/*****************************************************************************

  Licensed to Accellera Systems Initiative Inc. (Accellera) under one or
  more contributor license agreements.  See the NOTICE file distributed
  with this work for additional information regarding copyright ownership.
  Accellera licenses this file to you 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.

 *****************************************************************************/

/*****************************************************************************

  fft.cpp - This is the implementation file for the synchronous process "fft".

  Original Author: Rashmi Goswami, Synopsys, Inc.

 *****************************************************************************/

/*****************************************************************************

  MODIFICATION LOG - modifiers, enter your name, affiliation, date and
  changes you are making here.

      Name, Affiliation, Date:
  Description of Modification:

 *****************************************************************************/


#include "systemc.h"
#include "fft.h"
#include "math.h"

void fft::entry()
{ float sample[16][2];
  unsigned int index;

  while(true)
  { data_req.write(false);
    data_ready.write(false);
    index = 0;
    //Reading in the Samples
      cout << endl << "Reading in the samples..." << endl;
      while( index < 16 )
      {
       data_req.write(true);
       do { wait(); } while (data_valid == true);
       sample[index][0] = in_real.read();
       sample[index][1] = in_imag.read();
       index++;
       data_req.write(false);
       wait();
      }
      index = 0;


      //////////////////////////////////////////////////////////////////////////
      ///  Computation - 1D Complex DFT In-Place DIF Computation Algorithm  ////
      //////////////////////////////////////////////////////////////////////////
    
      //Size of FFT, N = 2**M    
       unsigned int N, M, len ;  
       float theta; 
       float W[7][2], w_real, w_imag, w_rec_real, w_rec_imag, w_temp;

       //Initialize
       M = 4; N = 16; 
       len = N/2;
       theta = 8.0*atan(1.0)/N;

       cout << "Computing..." << endl;

       //Calculate the W-values recursively
        w_real =  cos(theta);
        w_imag =  -sin(theta);

        w_rec_real = 1;
        w_rec_imag = 0;

        index = 0;    
        while(index < len-1) 
        {
           w_temp = w_rec_real*w_real - w_rec_imag*w_imag;
           w_rec_imag =  w_rec_real*w_imag + w_rec_imag*w_real;
           w_rec_real = w_temp;
           W[index][0] = w_rec_real;
           W[index][1] = w_rec_imag;
           index++;
        }


       float tmp_real, tmp_imag, tmp_real2, tmp_imag2;
       unsigned int stage, i, j,index2, windex, incr;
     
      //Begin Computation 
       stage = 0;

       len = N;
       incr = 1;

       while (stage < M)
       { 
        len = len/2;
 
        //First Iteration :  With No Multiplies
          i = 0;
 

          while(i < N)
          {
             index =  i; index2 = index + len; 
             
             tmp_real = sample[index][0] + sample[index2][0];
             tmp_imag = sample[index][1] + sample[index2][1];
 
             sample[index2][0] = sample[index][0] - sample[index2][0];
             sample[index2][1] = sample[index][1] - sample[index2][1];

             sample[index][0] = tmp_real;
             sample[index][1] = tmp_imag;
        

             i = i + 2*len;          
 
          }


        //Remaining Iterations: Use Stored W
         j = 1; windex = incr - 1;
         while (j < len) // This loop executes N/2 times at first stage, .. once at last stage.
         {
            i = j; 
            while (i < N)
            {
              index = i;
              index2 = index + len;

              tmp_real = sample[index][0] + sample[index2][0]; 
              tmp_imag = sample[index][1] + sample[index2][1];
              tmp_real2 = sample[index][0] - sample[index2][0];
              tmp_imag2 = sample[index][1] - sample[index2][1];
  
              sample[index2][0] = tmp_real2*W[windex][0] - tmp_imag2*W[windex][1];
              sample[index2][1] = tmp_real2*W[windex][1] + tmp_imag2*W[windex][0]; 

              sample[index][0] = tmp_real;
              sample[index][1] = tmp_imag;
           
              i = i + 2*len;
              
            }
            windex = windex + incr;
            j++;
         }
          stage++;
          incr = 2*incr;
       } 
           
     //////////////////////////////////////////////////////////////////////////
     
     //Writing out the normalized transform values in bit reversed order
      sc_uint<4> bits_i;
      sc_uint<4> bits_index;
      bits_i = 0;
      i = 0;

      cout << "Writing the transform values..." << endl;
      while( i < 16)
      {
       bits_i = i;
       bits_index[3]= bits_i[0];
       bits_index[2]= bits_i[1];
       bits_index[1]= bits_i[2];
       bits_index[0]= bits_i[3];
       index = bits_index;
       out_real.write(sample[index][0]);
       out_imag.write(sample[index][1]);
       data_ready.write(true);
       do { wait(); } while ( !(data_ack == true) );
       data_ready.write(false);
       i++;
       wait();
      }
      index = 0; 
      cout << "Done..." << endl;
  }
 }
