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diff --git a/src/armadillo/include/armadillo_bits/fft_engine_fftw3.hpp b/src/armadillo/include/armadillo_bits/fft_engine_fftw3.hpp
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@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: Apache-2.0
+// 
+// Copyright 2008-2016 Conrad Sanderson (http://conradsanderson.id.au)
+// Copyright 2008-2016 National ICT Australia (NICTA)
+// 
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// 
+// ------------------------------------------------------------------------
+
+
+//! \addtogroup fft_engine_fftw3
+//! @{
+
+
+#if defined(ARMA_USE_FFTW3)
+
+template<typename cx_type, bool inverse>
+class fft_engine_fftw3
+  {
+  public:
+  
+  constexpr static int fftw3_sign_forward  = -1;
+  constexpr static int fftw3_sign_backward = +1;
+  
+  constexpr static unsigned int fftw3_flag_destroy  = (1u << 0);
+  constexpr static unsigned int fftw3_flag_preserve = (1u << 4);
+  constexpr static unsigned int fftw3_flag_estimate = (1u << 6);
+  
+  const uword N;
+  
+  void_ptr fftw3_plan;
+  
+  podarray<cx_type> X_work;  // for storing copy of input (can be overwritten by FFTW3)
+  podarray<cx_type> Y_work;  // for storing output
+  
+  inline
+  ~fft_engine_fftw3()
+    {
+    arma_extra_debug_sigprint();
+    
+    if(fftw3_plan != nullptr)  { fftw3::destroy_plan<cx_type>(fftw3_plan); }
+    
+    // fftw3::cleanup<cx_type>();  // NOTE: this also removes any wisdom acquired by FFTW3 
+    }
+  
+  inline
+  fft_engine_fftw3(const uword in_N)
+    : N         (in_N   )
+    , fftw3_plan(nullptr)
+    {
+    arma_extra_debug_sigprint();
+    
+    if(N == 0)  { return; }
+    
+    if(N > uword(std::numeric_limits<int>::max()))
+      {
+      arma_stop_runtime_error("integer overflow: FFT size too large for integer type used by FFTW3");
+      }
+    
+    arma_extra_debug_print("fft_engine_fftw3::constructor: allocating work arrays");
+    X_work.set_size(N);
+    Y_work.set_size(N);
+    
+    const int fftw3_sign  = (inverse) ? fftw3_sign_backward : fftw3_sign_forward;
+    const int fftw3_flags = fftw3_flag_destroy | fftw3_flag_estimate;
+    
+    arma_extra_debug_print("fft_engine_fftw3::constructor: generating 1D plan");
+    fftw3_plan = fftw3::plan_dft_1d<cx_type>(N, X_work.memptr(), Y_work.memptr(), fftw3_sign, fftw3_flags);
+    
+    if(fftw3_plan == nullptr)  { arma_stop_runtime_error("fft_engine_fftw3::constructor: failed to create plan"); }
+    }
+  
+  inline
+  void
+  run(cx_type* Y, const cx_type* X)
+    {
+    arma_extra_debug_sigprint();
+    
+    if(fftw3_plan == nullptr)  { return; }
+    
+    arma_extra_debug_print("fft_engine_fftw3::run(): copying input array");
+    arrayops::copy(X_work.memptr(), X, N);
+    
+    arma_extra_debug_print("fft_engine_fftw3::run(): executing plan");
+    fftw3::execute<cx_type>(fftw3_plan);
+    
+    arma_extra_debug_print("fft_engine_fftw3::run(): copying output array");
+    arrayops::copy(Y, Y_work.memptr(), N);
+    }
+  };
+
+#endif
+
+
+//! @}