How to use IPP FIRGenBandStop method? Following this link:
http://software.intel.com/sites/products/documentation/doclib/ipp_sa/80/ipp_manual/GUID-5457048E-3C59-43E4-8A99-FB3873DCB769.htm
I have produced the following code:

        const int len = 512;
        Ipp64f pInputSignal[len];

        int tapslen = 27;
        int numIters = len;

        IppsFIRState_64f* pState;
        IppStatus status;

        Ipp64f* pOutputSignal = ippsMalloc_64f(len*sizeof(Ipp64f));
        Ipp64f* taps = ippsMalloc_64f(tapslen*sizeof(Ipp64f));
        Ipp64f* pDL = ippsMalloc_64f(tapslen*sizeof(Ipp64f));

        ippsZero_64f(pDL,tapslen);
        float sample_rate = 48000.0;//Hz //TODO DEFAULT_SAMPLE_RATE
        float frequency = 400.0;//Hz
        float amplitude = 2000.0;

        //Fill pInputSignal[t] = 2*pi*frequency*t, where t is time from t[i] = i/sample_rate
        fillBufferWithSinusoidData_64f(pInputSignal,len,sample_rate,frequency,amplitude);

        //computes tapsLen coefficients for bandstop  FIR filter
        float rFreqLow  = (frequency-52.0)/(sample_rate);
        float rFreqHigh = (frequency+51.0)/(sample_rate);

        status = ippsFIRGenBandstop_64f(
            rFreqLow,
            rFreqHigh,
            taps, 
            tapslen, 
            ippWinHamming, 
            ippTrue);
        Assert::AreEqual((int)IppStatus::ippStsNoErr,(int)status);

        ////filter an input vector
        status = ippsFIRInitAlloc_64f(&amp;pState, taps,tapslen, pDL);
        status = ippsFIR_64f(pInputSignal, pOutputSignal, numIters, pState);


In other words: 
Input is a sinusoid at frequency 400Hz
Band stop between 348.0Hz to 451Hz

Expected output : something flat (as I would expect the sine signal would get filtered out).

Actual output : Sine wave moves 1/2 phase, magnitude is lowered a bit. 

Any ideas about what went wrong here?
There are some issues with the code.
1. There seems to be a problem number of taps used for frequency. For filtering 400Hz sine wave at samplerate 48KHz I get better results if I use tapslen more than 559. 
2. ippsFIRGenBandstop apparently is implemented as band pass + band stop + band pass. By doing this IPP tends to add some ripple at the higher end (around 44,000 and above). See here:


When using this filter it is recommended to use some kind of a FIR filter design tool like TFilter: http://t-filter.appspot.com/fir/index.html
Or matlab FIR filter design toolbox.