C++*********************************************************************
C
C ACRS_2.F
C              PGI BUG                         FEB 10 2006 ArDean Leith
C              MOD PGI COMPILER BUG            FEB 19 2008 ArDean Leith
C
C **********************************************************************
C=* FROM: SPIDER - MODULAR IMAGE PROCESSING SYSTEM.   AUTHOR: J.FRANK  *
C=* Copyright (C) 1985-2008  Health Research Inc.                      *
C=*                                                                    *
C=* HEALTH RESEARCH INCORPORATED (HRI),                                *   
C=* ONE UNIVERSITY PLACE, RENSSELAER, NY 12144-3455.                   *
C=*                                                                    *
C=* Email:  spider@wadsworth.org                                       *
C=*                                                                    *
C=* This program is free software; you can redistribute it and/or      *
C=* modify it under the terms of the GNU General Public License as     *
C=* published by the Free Software Foundation; either version 2 of the *
C=* License, or (at your option) any later version.                    *
C=*                                                                    *
C=* This program is distributed in the hope that it will be useful,    *
C=* but WITHOUT ANY WARRANTY; without even the implied warranty of     *
C=* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  *
C=* General Public License for more details.                           *
C=*                                                                    *
C=* You should have received a copy of the GNU General Public License  *
C=* along with this program; if not, write to the                      *
C=* Free Software Foundation, Inc.,                                    *
C=* 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.      *
C=*                                                                    *
C **********************************************************************
C
C  Calculates circular autocorrelation, non-power-of-two dimensions
C  Input - X Fourier transform
C  Output -  O=F(X*conjg(X))
C  
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C--*********************************************************************

        SUBROUTINE ACRS_2(X,O, LS,NSAM,NROW)

        COMPLEX          :: X(LS/2,NROW)
        COMPLEX          :: O(LS/2,NROW)

        DOUBLE PRECISION :: PI2
        COMPLEX          :: CTEMP

        NNNN = LS/2

        PI2  = 8.0*DATAN(1.0D0)
        ITMP = NSAM/2
        SX   = PI2*FLOAT(ITMP)/FLOAT(NSAM)
        ITMP = NROW/2
        SY   = PI2*FLOAT(ITMP)/FLOAT(NROW)

c$omp   parallel do private(i,j,ix,iy,argy,arg,ctemp)
        DO J=1,NROW
           IY = J-1
           IF (IY .GT. NROW/2)  IY = IY-NROW
           ARGY = SY * IY

           DO I=1,NNNN
              IX     = I - 1
              ARG    = SX * IX + ARGY
              CTEMP  = CMPLX(COS(ARG),SIN(ARG))
              O(I,J) = X(I,J) * CONJG(X(I,J)) * CTEMP
           ENDDO
        ENDDO   

        INS = -1
        CALL FMRS_2(O,NSAM,NROW,INS)

        END