/*
This file is part of pocketfft.

Copyright (C) 2010-2020 Max-Planck-Society
Copyright (C) 2019 Peter Bell

For the odd-sized DCT-IV transforms:
  Copyright (C) 2003, 2007-14 Matteo Frigo
  Copyright (C) 2003, 2007-14 Massachusetts Institute of Technology

Authors: Martin Reinecke, Peter Bell

All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice, this
  list of conditions and the following disclaimer in the documentation and/or
  other materials provided with the distribution.
* Neither the name of the copyright holder nor the names of its contributors may
  be used to endorse or promote products derived from this software without
  specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#ifndef MRUTIL_FFT_H
#define MRUTIL_FFT_H

#include "mr_util/math/fft1d.h"

#ifndef POCKETFFT_CACHE_SIZE
#define POCKETFFT_CACHE_SIZE 16
#endif

#include <cmath>
#include <cstdlib>
#include <stdexcept>
#include <memory>
#include <vector>
#include <complex>
#include <algorithm>
#if POCKETFFT_CACHE_SIZE!=0
#include <array>
#endif
#include "mr_util/infra/threading.h"
#include "mr_util/infra/simd.h"
#include "mr_util/infra/mav.h"
#ifndef MRUTIL_NO_THREADING
#include <mutex>
#endif

namespace mr {

namespace detail_fft {

constexpr bool FORWARD  = true,
               BACKWARD = false;

struct util // hack to avoid duplicate symbols
  {
  static void sanity_check_axes(size_t ndim, const shape_t &axes)
    {
    shape_t tmp(ndim,0);
    if (axes.empty()) throw std::invalid_argument("no axes specified");
    for (auto ax : axes)
      {
      if (ax>=ndim) throw std::invalid_argument("bad axis number");
      if (++tmp[ax]>1) throw std::invalid_argument("axis specified repeatedly");
      }
    }

  static MRUTIL_NOINLINE void sanity_check_onetype(const fmav_info &a1,
    const fmav_info &a2, bool inplace, const shape_t &axes)
    {
    sanity_check_axes(a1.ndim(), axes);
    MR_assert(a1.conformable(a2), "array sizes are not conformable");
    if (inplace) MR_assert(a1.stride()==a2.stride(), "stride mismatch");
    }
  static MRUTIL_NOINLINE void sanity_check_cr(const fmav_info &ac,
    const fmav_info &ar, const shape_t &axes)
    {
    sanity_check_axes(ac.ndim(), axes);
    MR_assert(ac.ndim()==ar.ndim(), "dimension mismatch");
    for (size_t i=0; i<ac.ndim(); ++i)
      MR_assert(ac.shape(i)== (i==axes.back()) ? (ar.shape(i)/2+1) : ar.shape(i),
        "axis length mismatch");
    }
  static MRUTIL_NOINLINE void sanity_check_cr(const fmav_info &ac,
    const fmav_info &ar, const size_t axis)
    {
    if (axis>=ac.ndim()) throw std::invalid_argument("bad axis number");
    MR_assert(ac.ndim()==ar.ndim(), "dimension mismatch");
    for (size_t i=0; i<ac.ndim(); ++i)
      MR_assert(ac.shape(i)== (i==axis) ? (ar.shape(i)/2+1) : ar.shape(i),
        "axis length mismatch");
    }

#ifdef MRUTIL_NO_THREADING
  static size_t thread_count (size_t /*nthreads*/, const fmav_info &/*info*/,
    size_t /*axis*/, size_t /*vlen*/)
    { return 1; }
#else
  static size_t thread_count (size_t nthreads, const fmav_info &info,
    size_t axis, size_t vlen)
    {
    if (nthreads==1) return 1;
    size_t size = info.size();
    size_t parallel = size / (info.shape(axis) * vlen);
    if (info.shape(axis) < 1000)
      parallel /= 4;
    size_t max_threads = (nthreads==0) ? mr::max_threads() : nthreads;
    return std::max(size_t(1), std::min(parallel, max_threads));
    }
#endif
  };


//
// sine/cosine transforms
//

template<typename T0> class T_dct1
  {
  private:
    pocketfft_r<T0> fftplan;

  public:
    MRUTIL_NOINLINE T_dct1(size_t length)
      : fftplan(2*(length-1)) {}

    template<typename T> MRUTIL_NOINLINE void exec(T c[], T0 fct, bool ortho,
      int /*type*/, bool /*cosine*/) const
      {
      constexpr T0 sqrt2=T0(1.414213562373095048801688724209698L);
      size_t N=fftplan.length(), n=N/2+1;
      if (ortho)
        { c[0]*=sqrt2; c[n-1]*=sqrt2; }
      aligned_array<T> tmp(N);
      tmp[0] = c[0];
      for (size_t i=1; i<n; ++i)
        tmp[i] = tmp[N-i] = c[i];
      fftplan.exec(tmp.data(), fct, true);
      c[0] = tmp[0];
      for (size_t i=1; i<n; ++i)
        c[i] = tmp[2*i-1];
      if (ortho)
        { c[0]*=sqrt2*T0(0.5); c[n-1]*=sqrt2*T0(0.5); }
      }

