fft8g.f

This is a package to calculate Discrete Fourier/Cosine/Sine Transforms of 1-dimensional sequences of

      if (isgn .lt. 0) then
          xr = a(n - 1)
          do j = n - 2, 2, -2
              a(j + 1) = -a(j) - a(j - 1)
              a(j) = a(j) - a(j - 1)
          end do
          a(1) = a(0) + xr
          a(0) = a(0) - xr
          if (n .gt. 4) then
              call rftbsub(n, a, nc, w(nw))
              call bitrv2(n, ip(2), a)
              call cftbsub(n, a, w)
          else if (n .eq. 4) then
              call cftfsub(n, a, w)
          end if
      end if
      call dstsub(n, a, nc, w(nw))
      if (isgn .ge. 0) then
          if (n .gt. 4) then
              call bitrv2(n, ip(2), a)
              call cftfsub(n, a, w)
              call rftfsub(n, a, nc, w(nw))
          else if (n .eq. 4) then
              call cftfsub(n, a, w)
          end if
          xr = a(0) - a(1)
          a(0) = a(0) + a(1)
          do j = 2, n - 2, 2
              a(j - 1) = -a(j) - a(j + 1)
              a(j) = a(j) - a(j + 1)
          end do
          a(n - 1) = -xr
      end if
      end
!
      subroutine dfct(n, a, t, ip, w)
      integer n, ip(0 : *), j, k, l, m, mh, nw, nc
      real*8 a(0 : n), t(0 : n / 2), w(0 : *), xr, xi, yr, yi
      nw = ip(0)
      if (n .gt. 8 * nw) then
          nw = n / 8
          call makewt(nw, ip, w)
      end if
      nc = ip(1)
      if (n .gt. 2 * nc) then
          nc = n / 2
          call makect(nc, ip, w(nw))
      end if
      m = n / 2
      yi = a(m)
      xi = a(0) + a(n)
      a(0) = a(0) - a(n)
      t(0) = xi - yi
      t(m) = xi + yi
      if (n .gt. 2) then
          mh = m / 2
          do j = 1, mh - 1
              k = m - j
              xr = a(j) - a(n - j)
              xi = a(j) + a(n - j)
              yr = a(k) - a(n - k)
              yi = a(k) + a(n - k)
              a(j) = xr
              a(k) = yr
              t(j) = xi - yi
              t(k) = xi + yi
          end do
          t(mh) = a(mh) + a(n - mh)
          a(mh) = a(mh) - a(n - mh)
          call dctsub(m, a, nc, w(nw))
          if (m .gt. 4) then
              call bitrv2(m, ip(2), a)
              call cftfsub(m, a, w)
              call rftfsub(m, a, nc, w(nw))
          else if (m .eq. 4) then
              call cftfsub(m, a, w)
          end if
          a(n - 1) = a(0) - a(1)
          a(1) = a(0) + a(1)
          do j = m - 2, 2, -2
              a(2 * j + 1) = a(j) + a(j + 1)
              a(2 * j - 1) = a(j) - a(j + 1)
          end do
          l = 2
          m = mh
          do while (m .ge. 2)
              call dctsub(m, t, nc, w(nw))
              if (m .gt. 4) then
                  call bitrv2(m, ip(2), t)
                  call cftfsub(m, t, w)
                  call rftfsub(m, t, nc, w(nw))
              else if (m .eq. 4) then
                  call cftfsub(m, t, w)
              end if
              a(n - l) = t(0) - t(1)
              a(l) = t(0) + t(1)
              k = 0
              do j = 2, m - 2, 2
                  k = k + 4 * l
                  a(k - l) = t(j) - t(j + 1)
                  a(k + l) = t(j) + t(j + 1)
              end do
              l = 2 * l
              mh = m / 2
              do j = 0, mh - 1
                  k = m - j
                  t(j) = t(m + k) - t(m + j)
                  t(k) = t(m + k) + t(m + j)
              end do
              t(mh) = t(m + mh)
              m = mh
          end do
          a(l) = t(0)
          a(n) = t(2) - t(1)
          a(0) = t(2) + t(1)
      else
          a(1) = a(0)
          a(2) = t(0)
          a(0) = t(1)
      end if
      end
!
