Name: bsC130419 Date: 07/24/2001


[probably 1.1.8 -- but see test results below for 1.3.x and 1.4 beta]

I'm operating in MacOS 9.1 with Metrowerks and I'm not sure if I've selected
the right options - inparticular I'm interested in a class from java.math which
doesn't seem to be listed above - but I think my bug (or feature? see below) is
possibly platform independent.


I'm not sure if this is a bug or a feature. In The constructor BigInteger(int
bitLength, int certainty, Random rnd) claims that it constructs a randomly
generated positive BigInteger that is probably prime, with the specified
bitLength.

Should this mean that the prime is between 0 and 2^bitLength? It appears that
it is between 2^(bitLength-1) and 2^bitLength as the following program
demonstrates:

/**
 * LargePrimes.java
 *
 * Description:
 * @author ad
 * @version
 */

import java.math.*;
import java.util.*;

public class LargePrimes {
public LargePrimes() {
}

static int power(int n)
{
int i,j=1;
for (i=1;i<=n;i++) j *= 2;
return j;
}

// Main entry point
static public void main(String[] args) {
int bits = 7;
int powbits = power(bits);
int [] tally = new int[powbits];
int i;
for (i = 0; i < powbits; i++){tally[i] = 0;}
Random r = new Random();
for (i = 1; i <= 10000; i++)
{ BigInteger prime = new BigInteger(bits, 10, r);
tally[prime.intValue()]++;
}
for (i = 0; i < powbits; i++)
{
if(tally[i] != 0){System.out.println(" " + i + " " + tally[i]);}
}
}

}

which gives output:

 67 744
 71 811
 73 744
 79 748
 83 753
 89 830
 97 764
 101 743
 103 765
 107 779
 109 782
 113 742
 127 795

i.e. no primes less than 64 were generated when a bitlength of 7 was specified.

This MAY be what's wanted, but I think the specification of the constructor
is ambiguous.

----------

12 Jul 2001, eval1127@eng -- test results:

1.3.0:
--------

 67 730
 71 807
 73 761
 79 757
 83 779
 89 739
 97 790
 101 755
 103 749
 107 789
 109 742
 113 811
 127 791

1.4 beta (build 65):
--------------------------
 67 759
 71 783
 73 771
 79 750
 83 762
 89 813
 97 752
 101 790
 103 767
 107 770
 109 761
 113 745
 127 777
(Review ID: 127838)
======================================================================