ran1.f90

module random
  private idum, IA, IM,IQ,IR,NTAB,NDIV
  private ran1,AM,EPS,RNMX
  private j,k,iv,iy
  !
  INTEGER*4 idum,IA,IM,IQ,IR,NTAB,NDIV
  REAL*8 ran1,AM,EPS,RNMX
  PARAMETER (IA=16807,IM=2147483647,AM=1./IM,IQ=127773,IR=2836,  &
  NTAB=32,NDIV=1+(IM-1)/NTAB,EPS=1.2e-7,RNMX=1.-EPS)
  INTEGER j,k,iv(NTAB),iy

Contains

FUNCTION ran1(idum)


SAVE iv,iy
!SAVE
DATA iv /NTAB*0/, iy /0/
if (idum.le.0.or.iy.eq.0) then
idum=max(-idum,1)
do 11 j=NTAB+8,1,-1
k=idum/IQ
idum=IA*(idum-k*IQ)-IR*k
if (idum.lt.0) idum=idum+IM
if (j.le.NTAB) iv(j)=idum
11      continue
iy=iv(1)
endif
k=idum/IQ
idum=IA*(idum-k*IQ)-IR*k
if (idum.lt.0) idum=idum+IM

j=1+iy/NDIV
iy=iv(j)
iv(j)=idum
ran1=min(AM*iy,RNMX)
return
END FUNCTION ran1