Преобразование отрицательного индекса в C в C#

I have to convert my code from c with pointers into c#
code in C is like this 

myMethodName(Word16 exc[],Word16 T0)
{
  Word16 *p_exc;
  Word16 *a;
  a=&(exc[-T0])
  a++;
  b=a;
  c=a;
  a++;
  p_exc = exc;
for (i = 10; i > 0; i--)
{
	s2 += ((Word32) * (b--));
	s1 += ((Word32) * (b));
        s1 += ((Word32) * (c++));
        s2 += ((Word32) * (c));
}
*(p_exc++) = (Word16)(s1 >> 15);
}

I Have tried this
myMethodName(Int16[] exc,Int16 T0)
{
 Int16 pIndex=0;
 Int16 a=0;
 a = T0;
a++;
b=a;
c=a;
for (i = 10; i > 0; i--)
{
	s2 += ((Int32) * (b--));
	s1 += ((Int32) * (b));
        s1 += ((Int32) * (c++));
        s2 += ((Int32) * (c));
}
p_exc[pIndex++] = (Int16)(s1 >> 15);
}