    size_t length() const { return fftplan.length()/2+1; }
  };

template<typename T0> class T_dst1
  {
  private:
    pocketfft_r<T0> fftplan;

  public:
    MRUTIL_NOINLINE T_dst1(size_t length)
      : fftplan(2*(length+1)) {}

    template<typename T> MRUTIL_NOINLINE void exec(T c[], T0 fct,
      bool /*ortho*/, int /*type*/, bool /*cosine*/) const
      {
      size_t N=fftplan.length(), n=N/2-1;
      aligned_array<T> tmp(N);
      tmp[0] = tmp[n+1] = c[0]*0;
      for (size_t i=0; i<n; ++i)
        { tmp[i+1]=c[i]; tmp[N-1-i]=-c[i]; }
      fftplan.exec(tmp.data(), fct, true);
      for (size_t i=0; i<n; ++i)
        c[i] = -tmp[2*i+2];
      }

    size_t length() const { return fftplan.length()/2-1; }
  };

template<typename T0> class T_dcst23
  {
  private:
    pocketfft_r<T0> fftplan;
    std::vector<T0> twiddle;

  public:
    MRUTIL_NOINLINE T_dcst23(size_t length)
      : fftplan(length), twiddle(length)
      {
      UnityRoots<T0,Cmplx<T0>> tw(4*length);
      for (size_t i=0; i<length; ++i)
        twiddle[i] = tw[i+1].r;
      }

    template<typename T> MRUTIL_NOINLINE void exec(T c[], T0 fct, bool ortho,
      int type, bool cosine) const
      {
      constexpr T0 sqrt2=T0(1.414213562373095048801688724209698L);
      size_t N=length();
      size_t NS2 = (N+1)/2;
      if (type==2)
        {
        if (!cosine)
          for (size_t k=1; k<N; k+=2)
            c[k] = -c[k];
        c[0] *= 2;
        if ((N&1)==0) c[N-1]*=2;
        for (size_t k=1; k<N-1; k+=2)
          MPINPLACE(c[k+1], c[k]);
        fftplan.exec(c, fct, false);
        for (size_t k=1, kc=N-1; k<NS2; ++k, --kc)
          {
          T t1 = twiddle[k-1]*c[kc]+twiddle[kc-1]*c[k];
          T t2 = twiddle[k-1]*c[k]-twiddle[kc-1]*c[kc];
          c[k] = T0(0.5)*(t1+t2); c[kc]=T0(0.5)*(t1-t2);
          }
        if ((N&1)==0)
          c[NS2] *= twiddle[NS2-1];
        if (!cosine)
          for (size_t k=0, kc=N-1; k<kc; ++k, --kc)
            std::swap(c[k], c[kc]);
        if (ortho) c[0]*=sqrt2*T0(0.5);
        }
      else
        {
        if (ortho) c[0]*=sqrt2;
        if (!cosine)
          for (size_t k=0, kc=N-1; k<NS2; ++k, --kc)
            std::swap(c[k], c[kc]);
        for (size_t k=1, kc=N-1; k<NS2; ++k, --kc)
          {
          T t1=c[k]+c[kc], t2=c[k]-c[kc];
          c[k] = twiddle[k-1]*t2+twiddle[kc-1]*t1;
          c[kc]= twiddle[k-1]*t1-twiddle[kc-1]*t2;
          }
        if ((N&1)==0)
          c[NS2] *= 2*twiddle[NS2-1];
        fftplan.exec(c, fct, true);
        for (size_t k=1; k<N-1; k+=2)
          MPINPLACE(c[k], c[k+1]);
        if (!cosine)
          for (size_t k=1; k<N; k+=2)
            c[k] = -c[k];
        }
      }

    size_t length() const { return fftplan.length(); }
  };

template<typename T0> class T_dcst4
  {
  private:
    size_t N;
    std::unique_ptr<pocketfft_c<T0>> fft;
    std::unique_ptr<pocketfft_r<T0>> rfft;
    aligned_array<Cmplx<T0>> C2;

  public:
    MRUTIL_NOINLINE T_dcst4(size_t length)
      : N(length),
        fft((N&1) ? nullptr : new pocketfft_c<T0>(N/2)),
        rfft((N&1)? new pocketfft_r<T0>(N) : nullptr),
        C2((N&1) ? 0 : N/2)
      {
      if ((N&1)==0)
        {
        UnityRoots<T0,Cmplx<T0>> tw(16*N);
        for (size_t i=0; i<N/2; ++i)
          C2[i] = conj(tw[8*i+1]);
        }
      }

    template<typename T> MRUTIL_NOINLINE void exec(T c[], T0 fct,
      bool /*ortho*/, int /*type*/, bool cosine) const
      {
      size_t n2 = N/2;
      if (!cosine)
        for (size_t k=0, kc=N-1; k<n2; ++k, --kc)
          std::swap(c[k], c[kc]);
      if (N&1)
        {
        // The following code is derived from the FFTW3 function apply_re11()
        // and is released under the 3-clause BSD license with friendly
        // permission of Matteo Frigo and Steven G. Johnson.

