mathnet-numerics/src/Managed/NumberTheory/IntegerTheory.cs

// <copyright file="IntegerTheory.cs" company="Math.NET">
// Math.NET Numerics, part of the Math.NET Project
// http://mathnet.opensourcedotnet.info
//
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namespace MathNet.Numerics.NumberTheory
{
    using System;

    /// <summary>
    /// Number theory utility functions for integers.
    /// </summary>
    public static class IntegerTheory
    {
        /// <summary>
        /// Find out whether the provided 32 bit integer is an even number.
        /// </summary>
        /// <param name="number">The number to very whether it's even.</param>
        /// <returns>True if and only if it is an even number.</returns>
        public static bool IsEven(this int number)
        {
            return (number & 0x1) == 0x0;
        }

        /// <summary>
        /// Find out whether the provided 64 bit integer is an even number.
        /// </summary>
        /// <param name="number">The number to very whether it's even.</param>
        /// <returns>True if and only if it is an even number.</returns>
        public static bool IsEven(this long number)
        {
            return (number & 0x1) == 0x0;
        }

        /// <summary>
        /// Find out whether the provided 32 bit integer is an odd number.
        /// </summary>
        /// <param name="number">The number to very whether it's odd.</param>
        /// <returns>True if and only if it is an odd number.</returns>
        public static bool IsOdd(this int number)
        {
            return (number & 0x1) == 0x1;
        }

        /// <summary>
        /// Find out whether the provided 64 bit integer is an odd number.
        /// </summary>
        /// <param name="number">The number to very whether it's odd.</param>
        /// <returns>True if and only if it is an odd number.</returns>
        public static bool IsOdd(this long number)
        {
            return (number & 0x1) == 0x1;
        }

        /// <summary>
        /// Find out whether the provided 32 bit integer is a perfect square, i.e. a square of an integer.
        /// </summary>
        /// <param name="number">The number to very whether it's a perfect square.</param>
        /// <returns>True if and only if it is a perfect square.</returns>
        public static bool IsPerfectSquare(int number)
        {
            if (number < 0)
            {
                return false;
            }

            int lastHexDigit = number & 0xF;
            if (lastHexDigit > 9)
            {
                return false; // return immediately in 6 cases out of 16.
            }

            if (lastHexDigit == 0 || lastHexDigit == 1 || lastHexDigit == 4 || lastHexDigit == 9)
            {
                int t = (int)Math.Floor(Math.Sqrt(number) + 0.5);
                return (t * t) == number;
            }

            return false;
        }

        /// <summary>
        /// Find out whether the provided 64 bit integer is a perfect square, i.e. a square of an integer.
        /// </summary>
        /// <param name="number">The number to very whether it's a perfect square.</param>
        /// <returns>True if and only if it is a perfect square.</returns>
        public static bool IsPerfectSquare(long number)
        {
            if (number < 0)
            {
                return false;
            }

            int lastHexDigit = (int)(number & 0xF);
            if (lastHexDigit > 9)
            {
                return false; // return immediately in 6 cases out of 16.
            }

            if (lastHexDigit == 0 || lastHexDigit == 1 || lastHexDigit == 4 || lastHexDigit == 9)
            {
                long t = (long)Math.Floor(Math.Sqrt(number) + 0.5);
                return (t * t) == number;
            }

            return false;
        }
    }
}