf(0);    private static final BigDecimal  ONE =         BigDecimal.valueOf(1);    private static final BigDecimal FOUR =         BigDecimal.valueOf(4);    /** rounding mode to use during pi computation */    private static final int roundingMode =         BigDecimal.ROUND_HALF_EVEN;    /** digits of precision after the decimal point */    private int digits;        /**     * Construct a task to calculate pi to the specified     * precision.     */    public Pi(int digits) {        this.digits = digits;    }    /**     * Calculate pi.     */    public Object execute() {        return computePi(digits);    }    /**     * Compute the value of pi to the specified number of      * digits after the decimal point.  The value is      * computed using Machin's formula:     *     *          pi/4 = 4*arctan(1/5) - arctan(1/239)     *     * and a power series expansion of arctan(x) to      * sufficient precision.     */    public static BigDecimal computePi(int digits) {        int scale = digits + 5;        BigDecimal arctan1_5 = arctan(5, scale);        BigDecimal arctan1_239 = arctan(239, scale);        BigDecimal pi = arctan1_5.multiply(FOUR).subtract(                                  arctan1_239).multiply(FOUR);        return pi.setScale(digits,                            BigDecimal.ROUND_HALF_UP);    }    /**     * Compute the value, in radians, of the arctangent of      * the inverse of the supplied integer to the speficied     * number of digits after the decimal point.  The value     * is computed using the power series expansion for the     * arc tangent:     *     * arctan(x) = x - (x^3)/3 + (x^5)/5 - (x^7)/7 +      *     (x^9)/9 ...     */       public static BigDecimal arctan(int inverseX,                                   int scale)     {        BigDecimal result, numer, term;        BigDecimal invX = BigDecimal.valueOf(inverseX);        BigDecimal invX2 =             BigDecimal.valueOf(inverseX * inverseX);        numer = ONE.divide(invX, scale, roundingMode);        result = numer;        int i = 1;        do {            numer =                 numer.divide(invX2, scale, roundingMode);            int denom = 2 * i + 1;            term =                 numer.divide(BigDecimal.valueOf(denom),                             scale, roundingMode);            if ((i % 2) != 0) {                result = result.subtract(term);            } else {                result = result.add(term);            }            i++;        } while (term.compareTo(ZERO) != 0);        return result;    }}