        aligned_array<T> y(N);
        {
        size_t i=0, m=n2;
        for (; m<N; ++i, m+=4)
          y[i] = c[m];
        for (; m<2*N; ++i, m+=4)
          y[i] = -c[2*N-m-1];
        for (; m<3*N; ++i, m+=4)
          y[i] = -c[m-2*N];
        for (; m<4*N; ++i, m+=4)
          y[i] = c[4*N-m-1];
        for (; i<N; ++i, m+=4)
          y[i] = c[m-4*N];
        }
        rfft->exec(y.data(), fct, true);
        {
        auto SGN = [](size_t i)
           {
           constexpr T0 sqrt2=T0(1.414213562373095048801688724209698L);
           return (i&2) ? -sqrt2 : sqrt2;
           };
        c[n2] = y[0]*SGN(n2+1);
        size_t i=0, i1=1, k=1;
        for (; k<n2; ++i, ++i1, k+=2)
          {
          c[i    ] = y[2*k-1]*SGN(i1)     + y[2*k  ]*SGN(i);
          c[N -i1] = y[2*k-1]*SGN(N -i)   - y[2*k  ]*SGN(N -i1);
          c[n2-i1] = y[2*k+1]*SGN(n2-i)   - y[2*k+2]*SGN(n2-i1);
          c[n2+i1] = y[2*k+1]*SGN(n2+i+2) + y[2*k+2]*SGN(n2+i1);
          }
        if (k == n2)
          {
          c[i   ] = y[2*k-1]*SGN(i+1) + y[2*k]*SGN(i);
          c[N-i1] = y[2*k-1]*SGN(i+2) + y[2*k]*SGN(i1);
          }
        }

        // FFTW-derived code ends here
        }
      else
        {
        // even length algorithm from
        // https://www.appletonaudio.com/blog/2013/derivation-of-fast-dct-4-algorithm-based-on-dft/
        aligned_array<Cmplx<T>> y(n2);
        for(size_t i=0; i<n2; ++i)
          {
          y[i].Set(c[2*i],c[N-1-2*i]);
          y[i] *= C2[i];
          }
        fft->exec(y.data(), fct, true);
        for(size_t i=0, ic=n2-1; i<n2; ++i, --ic)
          {
          c[2*i  ] = T0( 2)*(y[i ].r*C2[i ].r-y[i ].i*C2[i ].i);
          c[2*i+1] = T0(-2)*(y[ic].i*C2[ic].r+y[ic].r*C2[ic].i);
          }
        }
      if (!cosine)
        for (size_t k=1; k<N; k+=2)
          c[k] = -c[k];
      }

    size_t length() const { return N; }
  };


//
// multi-D infrastructure
//

template<typename T> std::shared_ptr<T> get_plan(size_t length)
  {
#if POCKETFFT_CACHE_SIZE==0
  return std::make_shared<T>(length);
#else
  constexpr size_t nmax=POCKETFFT_CACHE_SIZE;
  static std::array<std::shared_ptr<T>, nmax> cache;
  static std::array<size_t, nmax> last_access{{0}};
  static size_t access_counter = 0;

  auto find_in_cache = [&]() -> std::shared_ptr<T>
    {
    for (size_t i=0; i<nmax; ++i)
      if (cache[i] && (cache[i]->length()==length))
        {
        // no need to update if this is already the most recent entry
        if (last_access[i]!=access_counter)
          {
          last_access[i] = ++access_counter;
          // Guard against overflow
          if (access_counter == 0)
            last_access.fill(0);
          }
        return cache[i];
        }

    return nullptr;
    };
#ifdef MRUTIL_NO_THREADING
  auto p = find_in_cache();
  if (p) return p;
  auto plan = std::make_shared<T>(length);
  size_t lru = 0;
  for (size_t i=1; i<nmax; ++i)
    if (last_access[i] < last_access[lru])
      lru = i;

  cache[lru] = plan;
  last_access[lru] = ++access_counter;
  return plan;
#else
  static std::mutex mut;

  {
  std::lock_guard<std::mutex> lock(mut);
  auto p = find_in_cache();
  if (p) return p;
  }
  auto plan = std::make_shared<T>(length);
  {
  std::lock_guard<std::mutex> lock(mut);
  auto p = find_in_cache();
  if (p) return p;

  size_t lru = 0;
  for (size_t i=1; i<nmax; ++i)
    if (last_access[i] < last_access[lru])
      lru = i;

  cache[lru] = plan;
  last_access[lru] = ++access_counter;
  }
  return plan;
#endif
#endif
  }

template<size_t N> class multi_iter
  {
  private:
    shape_t pos;
    fmav_info iarr, oarr;
    ptrdiff_t p_ii, p_i[N], str_i, p_oi, p_o[N], str_o;
    size_t idim, rem;

