internal static double CosPi(double x)
{
long y0;
double y1;
RangeReduction.ReduceByOnes(2.0 * x, out y0, out y1);
return(RangeReduction.Cos(y0, y1));
}
internal static double TanPi(double x)
{
RangeReduction.ReduceByOnes(2.0 * x, out long y0, out double y1);
if (y0 % 2L == 0L)
{
return(Math.Tan(Math.PI / 2.0 * y1));
}
else
{
return(-1.0 / Math.Tan(Math.PI / 2.0 * y1));
}
// Should be possible to do even better, by reducing wrt pi / 4, but this is good enough for now.
}
/// <summary>
/// Computes the cosine of the given multiple of π.
/// </summary>
/// <param name="x">The argument.</param>
/// <returns>The value of cos(<paramref name="x"/>π).</returns>
/// <remarks>
/// <para>For an explanation of why and when to use this function,
/// see <see cref="SinPi(double)"/>.</para>
/// </remarks>
/// <seealso cref="SinPi(double)"/>
public static double CosPi(double x)
{
RangeReduction.ReduceByOnes(2.0 * x, out long y0, out double y1);
return(RangeReduction.Cos(y0, y1));
}