Failing Numerical Methods algorithm

randfortran.f

      PROGRAM RAND2
      IMPLICIT NONE
      REAL R
      REAL ran2
      
      R=ran2(65000)
      WRITE(*,310) R
 310  FORMAT(F6.6)

      STOP
      END

      REAL FUNCTION ran2(idum)
      IMPLICIT NONE
      INTEGER idum,IM1,IM2,IMM1,IA1,IA2,IQ1,IQ2,IR1,IR2,NTAB,NDIV
      REAL ran2,AM,EPS,RNMX
      PARAMETER (IM1=2147483563,IM2=2147483399,
     +     AM=1./IM1,IMM1=IM1-1, IA1=40014,IA2=40692,IQ1=53668,
     +     IQ2=52774,IR1=12211, IR2=3791,NTAB=32,NDIV=1+IMM1/NTAB,
     +     EPS=1.2e-7,RNMX=1.-EPS)

      INTEGER idum2,j,k,iv(NTAB),iy
      SAVE iv,iy,idum2
      DATA idum2/123456789/, iv/NTAB*0/, iy/0/


      if (idum.le.0) then 
         idum=max(-idum,1)
         idum2=idum
         do j=NTAB+8,1,-1
            k=idum/IQ1
            idum=IA1*(idum-k*IQ1)-k*IR1
            if (idum.lt.0) idum=idum+IM1
            if (j.le.NTAB) iv(j)=idum
         enddo
         iy=iv(1)
      endif
 
      k=idum/IQ1
      WRITE(*,310) "IA1:",IA1," idum:", idum, " k:", k, " IQ1:",
     +     IQ1, " IR1", IR1
 310  FORMAT(A, I10, A, I10, A, I10, A, I10, A, I10)
      idum=(IA1*(idum-k*IQ1))-(k*IR1)
      WRITE(*,320) "CRASH JERE\n"
 320  FORMAT(A)
      if (idum.lt.0) idum=idum+IM1

      k=idum2/IQ2
      idum2=IA2*(idum2-k*IQ2)-k*IR2 

      if (idum2.lt.0) idum2=idum2+IM2 
      j=1+iy/NDIV
      iy=iv(j)-idum2
      iv(j)=idum
      if(iy.lt.1)iy=iy+IMM1
      ran2=min(AM*iy,RNMX)
      return
      END