    void advance_i()
      {
      for (int i_=int(pos.size())-1; i_>=0; --i_)
        {
        auto i = size_t(i_);
        if (i==idim) continue;
        p_ii += iarr.stride(i);
        p_oi += oarr.stride(i);
        if (++pos[i] < iarr.shape(i))
          return;
        pos[i] = 0;
        p_ii -= ptrdiff_t(iarr.shape(i))*iarr.stride(i);
        p_oi -= ptrdiff_t(oarr.shape(i))*oarr.stride(i);
        }
      }

  public:
    multi_iter(const fmav_info &iarr_, const fmav_info &oarr_, size_t idim_,
        size_t nshares, size_t myshare)
      : pos(iarr_.ndim(), 0), iarr(iarr_), oarr(oarr_), p_ii(0),
        str_i(iarr.stride(idim_)), p_oi(0), str_o(oarr.stride(idim_)),
        idim(idim_), rem(iarr.size()/iarr.shape(idim))
      {
      if (nshares==1) return;
      if (nshares==0) throw std::runtime_error("can't run with zero threads");
      if (myshare>=nshares) throw std::runtime_error("impossible share requested");
      size_t nbase = rem/nshares;
      size_t additional = rem%nshares;
      size_t lo = myshare*nbase + ((myshare<additional) ? myshare : additional);
      size_t hi = lo+nbase+(myshare<additional);
      size_t todo = hi-lo;

      size_t chunk = rem;
      for (size_t i=0; i<pos.size(); ++i)
        {
        if (i==idim) continue;
        chunk /= iarr.shape(i);
        size_t n_advance = lo/chunk;
        pos[i] += n_advance;
        p_ii += ptrdiff_t(n_advance)*iarr.stride(i);
        p_oi += ptrdiff_t(n_advance)*oarr.stride(i);
        lo -= n_advance*chunk;
        }
      rem = todo;
      }
    void advance(size_t n)
      {
      if (rem<n) throw std::runtime_error("underrun");
      for (size_t i=0; i<n; ++i)
        {
        p_i[i] = p_ii;
        p_o[i] = p_oi;
        advance_i();
        }
      rem -= n;
      }
    ptrdiff_t iofs(size_t i) const { return p_i[0] + ptrdiff_t(i)*str_i; }
    ptrdiff_t iofs(size_t j, size_t i) const { return p_i[j] + ptrdiff_t(i)*str_i; }
    ptrdiff_t oofs(size_t i) const { return p_o[0] + ptrdiff_t(i)*str_o; }
    ptrdiff_t oofs(size_t j, size_t i) const { return p_o[j] + ptrdiff_t(i)*str_o; }
    size_t length_in() const { return iarr.shape(idim); }
    size_t length_out() const { return oarr.shape(idim); }
    ptrdiff_t stride_in() const { return str_i; }
    ptrdiff_t stride_out() const { return str_o; }
    size_t remaining() const { return rem; }
  };

class simple_iter
  {
  private:
    shape_t pos;
    fmav_info arr;
    ptrdiff_t p;
    size_t rem;

  public:
    simple_iter(const fmav_info &arr_)
      : pos(arr_.ndim(), 0), arr(arr_), p(0), rem(arr_.size()) {}
    void advance()
      {
      --rem;
      for (int i_=int(pos.size())-1; i_>=0; --i_)
        {
        auto i = size_t(i_);
        p += arr.stride(i);
        if (++pos[i] < arr.shape(i))
          return;
        pos[i] = 0;
        p -= ptrdiff_t(arr.shape(i))*arr.stride(i);
        }
      }
    ptrdiff_t ofs() const { return p; }
    size_t remaining() const { return rem; }
  };

class rev_iter
  {
  private:
    shape_t pos;
    fmav_info arr;
    std::vector<char> rev_axis;
    std::vector<char> rev_jump;
    size_t last_axis, last_size;
    shape_t shp;
    ptrdiff_t p, rp;
    size_t rem;

  public:
    rev_iter(const fmav_info &arr_, const shape_t &axes)
      : pos(arr_.ndim(), 0), arr(arr_), rev_axis(arr_.ndim(), 0),
        rev_jump(arr_.ndim(), 1), p(0), rp(0)
      {
      for (auto ax: axes)
        rev_axis[ax]=1;
      last_axis = axes.back();
      last_size = arr.shape(last_axis)/2 + 1;
      shp = arr.shape();
      shp[last_axis] = last_size;
      rem=1;
      for (auto i: shp)
        rem *= i;
      }
    void advance()
      {
      --rem;
      for (int i_=int(pos.size())-1; i_>=0; --i_)
        {
        auto i = size_t(i_);
        p += arr.stride(i);
        if (!rev_axis[i])
          rp += arr.stride(i);
        else
          {
          rp -= arr.stride(i);
          if (rev_jump[i])
            {
            rp += ptrdiff_t(arr.shape(i))*arr.stride(i);
            rev_jump[i] = 0;
            }
          }
        if (++pos[i] < shp[i])
          return;
        pos[i] = 0;
        p -= ptrdiff_t(shp[i])*arr.stride(i);
        if (rev_axis[i])
          {
          rp -= ptrdiff_t(arr.shape(i)-shp[i])*arr.stride(i);
          rev_jump[i] = 1;
          }
        else
          rp -= ptrdiff_t(shp[i])*arr.stride(i);
        }
      }
    ptrdiff_t ofs() const { return p; }
    ptrdiff_t rev_ofs() const { return rp; }
    size_t remaining() const { return rem; }
  };

