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The Laws of Cryptography with Java Code.

Program with a formula for channel capacity:

// Cap.java: calculate channel capacity, binary symmetric channel
//   p: the channel probability for a binary symmetric channel
public class Cap {

   // main function to do calculation
   public static void main (String[] args) {
      double p = (Double.valueOf(args[0])).doubleValue(); // channel probability
      System.out.println("Probability: " + p +
          ", Capacity: " + capacity(p));
   } // end of main

   // capacity: the capacity of the binary symmetric channel
   private static double capacity(double p) {
      if (p == 0 || p == 1) return 1;
      return 1 + p*log2(p) + (1 - p)*log2(1 - p);
   }

   // log2:  Logarithm base 2
   public static double log2(double d) {
      return Math.log(d)/Math.log(2.0);
   }

}

Typical output:

% javac Cap.java
% java Cap 0.3
Probability: 0.3, Capacity: 0.11870910076930735
% java Cap 0.999
Probability: 0.999, Capacity: 0.9885922422625388
% java Cap 0.001
Probability: 0.0010, Capacity: 0.9885922422625388
% java Cap 0.5
Probability: 0.5, Capacity: 0.0
% java Cap 0.5001
Probability: 0.5001, Capacity: 2.8853901046232977E-8
% java Cap 0.51
Probability: 0.51, Capacity: 2.8855824719009604E-4