      subroutine dfst(n, a, t, ip, w)
      integer n, ip(0 : *), j, k, l, m, mh, nw, nc
      real*8 a(0 : n - 1), t(0 : n / 2 - 1), w(0 : *), xr, xi, yr, yi
      nw = ip(0)
      if (n .gt. 8 * nw) then
          nw = n / 8
          call makewt(nw, ip, w)
      end if
      nc = ip(1)
      if (n .gt. 2 * nc) then
          nc = n / 2
          call makect(nc, ip, w(nw))
      end if
      if (n .gt. 2) then
          m = n / 2
          mh = m / 2
          do j = 1, mh - 1
              k = m - j
              xr = a(j) + a(n - j)
              xi = a(j) - a(n - j)
              yr = a(k) + a(n - k)
              yi = a(k) - a(n - k)
              a(j) = xr
              a(k) = yr
              t(j) = xi + yi
              t(k) = xi - yi
          end do
          t(0) = a(mh) - a(n - mh)
          a(mh) = a(mh) + a(n - mh)
          a(0) = a(m)
          call dstsub(m, a, nc, w(nw))
          if (m .gt. 4) then
              call bitrv2(m, ip(2), a)
              call cftfsub(m, a, w)
              call rftfsub(m, a, nc, w(nw))
          else if (m .eq. 4) then
              call cftfsub(m, a, w)
          end if
          a(n - 1) = a(1) - a(0)
          a(1) = a(0) + a(1)
          do j = m - 2, 2, -2
              a(2 * j + 1) = a(j) - a(j + 1)
              a(2 * j - 1) = -a(j) - a(j + 1)
          end do
          l = 2
          m = mh
          do while (m .ge. 2)
              call dstsub(m, t, nc, w(nw))
              if (m .gt. 4) then
                  call bitrv2(m, ip(2), t)
                  call cftfsub(m, t, w)
                  call rftfsub(m, t, nc, w(nw))
              else if (m .eq. 4) then
                  call cftfsub(m, t, w)
              end if
              a(n - l) = t(1) - t(0)
              a(l) = t(0) + t(1)
              k = 0
              do j = 2, m - 2, 2
                  k = k + 4 * l
                  a(k - l) = -t(j) - t(j + 1)
                  a(k + l) = t(j) - t(j + 1)
              end do
              l = 2 * l
              mh = m / 2
              do j = 1, mh - 1
                  k = m - j
                  t(j) = t(m + k) + t(m + j)
                  t(k) = t(m + k) - t(m + j)
              end do
              t(0) = t(m + mh)
              m = mh
          end do
          a(l) = t(0)
      end if
      a(0) = 0
      end
!
! -------- initializing routines --------
!
      subroutine makewt(nw, ip, w)
      integer nw, ip(0 : *), j, nwh
      real*8 w(0 : nw - 1), delta, x, y
      ip(0) = nw
      ip(1) = 1
      if (nw .gt. 2) then
          nwh = nw / 2
          delta = atan(1.0d0) / nwh
          w(0) = 1
          w(1) = 0
          w(nwh) = cos(delta * nwh)
          w(nwh + 1) = w(nwh)
          if (nwh .gt. 2) then
              do j = 2, nwh - 2, 2
                  x = cos(delta * j)
                  y = sin(delta * j)
                  w(j) = x
                  w(j + 1) = y
                  w(nw - j) = y
                  w(nw - j + 1) = x
              end do
              do j = nwh - 2, 2, -2
                  x = w(2 * j)
                  y = w(2 * j + 1)
                  w(nwh + j) = x
                  w(nwh + j + 1) = y
              end do
              call bitrv2(nw, ip(2), w)
          end if
      end if
      end
!
