Multiply instead of divide

[jonassix]

    public static void Divide(out Int128 c, ref Int128 a, int b)
        {
            if (a.IsNegative)
            {
                UInt128 aneg;
                UInt128.Negate(out aneg, ref a.v);
                if (b < 0)
                    UInt128.Multiply(out c.v, ref aneg, (uint)(-b));
                else
                {
                    UInt128.Multiply(out c.v, ref aneg, (uint)b);
                    UInt128.Negate(ref c.v);
                }
            }
            else
            {
                if (b < 0)
                {
                    UInt128.Multiply(out c.v, ref a.v, (uint)(-b));
                    UInt128.Negate(ref c.v);
                }
                else
                    UInt128.Multiply(out c.v, ref a.v, (uint)b);
            }
            Debug.Assert((BigInteger)c == (BigInteger)a / (BigInteger)b);
        }