template<typename T, typename T0> aligned_array<T> alloc_tmp
  (const fmav_info &info, size_t axsize)
  {
  auto othersize = info.size()/axsize;
  constexpr auto vlen = native_simd<T0>::size();
  auto tmpsize = axsize*((othersize>=vlen) ? vlen : 1);
  return aligned_array<T>(tmpsize);
  }

template <typename T, size_t vlen> void copy_input(const multi_iter<vlen> &it,
  const fmav<Cmplx<T>> &src, Cmplx<native_simd<T>> *MRUTIL_RESTRICT dst)
  {
  for (size_t i=0; i<it.length_in(); ++i)
    for (size_t j=0; j<vlen; ++j)
      {
      dst[i].r[j] = src[it.iofs(j,i)].r;
      dst[i].i[j] = src[it.iofs(j,i)].i;
      }
  }

template <typename T, size_t vlen> void copy_input(const multi_iter<vlen> &it,
  const fmav<T> &src, native_simd<T> *MRUTIL_RESTRICT dst)
  {
  for (size_t i=0; i<it.length_in(); ++i)
    for (size_t j=0; j<vlen; ++j)
      dst[i][j] = src[it.iofs(j,i)];
  }

template <typename T, size_t vlen> void copy_input(const multi_iter<vlen> &it,
  const fmav<T> &src, T *MRUTIL_RESTRICT dst)
  {
  if (dst == &src[it.iofs(0)]) return;  // in-place
  for (size_t i=0; i<it.length_in(); ++i)
    dst[i] = src[it.iofs(i)];
  }

template<typename T, size_t vlen> void copy_output(const multi_iter<vlen> &it,
  const Cmplx<native_simd<T>> *MRUTIL_RESTRICT src, fmav<Cmplx<T>> &dst)
  {
  auto ptr=dst.vdata();
  for (size_t i=0; i<it.length_out(); ++i)
    for (size_t j=0; j<vlen; ++j)
      ptr[it.oofs(j,i)].Set(src[i].r[j],src[i].i[j]);
  }

template<typename T, size_t vlen> void copy_output(const multi_iter<vlen> &it,
  const native_simd<T> *MRUTIL_RESTRICT src, fmav<T> &dst)
  {
  auto ptr=dst.vdata();
  for (size_t i=0; i<it.length_out(); ++i)
    for (size_t j=0; j<vlen; ++j)
      ptr[it.oofs(j,i)] = src[i][j];
  }

template<typename T, size_t vlen> void copy_output(const multi_iter<vlen> &it,
  const T *MRUTIL_RESTRICT src, fmav<T> &dst)
  {
  auto ptr=dst.vdata();
  if (src == &dst[it.oofs(0)]) return;  // in-place
  for (size_t i=0; i<it.length_out(); ++i)
    ptr[it.oofs(i)] = src[i];
  }

template <typename T> struct add_vec { using type = native_simd<T>; };
template <typename T> struct add_vec<Cmplx<T>>
  { using type = Cmplx<native_simd<T>>; };
template <typename T> using add_vec_t = typename add_vec<T>::type;

template<typename Tplan, typename T, typename T0, typename Exec>
MRUTIL_NOINLINE void general_nd(const fmav<T> &in, fmav<T> &out,
  const shape_t &axes, T0 fct, size_t nthreads, const Exec & exec,
  const bool allow_inplace=true)
  {
  std::shared_ptr<Tplan> plan;

  for (size_t iax=0; iax<axes.size(); ++iax)
    {
    size_t len=in.shape(axes[iax]);
    if ((!plan) || (len!=plan->length()))
      plan = get_plan<Tplan>(len);

    execParallel(
      util::thread_count(nthreads, in, axes[iax], native_simd<T0>::size()),
      [&](Scheduler &sched) {
        constexpr auto vlen = native_simd<T0>::size();
        auto storage = alloc_tmp<T,T0>(in, len);
        const auto &tin(iax==0? in : out);
        multi_iter<vlen> it(tin, out, axes[iax], sched.num_threads(), sched.thread_num());
#ifndef MRUTIL_NO_SIMD
        if (vlen>1)
          while (it.remaining()>=vlen)
            {
            it.advance(vlen);
            auto tdatav = reinterpret_cast<add_vec_t<T> *>(storage.data());
            exec(it, tin, out, tdatav, *plan, fct);
            }
#endif
        while (it.remaining()>0)
          {
          it.advance(1);
          auto buf = allow_inplace && it.stride_out() == 1 ?
            &out.vraw(it.oofs(0)) : reinterpret_cast<T *>(storage.data());
          exec(it, tin, out, buf, *plan, fct);
          }
      });  // end of parallel region
    fct = T0(1); // factor has been applied, use 1 for remaining axes
    }
  }

struct ExecC2C
  {
  bool forward;

