/* ran.c - uniform random number generator in [0, 1) */#define  a    16807                              /* that is, \(a = 7\sp{5}\) */#define  m    2147483647                         /* that is, \(m = 2\sp{31}-1\) */#define  q    127773                             /* note, \(q = m/a\) = quotient */#define  r    2836                               /* note, \(r = m\%a\) = remainder */double ran(iseed)                                /* usage: u = ran(&iseed); */long *iseed;                                     /* iseed passed by address */{    *iseed = a * (*iseed % q) - r * (*iseed / q);          /* update seed */    if (*iseed < 0)                              /* wrap to positive values */           *iseed += m;    return (double) *iseed / (double) m;}