set library 1;

// pseudo classic operator to swap bit order

cond qufunct flip(qureg q) { 
  int i;                // declare loop counter
  for i=0 to #q/2-1 {   // swap 2 symmetric bits
    Swap(q[i],q[#q-i-1]);
  }
}  

// discrete Fourier transform (Coppersmith)

operator dft(qureg q) { // main operator
  const n=#q;           // set n to length of input
  int i; int j;         // declare loop counters
  for i=1 to n {
    for j=1 to i-1 {    // apply conditional phase gates
      V(pi/2^(i-j),q[n-i] & q[n-j]);
//      if q[n-i] and q[n-j] { Phase(pi/2^(i-j)); }
    }
    H(q[n-i]);          // qubit rotation
  }    
  flip(q);              // swap bit order of the output
}

set library 0;