  template <typename T0, typename T, size_t vlen> void operator() (
    const multi_iter<vlen> &it, const fmav<Cmplx<T0>> &in,
    fmav<Cmplx<T0>> &out, T *buf, const pocketfft_c<T0> &plan, T0 fct) const
    {
    copy_input(it, in, buf);
    plan.exec(buf, fct, forward);
    copy_output(it, buf, out);
    }
  };

template <typename T, size_t vlen> void copy_hartley(const multi_iter<vlen> &it,
  const native_simd<T> *MRUTIL_RESTRICT src, fmav<T> &dst)
  {
  auto ptr = dst.vdata();
  for (size_t j=0; j<vlen; ++j)
    ptr[it.oofs(j,0)] = src[0][j];
  size_t i=1, i1=1, i2=it.length_out()-1;
  for (i=1; i<it.length_out()-1; i+=2, ++i1, --i2)
    for (size_t j=0; j<vlen; ++j)
      {
      ptr[it.oofs(j,i1)] = src[i][j]+src[i+1][j];
      ptr[it.oofs(j,i2)] = src[i][j]-src[i+1][j];
      }
  if (i<it.length_out())
    for (size_t j=0; j<vlen; ++j)
      ptr[it.oofs(j,i1)] = src[i][j];
  }

template <typename T, size_t vlen> void copy_hartley(const multi_iter<vlen> &it,
  const T *MRUTIL_RESTRICT src, fmav<T> &dst)
  {
  auto ptr = dst.vdata();
  ptr[it.oofs(0)] = src[0];
  size_t i=1, i1=1, i2=it.length_out()-1;
  for (i=1; i<it.length_out()-1; i+=2, ++i1, --i2)
    {
    ptr[it.oofs(i1)] = src[i]+src[i+1];
    ptr[it.oofs(i2)] = src[i]-src[i+1];
    }
  if (i<it.length_out())
    ptr[it.oofs(i1)] = src[i];
  }

struct ExecHartley
  {
  template <typename T0, typename T, size_t vlen> void operator () (
    const multi_iter<vlen> &it, const fmav<T0> &in, fmav<T0> &out,
    T * buf, const pocketfft_r<T0> &plan, T0 fct) const
    {
    copy_input(it, in, buf);
    plan.exec(buf, fct, true);
    copy_hartley(it, buf, out);
    }
  };

struct ExecDcst
  {
  bool ortho;
  int type;
  bool cosine;

  template <typename T0, typename T, typename Tplan, size_t vlen>
  void operator () (const multi_iter<vlen> &it, const fmav<T0> &in,
    fmav <T0> &out, T * buf, const Tplan &plan, T0 fct) const
    {
    copy_input(it, in, buf);
    plan.exec(buf, fct, ortho, type, cosine);
    copy_output(it, buf, out);
    }
  };

