/// <summary>
/// Performs the same as GcdBinary(BigInteger, BigInteger)}, but with numbers of 63 bits,
/// represented in positives values of long type.
/// </summary>
///
/// <param name="X">A positive number</param>
/// <param name="Y">A positive number></param>
///
/// <returns>Returns <c>Gcd(X, Y)</c></returns>
internal static long GcdBinary(long X, long Y)
{
// (op1 > 0) and (op2 > 0)
int lsb1 = IntUtils.NumberOfTrailingZeros(X);
int lsb2 = IntUtils.NumberOfTrailingZeros(Y);
int pow2Count = System.Math.Min(lsb1, lsb2);
if (lsb1 != 0)
{
X = IntUtils.URShift(X, lsb1);
}
if (lsb2 != 0)
{
Y = IntUtils.URShift(Y, lsb2);
}
do
{
if (X >= Y)
{
X -= Y;
X = IntUtils.URShift(X, IntUtils.NumberOfTrailingZeros(X));
}
else
{
Y -= X;
Y = IntUtils.URShift(Y, IntUtils.NumberOfTrailingZeros(Y));
}
} while (X != 0);
return(Y << pow2Count);
}