anchor.diff:  
         Bit #(64) res = signExtend(pack (v));
         let fcsr = exception_to_fcsr(e);
  -      fa_driveResponse (res, fcsr);
         resultR     <= tagged Valid (tuple2 (res, fcsr));
         stateR      <= FBOX_RSP;
      endrule
  
positive.code:       if ( isSNaN (sV1) || isSNaN (sV2) ) e.invalid_op = True;
        let fcsr = exception_to_fcsr(e);
  
        fa_driveResponse (res, fcsr);
        resultR     <= tagged Valid (tuple2 (res, fcsr));
        stateR      <= FBOX_RSP;
     endrule
  
     rule doFMV_W_X ( validReq && isFMV_W_X );
        Bit #(64) res = fv_nanbox (pack ( v1 ));
        fa_driveResponse (res, 0);
        resultR     <= tagged Valid (tuple2 (res, 0));
        stateR      <= FBOX_RSP;
     endrule
  
negative.code:       if (isNaN(sV1) || isNaN(sV2)) e.invalid_op = True;
        let fcsr = exception_to_fcsr(e);
  
        resultR     <= tagged Valid (tuple2 (res, fcsr));
        stateR      <= FBOX_RSP;
     endrule
  