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

  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:

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


/* This is the implementation file for the synchronous process "fft" */
#include "systemc.h"
#include "fft.h"


//Function for butterfly computation

 void func_butterfly
    ( const sc_int<16>& w_real   /* snps width 16 */,
      const sc_int<16>& w_imag   /* snps width 16 */, 
      const sc_int<16>& real1_in /* snps width 16 */,
      const sc_int<16>& imag1_in /* snps width 16 */,
      const sc_int<16>& real2_in /* snps width 16 */,
      const sc_int<16>& imag2_in /* snps width 16 */,
      sc_int<16>& real1_out /* snps width 16 */,
      sc_int<16>& imag1_out /* snps width 16 */,
      sc_int<16>& real2_out /* snps width 16 */,
      sc_int<16>& imag2_out /* snps width 16 */
    )
 {

   // Variable declarations
     sc_int<17> tmp_real1;
     sc_int<17> tmp_imag1;
     sc_int<17> tmp_real2;
     sc_int<17> tmp_imag2;
     sc_int<34> tmp_real3;
     sc_int<34> tmp_imag3;
  

    // Begin Computation

    tmp_real1 = real1_in + real2_in; 

    // <s,6,10> = <s,5,10> + <s,5,10>
    tmp_imag1 = imag1_in + imag2_in;

    // <s,6,10> = <s,5,10> - <s,5,10>
    tmp_real2 = real1_in - real2_in;

    // <s,6,10> = <s,5,10> - <s,5,10>
    tmp_imag2 = imag1_in - imag2_in;

    //   <s,13,20> = <s,6,10>*<s,5,10> - <s,6,10>*<s,5,10>
    tmp_real3 = tmp_real2*w_real - tmp_imag2*w_imag;

    //   <s,13,20> = <s,6,10>*<s,5,10> - <s,6,10>*<s,5,10>
    tmp_imag3 = tmp_real2*w_imag + tmp_imag2*w_real; 

    // assign the sign-bit(MSB)      
    real1_out[15] = tmp_real1[16];
    imag1_out[15] = tmp_imag1[16];

    // assign the rest of the bits
    real1_out.range(14,0) = tmp_real1.range(14,0);
    imag1_out.range(14,0) = tmp_imag1.range(14,0);

   // assign the sign-bit(MSB)      
    real2_out[15] = tmp_real3[33];
    imag2_out[15] = tmp_imag3[33];          

   // assign the rest of the bits
    real2_out.range(14,0) = tmp_real3.range(24,10);
    imag2_out.range(14,0) = tmp_imag3.range(24,10);

 } // end func_butterfly

void fft::entry()
{ 
 // Variable Declarations
  sc_int<16> real[16];
  sc_int<16> imag[16];
  sc_int<16> tmp_real;
  sc_int<16> tmp_imag;
  short index;
  sc_int<6> N;  
  sc_int<4> M;
  sc_int<6> len;
  sc_int<16> W_real[7];
  sc_int<16> W_imag[7];
  sc_int<16> w_real;
  sc_int<16> w_imag;
  sc_int<16> w_rec_real;
  sc_int<16> w_rec_imag;
  sc_int<32> w_temp1;
  sc_int<32> w_temp2;
  sc_int<32> w_temp3;
  sc_int<32> w_temp4;
  sc_int<33> w_temp5;
  sc_int<33> w_temp6;
  sc_int<16> real1_in;
  sc_int<16> imag1_in;
  sc_int<16> real2_in;
  sc_int<16> imag2_in;
  sc_int<16> real1_out;
  sc_int<16> imag1_out;
  sc_int<16> real2_out;
  sc_int<16> imag2_out;
  sc_int<4> stage;
  short i;
  short j;
  short index2;
  short windex;
  short incr;

  while(true)
  { data_req.write(false);
    data_ready.write(false);
    index = 0; 
     
    wait();
    //Read in the Sample values
      cout << endl << "Reading in the samples..." << endl;
      while( index < 16 )
      {
       data_req.write(true);
       do { wait(); } while ( !(data_valid == true) );
       tmp_real = in_real.read();
       tmp_imag = in_imag.read();
       real[index] = tmp_real;
       imag[index] = tmp_imag;
       index++;
       data_req.write(false);
       wait();
      }
      index = 0;