template<typename T> MRUTIL_NOINLINE void general_r2c(
  const fmav<T> &in, fmav<Cmplx<T>> &out, size_t axis, bool forward, T fct,
  size_t nthreads)
  {
  auto plan = get_plan<pocketfft_r<T>>(in.shape(axis));
  size_t len=in.shape(axis);
  execParallel(
    util::thread_count(nthreads, in, axis, native_simd<T>::size()),
    [&](Scheduler &sched) {
    constexpr auto vlen = native_simd<T>::size();
    auto storage = alloc_tmp<T,T>(in, len);
    multi_iter<vlen> it(in, out, axis, sched.num_threads(), sched.thread_num());
#ifndef MRUTIL_NO_SIMD
    if (vlen>1)
      while (it.remaining()>=vlen)
        {
        it.advance(vlen);
        auto tdatav = reinterpret_cast<native_simd<T> *>(storage.data());
        copy_input(it, in, tdatav);
        plan->exec(tdatav, fct, true);
        auto vout = out.vdata();
        for (size_t j=0; j<vlen; ++j)
          vout[it.oofs(j,0)].Set(tdatav[0][j]);
        size_t i=1, ii=1;
        if (forward)
          for (; i<len-1; i+=2, ++ii)
            for (size_t j=0; j<vlen; ++j)
              vout[it.oofs(j,ii)].Set(tdatav[i][j], tdatav[i+1][j]);
        else
          for (; i<len-1; i+=2, ++ii)
            for (size_t j=0; j<vlen; ++j)
              vout[it.oofs(j,ii)].Set(tdatav[i][j], -tdatav[i+1][j]);
        if (i<len)
          for (size_t j=0; j<vlen; ++j)
            vout[it.oofs(j,ii)].Set(tdatav[i][j]);
        }
#endif
    while (it.remaining()>0)
      {
      it.advance(1);
      auto tdata = reinterpret_cast<T *>(storage.data());
      copy_input(it, in, tdata);
      plan->exec(tdata, fct, true);
      auto vout = out.vdata();
      vout[it.oofs(0)].Set(tdata[0]);
      size_t i=1, ii=1;
      if (forward)
        for (; i<len-1; i+=2, ++ii)
          vout[it.oofs(ii)].Set(tdata[i], tdata[i+1]);
      else
        for (; i<len-1; i+=2, ++ii)
          vout[it.oofs(ii)].Set(tdata[i], -tdata[i+1]);
      if (i<len)
        vout[it.oofs(ii)].Set(tdata[i]);
      }
    });  // end of parallel region
  }
template<typename T> MRUTIL_NOINLINE void general_c2r(
  const fmav<Cmplx<T>> &in, fmav<T> &out, size_t axis, bool forward, T fct,
  size_t nthreads)
  {
  auto plan = get_plan<pocketfft_r<T>>(out.shape(axis));
  size_t len=out.shape(axis);
  execParallel(
    util::thread_count(nthreads, in, axis, native_simd<T>::size()),
    [&](Scheduler &sched) {
      constexpr auto vlen = native_simd<T>::size();
      auto storage = alloc_tmp<T,T>(out, len);
      multi_iter<vlen> it(in, out, axis, sched.num_threads(), sched.thread_num());
#ifndef MRUTIL_NO_SIMD
      if (vlen>1)
        while (it.remaining()>=vlen)
          {
          it.advance(vlen);
          auto tdatav = reinterpret_cast<native_simd<T> *>(storage.data());
          for (size_t j=0; j<vlen; ++j)
            tdatav[0][j]=in[it.iofs(j,0)].r;
          {
          size_t i=1, ii=1;
          if (forward)
            for (; i<len-1; i+=2, ++ii)
              for (size_t j=0; j<vlen; ++j)
                {
                tdatav[i  ][j] =  in[it.iofs(j,ii)].r;
                tdatav[i+1][j] = -in[it.iofs(j,ii)].i;
                }
          else
            for (; i<len-1; i+=2, ++ii)
              for (size_t j=0; j<vlen; ++j)
                {
                tdatav[i  ][j] = in[it.iofs(j,ii)].r;
                tdatav[i+1][j] = in[it.iofs(j,ii)].i;
                }
          if (i<len)
            for (size_t j=0; j<vlen; ++j)
              tdatav[i][j] = in[it.iofs(j,ii)].r;
          }
          plan->exec(tdatav, fct, false);
          copy_output(it, tdatav, out);
          }
#endif
      while (it.remaining()>0)
        {
        it.advance(1);
        auto tdata = reinterpret_cast<T *>(storage.data());
        tdata[0]=in[it.iofs(0)].r;
        {
        size_t i=1, ii=1;
        if (forward)
          for (; i<len-1; i+=2, ++ii)
            {
            tdata[i  ] =  in[it.iofs(ii)].r;
            tdata[i+1] = -in[it.iofs(ii)].i;
            }
        else
          for (; i<len-1; i+=2, ++ii)
            {
            tdata[i  ] = in[it.iofs(ii)].r;
            tdata[i+1] = in[it.iofs(ii)].i;
            }
        if (i<len)
          tdata[i] = in[it.iofs(ii)].r;
        }
        plan->exec(tdata, fct, false);
        copy_output(it, tdata, out);
        }
    });  // end of parallel region
  }

struct ExecR2R
  {
  bool r2c, forward;

  template <typename T0, typename T, size_t vlen> void operator () (
    const multi_iter<vlen> &it, const fmav<T0> &in, fmav<T0> &out, T * buf,
    const pocketfft_r<T0> &plan, T0 fct) const
    {
    copy_input(it, in, buf);
    if ((!r2c) && forward)
      for (size_t i=2; i<it.length_out(); i+=2)
        buf[i] = -buf[i];
    plan.exec(buf, fct, forward);
    if (r2c && (!forward))
      for (size_t i=2; i<it.length_out(); i+=2)
        buf[i] = -buf[i];
    copy_output(it, buf, out);
    }
  };

template<typename T> void c2c(const fmav<std::complex<T>> &in,
  fmav<std::complex<T>> &out, const shape_t &axes, bool forward,
  T fct, size_t nthreads=1)
  {
  util::sanity_check_onetype(in, out, in.data()==out.data(), axes);
  if (in.size()==0) return;
  fmav<Cmplx<T>> in2(reinterpret_cast<const Cmplx<T> *>(in.data()), in);
  fmav<Cmplx<T>> out2(reinterpret_cast<Cmplx<T> *>(out.vdata()), out, out.writable());
  general_nd<pocketfft_c<T>>(in2, out2, axes, fct, nthreads, ExecC2C{forward});
  }

template<typename T> void dct(const fmav<T> &in, fmav<T> &out,
  const shape_t &axes, int type, T fct, bool ortho, size_t nthreads=1)
  {
  if ((type<1) || (type>4)) throw std::invalid_argument("invalid DCT type");
  util::sanity_check_onetype(in, out, in.data()==out.data(), axes);
  if (in.size()==0) return;
  const ExecDcst exec{ortho, type, true};
  if (type==1)
    general_nd<T_dct1<T>>(in, out, axes, fct, nthreads, exec);
  else if (type==4)
    general_nd<T_dcst4<T>>(in, out, axes, fct, nthreads, exec);
  else
    general_nd<T_dcst23<T>>(in, out, axes, fct, nthreads, exec);
  }

