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module isort
contains
  subroutine  qsorti(ord,N,A)
    implicit none
#ifdef LONGLONG
    include 'precision_longlong.inc'
#else
    include 'precision.inc'
#endif
    integer(kind=kint) :: N
    integer(kind=kint),DIMENSION(N) ::ORD
    integer(kind=kint),DIMENSION(N) ::A

    integer(kind=kint) :: i
    DO i=1,N
       ord(i)=i
    END DO
    call qsort_rec(ord,N,A,1,N)
    contains

      recursive subroutine qsort_rec(ord,N,A,l,h)
        implicit none
#ifdef LONGLONG
    include 'precision_longlong.inc'
#else
    include 'precision.inc'
#endif
        integer(kind=kint) :: N,l,h
        integer(kind=kint),DIMENSION(N) ::ORD
        integer(kind=kint),DIMENSION(N) ::A

        integer(kind=kint) :: ii,jj,i,j,k,p,temp,t

        if(l>=h) return

        p=(l+h)/2
        temp=ord(p);ord(p)=ord(l);ord(l)=temp;
        t=A(temp);i=l;j=h;

        DO
           DO ii=i+1,h
              k=ord(ii)
              if(A(k)>=t) exit
           END DO
           i=ii
           DO jj=j,l+1,-1
              k=ord(jj)
              if(A(k)<t) exit
           END DO
           j=jj

           if(i>j) exit
           temp=ord(i);ord(i)=ord(j);ord(j)=temp;
        END DO
        temp=ord(l);ord(l)=ord(j);ord(j)=temp;

        call qsort_rec(ord,N,A,l,j-1)
        call qsort_rec(ord,N,A,j+1,h)
      end subroutine qsort_rec
      
  end subroutine qsorti
end module isort









