kqsort.f File Reference

Go to the source code of this file.

Functions/Subroutines
subroutine	kqsort (compf, ORD, N)

Function/Subroutine Documentation

kqsort()

subroutine kqsort	(	external	compf,
		dimension(n)	ORD,
			N
	)

Definition at line 198 of file kqsort.f.

References i, n, p, x, y, and z.

!
!==============SORTS THE ARRAY A(I),I=1,2,...,N BY PUTTING THE
!   ASCENDING ORDER VECTOR IN ORD.  THAT IS ASCENDING ORDERED A
!   IS A(ORD(I)),I=1,2,...,N; DESCENDING ORDER A IS A(ORD(N-I+1)),
!   I=1,2,...,N .  THIS SORT RUNS IN TIME PROPORTIONAL TO N LOG N .
!
!
!     ACM QUICKSORT - ALGORITHM #402 - IMPLEMENTED IN FORTRAN BY
!                                 WILLIAM H. VERITY
!                                 COMPUTATION CENTER
!                                 PENNSYLVANIA STATE UNIVERSITY
!                                 UNIVERSITY PARK, PA.  16802
!
      IMPLICIT INTEGER (A-Z)
!
      dimension ord(n),poplst(2,20)
      external compf
!c      INTEGER X,XX,Z,ZZ,Y
!c      CHARACTER *(*) A(N)
!
      ndeep=0
      u1=n
      l1=1
      DO 1  i=1,n
    1 ord(i)=i
    2 IF (u1.GT.l1) GO TO 3
      RETURN
!
    3 l=l1
      u=u1
!
! PART
!
    4 p=l
      q=u
      x=ord(p)
      z=ord(q)

!      IF (A(X).LE.A(Z)) GO TO 5
      if( compf(x, z) .le. 0 ) goto 5 
      y=x
      x=z
      z=y
      yp=ord(p)
      ord(p)=ord(q)
      ord(q)=yp
    5 IF (u-l.LE.1) GO TO 15
      xx=x
      ix=p
      zz=z
      iz=q
!
! LEFT
!
    6 p=p+1
      IF (p.GE.q) GO TO 7
      x=ord(p)
!      IF (A(X).GE.A(XX)) GO TO 8
      if( compf(x, xx) .ge. 0) goto 8
      GO TO 6
    7 p=q-1
      GO TO 13
!
! RIGHT
!
    8 q=q-1
      IF (q.LE.p) GO TO 9
      z=ord(q)
!      IF (A(Z).LE.A(ZZ)) GO TO 10
      if( compf(z, zz) .le. 0)   goto 10
      GO TO 8
    9 q=p
      p=p-1
      z=x
      x=ord(p)
!
! DIST
!
!   10 IF (A(X).LE.A(Z)) GO TO 11
 10   IF ( compf(x, z) .le. 0) goto 11  
      y=x
      x=z
      z=y
      ip=ord(p)
      ord(p)=ord(q)
      ord(q)=ip
!   11 IF (A(X).LE.A(XX)) GO TO 12
   11 IF ( compf( x, xx) .le. 0) goto 12
      xx=x
      ix=p
!   12 IF (A(Z).GE.A(ZZ)) GO TO 6
   12 IF ( compf(z, zz) .ge. 0) goto 6
      zz=z
      iz=q
      GO TO 6
!
! OUT
!
   13 CONTINUE
!      IF (.NOT.(P.NE.IX.AND.A(X).NE.A(XX))) GO TO 14
      IF (.NOT.(p.NE.ix.AND. compf(x, xx) .ne. 0) ) goto 14
      ip=ord(p)
      ord(p)=ord(ix)
      ord(ix)=ip
   14 CONTINUE
!      IF (.NOT.(Q.NE.IZ.AND.A(Z).NE.A(ZZ))) GO TO 15
      IF (.NOT.(q.NE.iz.AND. compf(z, zz) .ne. 0) ) goto 15
      iq=ord(q)
      ord(q)=ord(iz)
      ord(iz)=iq
   15 CONTINUE
      IF (u-q.LE.p-l) GO TO 16
      l1=l
      u1=p-1
      l=q+1
      GO TO 17
   16 u1=u
      l1=q+1
      u=p-1
   17 CONTINUE
      IF (u1.LE.l1) GO TO 18
!
! START RECURSIVE CALL
!
      ndeep=ndeep+1
      poplst(1,ndeep)=u
      poplst(2,ndeep)=l
      GO TO 3
   18 IF (u.GT.l) GO TO 4
!
! POP BACK UP IN THE RECURSION LIST
!
      IF (ndeep.EQ.0) GO TO 2
      u=poplst(1,ndeep)
      l=poplst(2,ndeep)
      ndeep=ndeep-1
      GO TO 18
!
! END SORT
! END QSORT
!