/*
 * UCF, CS, Erik Reinhard, Oct 15, 2003
 *
 * Radix sort algorithm
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

#define DEBUG           1        /* Set this to 1 to see extra print statements  */
#define MAX_VALUE      32        /* Maximum value in array, just to comput #bits */
#define N              16        /* Number of elements in array                  */

unsigned int A[N];

void print ()
{
  int i;

  fprintf (stderr, "\nArray: ");
  for (i = 0; i < N; i++)
    fprintf (stderr, "%i  ", A[i]);
  fprintf (stderr, "\n\n");
}

void swap (int i, int j)
{
  unsigned int value;

  value = A[i];
  A[i]  = A[j];
  A[j]  = value;
}

int partition (int start, int end, int bit)
{
  int i = start;
  int j = end;

  while (i < j)
  {
    while ((i < end) && !(A[i] & (1 << bit)))
      i++;
    while ((j >= i) && (A[j] & (1 << bit)))
      j--;
    if (i < j)
      swap (i, j);
  }

  // Output for debugging purposes

#if DEBUG
  fprintf (stderr, "Bit %i (%i %i)\t%i:\t ", bit, start, end, j);
  for (i = 0; i < N; i++)
    if ((i < start) || (i > end))
      fprintf (stderr, "_ ");
    else
      fprintf (stderr, "%i ", (A[i] & (1 << bit)) > 0);
  fprintf (stderr, "   ");
  for (i = 0; i < N; i++)
      fprintf (stderr, "%i ", A[i]);
  fprintf (stderr, "\n");
#endif

  return j;
}

void radix_sort (int start, int end, int bit)
{
  if (bit >= 0)
  {
    int split = partition (start, end, bit);
    if (start < split)
      radix_sort (start, split, bit-1);
    if (split < end)
      radix_sort (split+1, end, bit-1);
  }
}

int main ()
{
  int i;
  int max_bits = 0;

  // Randomize array

  for (i = 0; i < N; i++)
    A[i] = drand48() * MAX_VALUE;
  print ();

  // Compute how many bits we need to sort

  i = MAX_VALUE;              //  Maximum value of elements in array
  while (i >>= 1)             //  Divide by 2
    max_bits++;               //  Increase number of bits

#if DEBUG
  fprintf (stderr, "Bit (start, end) split:  bit_values  array_values\n\n"); 
#endif

  // Sort array

  radix_sort (0, N-1, max_bits);

  // Print array

  print ();

#if DEBUG
  fprintf (stderr, "max bits = %i\n", max_bits);
#endif

  return 0;
}