text: #include "huffman.h"
  // Postcondition: out[x].frequency > 0
  void filter(
              /* input  */ Symbol in[INPUT_SYMBOL_SIZE],
              /* output */ Symbol out[INPUT_SYMBOL_SIZE],
              /* output */ int *n) {
  #pragma HLS INLINE off
      ap_uint<SYMBOL_BITS> j = 0;
      for(int i = 0; i < INPUT_SYMBOL_SIZE; i++) {
  #pragma HLS pipeline II=1
          if(in[i].frequency != 0) {
              out[j].frequency = in[i].frequency;
              out[j].value = in[i].value;
              j++;
          }
      }
      *n = j;
  }
  