Use ran1 FORTRAN 77 subroutine in FORTRAN 90 - random

Question

I am trying to use ran1 from Numerical Recipes in my FORTRAN 90 code. I think a common way is to compile the old subroutine separately, then use the object file. But here I want to know what change is necessary to use it directly in my code.
FUNCTION ran1(idum)
INTEGER idum,IA,IM,IQ,IR,NTAB,NDIV
REAL 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)
! “Minimal” random number generator of Park and Miller with Bays-Durham shuffle and
! added safeguards. Returns a uniform random deviate between 0.0 and 1.0 (exclusive of
! the endpoint values). Call with idum a negative integer to initialize; thereafter, do not
! alter idum between successive deviates in a sequence. RNMX should approximate the largest
! floating value that is less than 1.
INTEGER j,k,iv(NTAB),iy
SAVE iv,iy
DATA iv /NTAB*0/, iy /0/
iy = 0
if (idum.le.0.or.iy.eq.0) then !Initialize.
idum=max(-idum,1)
! Be sure to prevent idum = 0.
do 11 j=NTAB+8,1,-1
! Load the shuffle table (after 8 warm-ups).
k=idum/IQ
idum=IA*(idum-k*IQ)-IR*k
if (idum.lt.0) idum=idum+IM
if (j.le.NTAB) iv(j)=idum! Compute idum=mod(IA*idum,IM) without overflows by
enddo 11
iy=iv(1)
endif
k=idum/IQ
idum=IA*(idum-k*IQ)-IR*k
! Compute idum=mod(IA*idum,IM) without overflows by
if (idum.lt.0) idum=idum+IM ! Schrage’s method.
j=1+iy/NDIV
iy=iv(j) ! Output previously stored value and refill the shuffle table.
iv(j)=idum
ran1=min(AM*iy,RNMX) ! Because users don’t expect endpoint values.
return
END

Answer 1

Your code is malformed. It looks like you copied it manually from the book, but not exactly. The second problem is actually present even in the book.
Firstly, there should be a line continuation and not a comment in the parameter statement on the second and third line
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)
(converted to free form, see the book for the original)
Secondly, the loop is a strange combination of a do loop with numeric label and a do loop with end do:
do 11 j=NTAB+8,1,-1
...
enddo 11
should be
do j=NTAB+8,1,-1
...
enddo
or
do 11 j=NTAB+8,1,-1
...
11 continue
There may be more problems present.