template<typename T> void dst(const fmav<T> &in, fmav<T> &out,
  const shape_t &axes, int type, T fct, bool ortho, size_t nthreads=1)
  {
  if ((type<1) || (type>4)) throw std::invalid_argument("invalid DST type");
  util::sanity_check_onetype(in, out, in.data()==out.data(), axes);
  const ExecDcst exec{ortho, type, false};
  if (type==1)
    general_nd<T_dst1<T>>(in, out, axes, fct, nthreads, exec);
  else if (type==4)
    general_nd<T_dcst4<T>>(in, out, axes, fct, nthreads, exec);
  else
    general_nd<T_dcst23<T>>(in, out, axes, fct, nthreads, exec);
  }

template<typename T> void r2c(const fmav<T> &in,
  fmav<std::complex<T>> &out, size_t axis, bool forward, T fct,
  size_t nthreads=1)
  {
  util::sanity_check_cr(out, in, axis);
  if (in.size()==0) return;
  fmav<Cmplx<T>> out2(reinterpret_cast<Cmplx<T> *>(out.vdata()), out, out.writable());
  general_r2c(in, out2, axis, forward, fct, nthreads);
  }

template<typename T> void r2c(const fmav<T> &in,
  fmav<std::complex<T>> &out, const shape_t &axes,
  bool forward, T fct, size_t nthreads=1)
  {
  util::sanity_check_cr(out, in, axes);
  if (in.size()==0) return;
  r2c(in, out, axes.back(), forward, fct, nthreads);
  if (axes.size()==1) return;

  auto newaxes = shape_t{axes.begin(), --axes.end()};
  c2c(out, out, newaxes, forward, T(1), nthreads);
  }

template<typename T> void c2r(const fmav<std::complex<T>> &in,
  fmav<T> &out,  size_t axis, bool forward, T fct, size_t nthreads=1)
  {
  util::sanity_check_cr(in, out, axis);
  if (in.size()==0) return;
  fmav<Cmplx<T>> in2(reinterpret_cast<const Cmplx<T> *>(in.data()), in);
  general_c2r(in2, out, axis, forward, fct, nthreads);
  }

template<typename T> void c2r(const fmav<std::complex<T>> &in,
  fmav<T> &out, const shape_t &axes, bool forward, T fct,
  size_t nthreads=1)
  {
  if (axes.size()==1)
    return c2r(in, out, axes[0], forward, fct, nthreads);
  util::sanity_check_cr(in, out, axes);
  if (in.size()==0) return;
  fmav<std::complex<T>> atmp(in.shape());
  auto newaxes = shape_t{axes.begin(), --axes.end()};
  c2c(in, atmp, newaxes, forward, T(1), nthreads);
  c2r(atmp, out, axes.back(), forward, fct, nthreads);
  }

template<typename T> void r2r_fftpack(const fmav<T> &in,
  fmav<T> &out, const shape_t &axes, bool real2hermitian, bool forward,
  T fct, size_t nthreads=1)
  {
  util::sanity_check_onetype(in, out, in.data()==out.data(), axes);
  if (in.size()==0) return;
  general_nd<pocketfft_r<T>>(in, out, axes, fct, nthreads,
    ExecR2R{real2hermitian, forward});
  }

template<typename T> void r2r_separable_hartley(const fmav<T> &in,
  fmav<T> &out, const shape_t &axes, T fct, size_t nthreads=1)
  {
  util::sanity_check_onetype(in, out, in.data()==out.data(), axes);
  if (in.size()==0) return;
  general_nd<pocketfft_r<T>>(in, out, axes, fct, nthreads, ExecHartley{},
    false);
  }

template<typename T> void r2r_genuine_hartley(const fmav<T> &in,
  fmav<T> &out, const shape_t &axes, T fct, size_t nthreads=1)
  {
  if (axes.size()==1)
    return r2r_separable_hartley(in, out, axes, fct, nthreads);
  util::sanity_check_onetype(in, out, in.data()==out.data(), axes);
  if (in.size()==0) return;
  shape_t tshp(in.shape());
  tshp[axes.back()] = tshp[axes.back()]/2+1;
  fmav<std::complex<T>> atmp(tshp);
  r2c(in, atmp, axes, true, fct, nthreads);
  simple_iter iin(atmp);
  rev_iter iout(out, axes);
  auto vout = out.vdata();
  while(iin.remaining()>0)
    {
    auto v = atmp[iin.ofs()];
    vout[iout.ofs()] = v.real()+v.imag();
    vout[iout.rev_ofs()] = v.real()-v.imag();
    iin.advance(); iout.advance();
    }
  }

} // namespace detail_fft

using detail_fft::FORWARD;
using detail_fft::BACKWARD;
using detail_fft::c2c;
using detail_fft::c2r;
using detail_fft::r2c;
using detail_fft::r2r_fftpack;
using detail_fft::r2r_separable_hartley;
using detail_fft::r2r_genuine_hartley;
using detail_fft::dct;
using detail_fft::dst;

} // namespace mr

#endif // POCKETFFT_HDRONLY_H