Implementing if-else with __m64 data types

.h file
 class tom
{
.
.
.
protected:
    static const int Adjust[6];

protected:
    int _mode;

    int _q;
    int _qm;
    int _qe;
    int _f;
    int _scale
};

.cpp file
const int tom::Adjust[6] =
{
    107,
    916,
    182,
    362,
    192,
    282
};

tom::tom()
{

    _q          = 1;
     _qm        =_q % 6;
    _qe         = _q/6;
    _f          = (1 << (15+_qe))/6;
    _scale  = 15+_qe;
}

void tom::calculate(void* ptr)
{
    short* block = (short *)ptr;
    int j;

     __m64*block1 = (__m64*)block;
     __m64 s0,s1,s2,s3,x0,x1,x2,x3;
      j=0;
        //step 1
s0 =_mm_add_pi16(block1[j],block1[j+3]);
s3 =_mm_sub_pi16(block1[j],block1[j+3]);
s1 =_mm_add_pi16(block1[j+1],block1[j+2]);
s2 =_mm_sub_pi16(block1[j+1],block1[j+2]);

      // step 2
 x0 =_mm_add_pi16(s0,s1);
 if(x0 < 0)
block[j] = (short)(-( (((-x0) * Adjust[_qm]) + _f) >> _scale ));
else
block[j] = (short)( ((x0 * Adjust[_qm]) + _f) >> _scale );
.
.
.
.

_mm_empty();

}