MARKUS

// (c) Copyright Microsoft Corporation.

// This source is subject to the Microsoft Public License (Ms-PL).

// Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.

// All other rights reserved.

using System;

using System.Diagnostics.CodeAnalysis;

using System.Runtime.InteropServices;

namespace System.Windows.Controls

{

    /// <summary>

    /// Numeric utility methods used by controls.  These methods are similar in

    /// scope to the WPF DoubleUtil class.

    /// </summary>

    internal static class NumericExtensions

    {

        /// <summary>

        /// NanUnion is a C++ style type union used for efficiently converting

        /// a double into an unsigned long, whose bits can be easily

        /// manipulated.

        /// </summary>

        [StructLayout(LayoutKind.Explicit)]

        private struct NanUnion

        {

            /// <summary>

            /// Floating point representation of the union.

            /// </summary>

            [SuppressMessage("Microsoft.Performance", "CA1823:AvoidUnusedPrivateFields", Justification = "It is accessed through the other member of the union")]

            [FieldOffset(0)]

            internal double FloatingValue;

            /// <summary>

            /// Integer representation of the union.

            /// </summary>

            [FieldOffset(0)]

            internal ulong IntegerValue;

        }

        /// <summary>

        /// Check if a number is zero.

        /// </summary>

        /// <param name="value">The number to check.</param>

        /// <returns>True if the number is zero, false otherwise.</returns>

        public static bool IsZero(this double value)

        {

            // We actually consider anything within an order of magnitude of

            // epsilon to be zero

            return Math.Abs(value) < 2.2204460492503131E-15;

        }

        /// <summary>

        /// Check if a number isn't really a number.

        /// </summary>

        /// <param name="value">The number to check.</param>

        /// <returns>

        /// True if the number is not a number, false if it is a number.

        /// </returns>

        public static bool IsNaN(this double value)

        {

            // Get the double as an unsigned long

            NanUnion union = new NanUnion { FloatingValue = value };

            // An IEEE 754 double precision floating point number is NaN if its

            // exponent equals 2047 and it has a non-zero mantissa.

            ulong exponent = union.IntegerValue & 0xfff0000000000000L;

            if ((exponent != 0x7ff0000000000000L) && (exponent != 0xfff0000000000000L))

            {

                return false;

            }

            ulong mantissa = union.IntegerValue & 0x000fffffffffffffL;

            return mantissa != 0L;

        }

        /// <summary>

        /// Determine if one number is greater than another.

        /// </summary>

        /// <param name="left">First number.</param>

        /// <param name="right">Second number.</param>

        /// <returns>

        /// True if the first number is greater than the second, false

        /// otherwise.

        /// </returns>

        public static bool IsGreaterThan(double left, double right)

        {

            return (left > right) && !AreClose(left, right);

        }

        /// <summary>

        /// Determine if one number is less than or close to another.

        /// </summary>

        /// <param name="left">First number.</param>

        /// <param name="right">Second number.</param>

        /// <returns>

        /// True if the first number is less than or close to the second, false

        /// otherwise.

        /// </returns>

        public static bool IsLessThanOrClose(double left, double right)

        {

            return (left < right) || AreClose(left, right);

        }

        /// <summary>

        /// Determine if two numbers are close in value.

        /// </summary>

        /// <param name="left">First number.</param>

        /// <param name="right">Second number.</param>

        /// <returns>

        /// True if the first number is close in value to the second, false

        /// otherwise.

        /// </returns>

        public static bool AreClose(double left, double right)

        {

            if (left == right)

            {

                return true;

            }

            double a = (Math.Abs(left) + Math.Abs(right) + 10.0) * 2.2204460492503131E-16;

            double b = left - right;

            return (-a < b) && (a > b);

        }

    }

}