      subroutine makect(nc, ip, c)
      integer nc, ip(0 : *), j, nch
      real*8 c(0 : nc - 1), delta
      ip(1) = nc
      if (nc .gt. 1) then
          nch = nc / 2
          delta = atan(1.0d0) / nch
          c(0) = cos(delta * nch)
          c(nch) = 0.5d0 * c(0)
          do j = 1, nch - 1
              c(j) = 0.5d0 * cos(delta * j)
              c(nc - j) = 0.5d0 * sin(delta * j)
          end do
      end if
      end
!
! -------- child routines --------
!
      subroutine bitrv2(n, ip, a)
      integer n, ip(0 : *), j, j1, k, k1, l, m, m2
      real*8 a(0 : n - 1), xr, xi, yr, yi
      ip(0) = 0
      l = n
      m = 1
      do while (8 * m .lt. l)
          l = l / 2
          do j = 0, m - 1
              ip(m + j) = ip(j) + l
          end do
          m = m * 2
      end do
      m2 = 2 * m
      if (8 * m .eq. l) then
          do k = 0, m - 1
              do j = 0, k - 1
                  j1 = 2 * j + ip(k)
                  k1 = 2 * k + ip(j)
                  xr = a(j1)
                  xi = a(j1 + 1)
                  yr = a(k1)
                  yi = a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
                  j1 = j1 + m2
                  k1 = k1 + 2 * m2
                  xr = a(j1)
                  xi = a(j1 + 1)
                  yr = a(k1)
                  yi = a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
                  j1 = j1 + m2
                  k1 = k1 - m2
                  xr = a(j1)
                  xi = a(j1 + 1)
                  yr = a(k1)
                  yi = a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
                  j1 = j1 + m2
                  k1 = k1 + 2 * m2
                  xr = a(j1)
                  xi = a(j1 + 1)
                  yr = a(k1)
                  yi = a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
              end do
              j1 = 2 * k + m2 + ip(k)
              k1 = j1 + m2
              xr = a(j1)
              xi = a(j1 + 1)
              yr = a(k1)
              yi = a(k1 + 1)
              a(j1) = yr
              a(j1 + 1) = yi
              a(k1) = xr
              a(k1 + 1) = xi
          end do
      else
          do k = 1, m - 1
              do j = 0, k - 1
                  j1 = 2 * j + ip(k)
                  k1 = 2 * k + ip(j)
                  xr = a(j1)
                  xi = a(j1 + 1)
                  yr = a(k1)
                  yi = a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
                  j1 = j1 + m2
                  k1 = k1 + m2
                  xr = a(j1)
                  xi = a(j1 + 1)
                  yr = a(k1)
                  yi = a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
              end do
          end do
      end if
      end
!
      subroutine bitrv2conj(n, ip, a)
      integer n, ip(0 : *), j, j1, k, k1, l, m, m2
      real*8 a(0 : n - 1), xr, xi, yr, yi
      ip(0) = 0
      l = n
      m = 1
      do while (8 * m .lt. l)
          l = l / 2
          do j = 0, m - 1
              ip(m + j) = ip(j) + l
          end do
          m = m * 2
      end do
      m2 = 2 * m
      if (8 * m .eq. l) then
          do k = 0, m - 1
              do j = 0, k - 1
                  j1 = 2 * j + ip(k)
                  k1 = 2 * k + ip(j)
                  xr = a(j1)
                  xi = -a(j1 + 1)
                  yr = a(k1)
                  yi = -a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr
                  a(k1 + 1) = xi
                  j1 = j1 + m2
                  k1 = k1 + 2 * m2
                  xr = a(j1)
                  xi = -a(j1 + 1)
                  yr = a(k1)
                  yi = -a(k1 + 1)
                  a(j1) = yr
                  a(j1 + 1) = yi
                  a(k1) = xr