random number generator in c

/********************************************************************************** * Author : Saurabh Gupta * Modified : 09 September 2011 * Description : Function to return random number on the interval 0 to 1. * Usage : y = randNew(0); [normal] or y = randNew(-1); [ to reset]. * * Note : Random initally takes any negative number (idum) and returns a random number on the interval 0 to 1. *********************************************************************************/ #include <stdio.h> #include <math.h> #include <stddef.h> #include <stdlib.h> #include "randNew.h" /* * add function signature to your code header file. */ double randNew(int); double randNew(int reset) { /* constants for random number generator */ #define M1 259200 #define IA1 7141 #define IC1 54773 #define M2 134456 #define IA2 8121 #define IC2 28411 #define M3 243000 #define IA3 4561 #define IC3 51349 int j; static int idum = -7141; static int iff = 0; static long int ix1, ix2, ix3; double RM1, RM2, temp; static double r[97]; /* periodically re-set random number generator */ if (reset) { idum = -7141; } RM1 = 1.0/M1; RM2 = 1.0/M2; if(idum < 0 || iff == 0) /* initialise on first call */ { iff = 1; ix1 = (IC1 - (idum)) % M1; /* seeding routines */ ix1 = (IA1 *ix1 + IC1) % M1; ix2 = ix1 % M2; ix1 = (IA1 * ix1 + IC1) % M1; ix3 = ix1 % M3; for (j = 0; j < 97; j++) { ix1 = (IA1 * ix1 + IC1) % M1; ix2 = (IA2 * ix2 + IC2) % M2; r[j] = (ix1 + ix2 * RM2) * RM1; } idum = 1; } /* * generate next number for each sequence */ ix1 = (IA1 * ix1 + IC1) % M1; ix2 = (IA2 * ix2 + IC2) % M2; ix3 = (IA3 * ix3 + IC3) % M3; /* * randomly sample r vector */ j = 0 + ((96 * ix3) / M3); if (j > 96 || j < 0) { printf("Error in random number generator\n"); } temp = r[j]; /* * replace r[j] with next value in the sequence */ r[j] = (ix1 + ix2 * RM2) * RM1; return temp; }