/* CSE2304, 2006, Semester 1
   Random Pairs Generator for Prac2+3.

   Compile this code using the following Syntax
   gcc gen.c -o gen -lm
*/

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

void genRanNums( long seed, int nPairs, int nDivisions )
 { double mid, length, left, right;
   int nDivision;
   if( nDivisions < 1 ) nDivisions = 1;
   if( nPairs     < 0 ) nPairs     = 0;
   srand48(seed);  // set the seed of the pseudo-random number generator

   while( nPairs-- )
    { do{ mid = drand48();
          // 0.0 <= m mid < 1.0
          for( nDivision = 0; nDivision < nDivisions-1; nDivision++ )
             if( drand48() < 0.5 ) break;  // nDivision biased to be small
          // nDivision < nDivisions
          length = (nDivision + drand48()) / nDivisions;
          // 0.0 <= length < 1.0,  length is uniformly distributed...
          // ...in [nDivision/nDivisions, (nDivision+1)/nDivisions)
          left = mid-length/2.0, right = mid+length/2.0;
      }while( left >= right ||  left < 0.0 || right > 1.0 );//check limits
      // 0.0 <= left < right <= 1.0
      printf("%f %f\n", left, right);
    }
 }//genRanRums


main(int argc,  char *argv[])
 { if( argc != 4 )
    { printf("gen seed nPairs nLengthDivisions\n");
      printf("e.g.  gen 117 5 3       gives...\n");
      genRanNums(117, 5, 3);
      printf("NB. large nLengthDivisions => small average fragment length\n");
    }
   else
      genRanNums(atol(argv[1]), atoi(argv[2]), atoi(argv[3]));
 }//main

// Available under GNU General Public Licence (GPL) open-source licence.
// L.Allison, Monash University, Melbourne, Vic, .au,  3/2006.