 
       // Initialize
       M = 4; N = 16; 
       len = N >> 1;

       cout << "Computing..." << endl;
       // Calculate the W-values recursively
       // <'s'/'u',m,n>: is used in comments to denote a fixed point representation
       // 's'- signed, 'u'- unsigned, m - no. of integer bits, n - no. of fractional bits

       //  theta = 8.0*atan(1.0)/N; theta = 22.5 degree

       //  w_real =  cos(theta) = 0.92 (000000.1110101110) <s,5,10>
           w_real =  942;

       //  w_imag = -sin(theta) = -0.38(111111.1001111010) <s,5,10>
           w_imag = -389;

       //  w_rec_real = 1(0000001.0000000000)
	   w_rec_real = 1024;

       //  w_rec_real = 0(000000.0000000000)	 
           w_rec_imag = 0;

        unsigned short w_index;

        w_index = 0;    
        while(w_index < 7) 
        {
	  // <s,11,20> = <s,5,10> * <s,5,10>
	   w_temp1 = w_rec_real*w_real;
	   w_temp2 = w_rec_imag*w_imag;

          // <s,11,20> = <s,5,10> * <s,5,10>
	   w_temp3 = w_rec_real*w_imag;
	   w_temp4 = w_rec_imag*w_real;	 

	  // <s,6,10> = <s,5,10> - <s,5,10>
           w_temp5 = w_temp1 - w_temp2;

	  // <s,6,10> = <s,5,10> + <s,5,10>
	   w_temp6 = w_temp3 + w_temp4;
	   
	  // assign the sign-bit(MSB)
           W_real[w_index][15] = w_temp5[32];
           W_imag[w_index][15] = w_temp6[32];

	  // assign the rest of the bits
           W_real[w_index].range(14,0) = w_temp5.range(24,10);
           W_imag[w_index].range(14,0) = w_temp6.range(24,10);

	  // update w_rec.. values for the next iteration
	   w_rec_real = W_real[w_index];
	   w_rec_imag = W_imag[w_index];

	   w_index++;

        }

      //////////////////////////////////////////////////////////////////////////
      ///  Computation - 1D Complex DFT In-Place DIF Computation Algorithm  ////
      //////////////////////////////////////////////////////////////////////////

       stage = 0;
       len = N;
       incr = 1;

       while (stage < M) 
       { 
	 len = len >> 1;
 
        //First Iteration :  Simple calculation, with no multiplies
          i = 0;
          while(i < (short)N)  
          {
             index =  i; index2 = i + (short)len; 

             tmp_real = real[index] + real[index2];
             tmp_imag = imag[index] + imag[index2];

             real[index2] = (real[index] - real[index2]);
             imag[index2] = (imag[index] - imag[index2]);

             real[index] = tmp_real;
             imag[index] = tmp_imag;
	    
	     i = i + (len << 1);   
          }

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

	      // Read in the data and twiddle factors
	      w_real  = W_real[windex];
	      w_imag  = W_imag[windex];

              real1_in = real[index];
	      imag1_in = imag[index];
              real2_in = real[index2];
	      imag2_in = imag[index2];

              // Call butterfly computation function	     
	      func_butterfly(w_real, w_imag, real1_in, imag1_in, real2_in, imag2_in, real1_out, imag1_out, real2_out, imag2_out);

	      // Store back the results
              real[index]  = real1_out;
              imag[index]  = imag1_out; 
              real[index2] = real2_out;
              imag[index2] = imag2_out; 

              i = i + (len << 1);
            }
            windex = windex + incr;
            j++;
         }
          stage++;
          incr = incr << 1;
       } 
           
     //////////////////////////////////////////////////////////////////////////   
     //Writing out the normalized transform values in bit reversed order
     //////////////////////////////////////////////////////////////////////////

      sc_uint<4> bits_i;
      sc_uint<4> bits_index;
      sc_int<16> real1;
      sc_int<16> imag1;
      bits_i = 0;
      bits_index = 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;
       real1 = real[index];
       imag1 = imag[index];
       out_real.write(real1); 
       out_imag.write(imag1); 
       data_ready.write(true);
       do { wait(); } while ( !(data_ack == true) );
       data_ready.write(false);
       i++;
       wait();
      }
      index = 0; 
      cout << "Done..." << endl;
  }      
}// end entry() function
