!!  Copyright (C)  Stichting Deltares, 2012-2020.
!!
!!  This program is free software: you can redistribute it and/or modify
!!  it under the terms of the GNU General Public License version 3,
!!  as published by the Free Software Foundation.
!!
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!!  but WITHOUT ANY WARRANTY; without even the implied warranty of
!!  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
!!  GNU General Public License for more details.
!!
!!  You should have received a copy of the GNU General Public License
!!  along with this program. If not, see <http://www.gnu.org/licenses/>.
!!
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!!  of Stichting Deltares remain the property of Stichting Deltares. All
!!  rights reserved.

      subroutine srot (n,sx,incx,sy,incy,c,s)
!
!     applies a plane rotation.
!     jack dongarra, linpack, 3/11/78.
!
      use timers

      real(8) sx(1),sy(1),stemp,c,s
      integer i,incx,incy,ix,iy,n
      integer(4) ithandl /0/
      if ( timon ) call timstrt ( "srot", ithandl )
!
      if(n.le.0)return
      if(incx.eq.1.and.incy.eq.1)go to 20
!
!       code for unequal increments or equal increments not equal
!         to 1
!
      ix = 1
      iy = 1
      if(incx.lt.0)ix = (-n+1)*incx + 1
      if(incy.lt.0)iy = (-n+1)*incy + 1
      do 10 i = 1,n
        stemp = c*sx(ix) + s*sy(iy)
        sy(iy) = c*sy(iy) - s*sx(ix)
        sx(ix) = stemp
        ix = ix + incx
        iy = iy + incy
   10 continue
      goto 9999  !   return
!
!       code for both increments equal to 1
!
   20 do 30 i = 1,n
        stemp = c*sx(i) + s*sy(i)
        sy(i) = c*sy(i) - s*sx(i)
        sx(i) = stemp
   30 continue
 9999 if ( timon ) call timstop ( ithandl )
      return
      end