// See https://en.wikipedia.org/wiki/Fast_inverse_square_root for more information.
public static double InvSqrt(double x)
{
LongDouble i = new LongDouble(x);
double x2 = x * 0.5, y;
const double threehalfs = 1.5;
i.long_value = inv_sqrt_magic_number_64_bit - (i.long_value >> 1);
y = i.double_value;
y *= threehalfs - (x2 * y * y); // 1st iteration
y *= threehalfs - (x2 * y * y); // 2nd iteration
// y *= threehalfs - (x2 * y * y); // 3nd iteration
return y;
}
/// <summary>
/// Gets the binary representation of the specified double-precision floating point value.
/// </summary>
/// <param name="value">The value to convert to bytes.</param>
/// <returns>The array that stores the binary representation.</returns>
public static byte[] GetBytes( double value )
{
var converter = new LongDouble();
converter.DoubleValue = value;
return GetBytes(converter.LongValue);
}
/// <summary>
/// Gets the double-precision floating point value from the binary representation.
/// </summary>
/// <param name="array">The array that stores the binary representation.</param>
/// <param name="startIndex">The starting position within <paramref name="array"/>.</param>
/// <returns>The value found.</returns>
public static double ToDouble( byte[] array, int startIndex )
{
var converter = new LongDouble();
converter.LongValue = ToInt64(array, startIndex);
return converter.DoubleValue;
}
/// <summary>
/// Gets the binary representation of the specified double-precision floating point value.
/// </summary>
/// <param name="value">The value to convert to bytes.</param>
/// <param name="array">The array that stores the binary representation.</param>
/// <param name="startIndex">The starting position within <paramref name="array"/>.</param>
public static void GetBytes( double value, byte[] array, int startIndex )
{
var converter = new LongDouble();
converter.DoubleValue = value;
GetBytes(converter.LongValue, array, startIndex);
}
