Increasing Java's BigInteger performance

Question

How to increase performance of Java\'s Big Integer?

For example, this factorial program:

import java.math.*;
class Fac {
  public static void main(String         


        

Answer 1

Start with:

import java.math.*;
class Fac {
  public static void main(String[] args) {
    BigInteger i = BigInteger.ONE;
    BigInteger maxValue = BigInteger.valueOf(99999);

    for(BigInteger z=BigInteger.valueOf(2); z.compareTo(maxValue) != 0;) {
      i = i.multiply(z);
      z = z.add(BigInteger.ONE);
    }

    System.out.println( i );
  }
}

.valueOf source

1081    public static BigInteger More ...valueOf(long val) {
1082        // If -MAX_CONSTANT < val < MAX_CONSTANT, return stashed constant
1083        if (val == 0)
1084            return ZERO;
1085        if (val > 0 && val <= MAX_CONSTANT)
1086            return posConst[(int) val];
1087        else if (val < 0 && val >= -MAX_CONSTANT)
1088            return negConst[(int) -val];
1089
1090        return new BigInteger(val);
1091    }

It will create a new BigInteger everytime since MAX_CONSTANT is 16.

---

I think it could go slower because the GC starts to collect some older BigInteger instances but anyway you should always use int and long.. here BigInteger is not really needed.

After your last test i think we can be sure it could be caused by the GC.