bigprime.java

一个计算梅里森素数的Java程序

package numbercruncher.program12_1;

import java.math.BigInteger;
import java.util.Random;

/**
 * PROGRAM 12-1: Big Prime Number
 *
 * Demonstrate BigInteger by computing
 * the Mersenne prime 2^11213 - 1.
 */
public class BigPrime
{
    private static final int EXPONENT = 11213;

    /** the prime number */     private BigInteger prime;

    /**
     * Compute and print 2^EXPONENT - 1.
     */
    private void compute() throws Exception
    {
        // Compute the value.
        prime = BigInteger.valueOf(1);
        for (int i = 1; i <= EXPONENT; ++i) {
            prime = prime.add(prime);
        }
        prime = prime.subtract(BigInteger.valueOf(1));

        // Print it.
        System.out.println("2^" + EXPONENT + " - 1 = ");
        print(prime);
    }

    /**
     * Print the big prime number.
     * @param prime the big prime number
     */
    private void print(BigInteger prime)
    {
        String primeString = prime.toString();

        int length   = primeString.length();
        int groups   = length/3;    // no. of groups of three digits
        int exGroups = length%3;    // no. of extra-group digits
        int lines    = groups/16;   // no. of lines of 16 groups
        int exLines  = groups%16;   // no. of extra-line groups

        int index     = 0;          // substring index
        int lineWidth = 4*16;

        // Print a right-justified partial line, if any.
        if (exLines > 0) {
            int padding = lineWidth - 4*exLines - exGroups - 1;
            for (int i = 0; i < padding; ++i) System.out.print(" ");

            // Print the extra-group digits.
            System.out.print(primeString.substring(0, exGroups) + ",");
            index = exGroups;

            // Print the extra-line groups.
            for (int i = 0; i < exLines; ++i) {
                index = printGroup(primeString, index, length);
            }
            System.out.println();
        }

        int count = 0;  // group counter

        // Loop to print whole lines.
        while (index < length) {
            index = printGroup(primeString, index, length);

            // End of line?
            if (++count == 16) {
                System.out.println();
                count = 0;
            }
        }

        // Print statistics.
        System.out.println();
        System.out.println("Number of digits = " + length);
        System.out.println("Number of bits   = " + prime.bitLength());
    }

    /**
     * Print a group of digits followed by a comma.
     * @param primeString the prime number as a string
     * @param index the substring index
     * @param length the string length
     * @return the new index value
     */
    private int printGroup(String primeString, int index, int length)
    {
        System.out.print(primeString.substring(index, index += 3));

        // Append a comma unless it's the last group.
        if (index < length) System.out.print(",");

