// ----------------------------------------------------------------------
// 
//  Module:          perm_gen.cc
//  Description:     constructs a random key for permutation of characters.
//                   Allowed characters are upper case and punctuation. 
//  Contributed by:  Rene Peralta
//  Date:            2002
//  Modified by:     Michael Fischer
//  Date:            2005
//  
// ----------------------------------------------------------------------

#define ASCII_SIZE 256
#define LOW_INDEX 32
#define HIGH_INDEX 126
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <ctype.h>

using namespace std;

extern "C" void srand(unsigned int seed);
extern "C" int rand();
void permute(int L[], int l, int h); // permutes the elements of L[l..h]
int randint(int u); // returns a random integer in the range 0..u-1

ofstream out_file("KEY");

int
main( int argc, char *argv[ ] )
{
    int key[ASCII_SIZE];
    int plain[ASCII_SIZE];
    int i,j;
    unsigned int seed;

    // get seed for random number generator . WARNING toy C generator

    cout << "enter seed " << endl;
    cin >> seed ;
    srand(seed);
    
    // fill the key array with the numbers to be permuted
    for (int i=LOW_INDEX; i <= HIGH_INDEX; i++) 
    {
      plain[i] = i;
      key[i] = i;
    }
    // permute
    permute(key,LOW_INDEX,HIGH_INDEX);
    
    // output key
    for (int i = LOW_INDEX; i <= HIGH_INDEX; i++) 
     out_file << plain[i] << " " << key[i] << endl;

    out_file << -1 << endl; // -1 is end-of-list

}

void permute(int L[], int l, int h) // permutes the elements of L[l..h]
{
  if (l == h) return; // base case
  // exchange L[l] with a random element in L
  int hit = l + randint(h-l+1);
  
  int aux = L[hit];
  L[hit] = L[l];
  L[l] = aux;
  l++;
  permute(L,l,h);
}


int randint(int u) // in the range 0..u-1
{
  int r = rand();
  if (r < 0) r = -r;
  // cout << "randint(" << u << ") returning " << r % u << endl;
  return (r % u);
}