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fft_generic.f90
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fft_generic.f90
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!=======================================================================
! This is part of the 2DECOMP&FFT library
!
! 2DECOMP&FFT is a software framework for general-purpose 2D (pencil)
! decomposition. It also implements a highly scalable distributed
! three-dimensional Fast Fourier Transform (FFT).
!
! Copyright (C) 2009-2011 Ning Li, the Numerical Algorithms Group (NAG)
!
!=======================================================================
! This is the 'generic' implementation of the FFT library
module decomp_2d_fft
use decomp_2d ! 2D decomposition module
use glassman
implicit none
private ! Make everything private unless declared public
! engine-specific global variables
complex(mytype), allocatable, dimension(:) :: buf, scratch
! common code used for all engines, including global variables,
! generic interface definitions and several subroutines
#include "fft_common.f90"
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! This routine performs one-time initialisations for the FFT engine
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
subroutine init_fft_engine
implicit none
integer :: cbuf_size
if (nrank==0) then
write(*,*) ' '
write(*,*) '***** Using the generic FFT engine *****'
write(*,*) ' '
end if
cbuf_size = max(ph%xsz(1), ph%ysz(2))
cbuf_size = max(cbuf_size, ph%zsz(3))
allocate(buf(cbuf_size))
allocate(scratch(cbuf_size))
return
end subroutine init_fft_engine
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! This routine performs one-time finalisations for the FFT engine
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
subroutine finalize_fft_engine
implicit none
deallocate(buf,scratch)
return
end subroutine finalize_fft_engine
! Following routines calculate multiple one-dimensional FFTs to form
! the basis of three-dimensional FFTs.
! c2c transform, multiple 1D FFTs in x direction
subroutine c2c_1m_x(inout, isign, decomp)
implicit none
complex(mytype), dimension(:,:,:), intent(INOUT) :: inout
integer, intent(IN) :: isign
TYPE(DECOMP_INFO), intent(IN) :: decomp
integer :: i,j,k
do k=1,decomp%xsz(3)
do j=1,decomp%xsz(2)
do i=1,decomp%xsz(1)
buf(i) = inout(i,j,k)
end do
call spcfft(buf,decomp%xsz(1),isign,scratch)
do i=1,decomp%xsz(1)
inout(i,j,k) = buf(i)
end do
end do
end do
return
end subroutine c2c_1m_x
! c2c transform, multiple 1D FFTs in y direction
subroutine c2c_1m_y(inout, isign, decomp)
implicit none
complex(mytype), dimension(:,:,:), intent(INOUT) :: inout
integer, intent(IN) :: isign
TYPE(DECOMP_INFO), intent(IN) :: decomp
integer :: i,j,k
do k=1,decomp%ysz(3)
do i=1,decomp%ysz(1)
do j=1,decomp%ysz(2)
buf(j) = inout(i,j,k)
end do
call spcfft(buf,decomp%ysz(2),isign,scratch)
do j=1,decomp%ysz(2)
inout(i,j,k) = buf(j)
end do
end do
end do
return
end subroutine c2c_1m_y
! c2c transform, multiple 1D FFTs in z direction
subroutine c2c_1m_z(inout, isign, decomp)
implicit none
complex(mytype), dimension(:,:,:), intent(INOUT) :: inout
integer, intent(IN) :: isign
TYPE(DECOMP_INFO), intent(IN) :: decomp
integer :: i,j,k
do j=1,decomp%zsz(2)
do i=1,decomp%zsz(1)
do k=1,decomp%zsz(3)
buf(k) = inout(i,j,k)
end do
call spcfft(buf,decomp%zsz(3),isign,scratch)
do k=1,decomp%zsz(3)
inout(i,j,k) = buf(k)
end do
end do
end do
return
end subroutine c2c_1m_z
! r2c transform, multiple 1D FFTs in x direction
subroutine r2c_1m_x(input, output)
implicit none
real(mytype), dimension(:,:,:), intent(IN) :: input
complex(mytype), dimension(:,:,:), intent(OUT) :: output
integer :: i,j,k, s1,s2,s3, d1
s1 = size(input,1)
s2 = size(input,2)
s3 = size(input,3)
d1 = size(output,1)
do k=1,s3
do j=1,s2
! Glassman's FFT is c2c only,
! needing some pre- and post-processing for r2c
! pack real input in complex storage
do i=1,s1
buf(i) = cmplx(input(i,j,k),0._mytype, kind=mytype)
end do
call spcfft(buf,s1,-1,scratch)
! note d1 ~ s1/2+1
! simply drop the redundant part of the complex output
do i=1,d1
output(i,j,k) = buf(i)
end do
end do
end do
return
end subroutine r2c_1m_x
! r2c transform, multiple 1D FFTs in z direction
subroutine r2c_1m_z(input, output)
implicit none
real(mytype), dimension(:,:,:), intent(IN) :: input
complex(mytype), dimension(:,:,:), intent(OUT) :: output
integer :: i,j,k, s1,s2,s3, d3
s1 = size(input,1)
s2 = size(input,2)
s3 = size(input,3)
d3 = size(output,3)
do j=1,s2
do i=1,s1
! Glassman's FFT is c2c only,
! needing some pre- and post-processing for r2c
! pack real input in complex storage
do k=1,s3
buf(k) = cmplx(input(i,j,k),0._mytype, kind=mytype)
end do
call spcfft(buf,s3,-1,scratch)
! note d3 ~ s3/2+1
! simply drop the redundant part of the complex output
do k=1,d3
output(i,j,k) = buf(k)
end do
end do
end do
return
end subroutine r2c_1m_z
! c2r transform, multiple 1D FFTs in x direction
subroutine c2r_1m_x(input, output)
implicit none
complex(mytype), dimension(:,:,:), intent(IN) :: input
real(mytype), dimension(:,:,:), intent(OUT) :: output
integer :: i,j,k, d1,d2,d3
d1 = size(output,1)
d2 = size(output,2)
d3 = size(output,3)
do k=1,d3
do j=1,d2
! Glassman's FFT is c2c only,
! needing some pre- and post-processing for c2r
do i=1,d1/2+1
buf(i) = input(i,j,k)
end do
! expanding to a full-size complex array
! For odd N, the storage is:
! 1, 2, ...... N/2+1 integer division rounded down
! N, ...... N/2+2 => a(i) is conjugate of a(N+2-i)
! For even N, the storage is:
! 1, 2, ...... N/2 , N/2+1
! N, ...... N/2+2 again a(i) conjugate of a(N+2-i)
do i=d1/2+2,d1
buf(i) = conjg(buf(d1+2-i))
end do
call spcfft(buf,d1,1,scratch)
do i=1,d1
! simply drop imaginary part
output(i,j,k) = real(buf(i), kind=mytype)
end do
end do
end do
return
end subroutine c2r_1m_x
! c2r transform, multiple 1D FFTs in z direction
subroutine c2r_1m_z(input, output)
implicit none
complex(mytype), dimension(:,:,:), intent(IN) :: input
real(mytype), dimension(:,:,:), intent(OUT) :: output
integer :: i,j,k, d1,d2,d3
d1 = size(output,1)
d2 = size(output,2)
d3 = size(output,3)
do j=1,d2
do i=1,d1
do k=1,d3/2+1
buf(k) = input(i,j,k)
end do
do k=d3/2+2,d3
buf(k) = conjg(buf(d3+2-k))
end do
call spcfft(buf,d3,1,scratch)
do k=1,d3
output(i,j,k) = real(buf(k), kind=mytype)
end do
end do
end do
return
end subroutine c2r_1m_z
#include "fft_common_3d.f90"
end module decomp_2d_fft