        return index;
    }

    /**
     * Main.
     * @param args the array of program arguments
     */
    public static void main(String args[])
    {
        try {
            BigPrime bp = new BigPrime();
            bp.compute();
        }
        catch(Exception ex) {
            System.out.println("ERROR: " + ex.getMessage());
        }
    }
}
/*
Output:
2^11213 - 1 =
                                          2,814,112,013,697,373,
133,393,152,975,842,584,191,818,662,382,013,600,787,892,419,349,
345,515,176,682,276,313,810,715,094,745,633,257,074,198,789,308,
535,071,537,342,445,016,418,881,801,789,390,548,709,414,391,857,
257,571,565,758,706,478,418,356,747,070,674,633,497,188,053,050,
875,416,821,624,325,680,555,826,071,110,691,946,607,460,873,056,
965,360,830,571,590,242,774,934,226,866,183,966,309,185,433,462,
514,537,484,258,655,982,386,235,046,029,227,507,801,410,907,163,
348,439,547,781,093,397,260,096,909,677,091,843,944,555,754,221,
115,477,343,760,206,979,650,067,087,884,993,478,012,977,277,878,
532,807,432,236,554,020,931,571,802,310,429,923,167,588,432,457,
036,104,110,850,960,439,769,038,450,365,514,022,349,625,383,665,
751,207,169,661,697,352,732,236,111,926,846,454,751,701,734,527,
011,379,148,175,107,820,821,297,628,946,795,631,098,960,767,492,
250,494,834,254,073,334,414,121,627,833,939,461,539,212,528,932,
010,726,136,689,293,688,815,665,491,671,395,174,710,452,663,709,
175,753,603,774,156,855,766,515,313,827,613,727,281,696,692,633,
529,666,363,787,286,539,769,941,609,107,777,183,593,336,002,680,
124,517,633,451,490,439,598,324,823,836,457,251,219,406,391,432,
635,639,225,604,556,042,396,004,307,799,361,927,379,900,586,400,
420,763,092,320,813,392,262,492,942,076,312,933,268,033,818,471,
555,255,820,639,308,889,948,665,570,202,403,815,856,313,578,949,
779,767,046,261,845,327,956,725,767,289,205,262,311,752,014,786,
247,813,331,834,015,084,475,386,760,526,612,217,340,579,721,237,
414,485,803,725,355,463,022,009,536,301,008,145,867,524,704,604,
618,862,039,093,555,206,195,328,240,951,895,107,040,793,284,825,
095,462,530,151,872,823,997,171,764,140,663,315,804,309,008,611,
942,578,380,931,064,748,991,594,407,476,328,437,785,848,825,423,
921,170,614,938,294,029,483,257,162,979,299,388,940,695,877,375,
448,948,081,108,345,293,394,327,808,452,729,789,834,135,140,193,
912,419,661,799,488,795,210,328,238,112,742,218,700,634,541,149,
743,657,287,232,843,426,369,348,804,878,993,471,962,403,393,967,
857,676,150,371,600,196,650,252,168,250,117,793,178,488,012,000,
505,422,821,362,550,520,509,209,724,459,895,852,366,827,477,851,
619,190,503,254,853,115,029,403,132,178,989,005,195,751,194,301,
340,277,282,730,390,683,651,120,587,895,060,198,753,121,882,187,
788,657,024,007,291,784,186,518,589,977,788,510,306,743,945,896,
108,645,258,766,415,692,825,664,174,470,616,153,305,144,852,273,
884,549,635,059,255,410,606,458,427,323,864,109,506,687,636,314,
447,514,269,094,932,953,219,924,212,594,695,157,655,009,158,521,
173,420,923,275,882,063,327,625,408,617,963,032,962,033,572,563,
553,604,056,097,832,111,547,535,908,988,433,816,919,747,615,817,
161,606,620,557,307,000,377,194,730,013,431,815,560,750,159,027,
842,164,901,422,544,571,224,546,936,793,234,970,894,954,668,425,
436,412,347,785,376,194,310,030,139,080,568,383,420,772,628,618,
722,646,109,707,506,566,928,102,800,033,961,704,343,991,962,002,
059,794,565,527,774,913,883,237,756,792,720,065,543,768,640,792,
177,441,559,278,272,350,823,092,843,683,534,396,679,150,229,676,
101,834,243,787,820,420,087,274,028,617,212,684,576,388,733,605,
769,491,224,109,866,592,577,360,666,241,467,280,158,988,605,523,
486,345,880,882,227,855,505,706,309,276,349,415,034,547,677,180,
618,296,352,866,263,005,509,222,254,318,459,768,194,126,727,603,
047,460,344,175,581,029,298,320,171,226,355,234,439,676,816,309,
919,127,574,206,334,807,719,021,875,413,891,580,871,529,049,187,
829,308,412,133,400,910,419,756,313,021,540,478,436,604,178,446,
757,738,998,632,083,586,207,992,234,085,162,634,375,406,771,169,
707,323,213,988,284,943,779,122,171,985,953,605,897,902,291,781,
768,286,548,287,878,180,415,060,635,460,047,164,104,095,483,777,
201,737,468,873,324,068,550,430,695,826,210,304,316,336,385,311,
384,093,490,021,332,372,463,463,373,977,427,405,896,673,827,544,
203,128,574,874,581,960,335,232,005,637,229,319,592,369,288,171,
375,276,702,260,450,911,735,069,504,025,016,667,755,214,932,073,
643,654,199,488,477,010,363,909,372,005,757,899,989,580,775,775,
126,621,113,057,905,717,449,417,222,016,070,530,243,916,116,705,
990,451,304,256,206,318,289,297,738,303,095,152,430,549,772,239,
514,964,821,601,838,628,861,446,301,936,017,710,546,777,503,109,
263,030,994,747,397,618,576,207,373,447,725,441,427,135,362,428,
360,863,669,327,157,635,983,045,447,971,816,718,801,639,869,547,
525,146,305,655,571,843,717,916,875,669,140,320,724,978,568,586,
718,527,586,602,439,602,335,283,513,944,980,064,327,030,278,104,
224,144,971,883,680,541,689,784,796,267,391,476,087,696,392,191

Number of digits = 3376
Number of bits   = 11213
*/