mathhelper1.cs

用c#编写的任意项傅立叶变换和2的n次项快速傅立叶变换的算法。

namespace Mymath
{
    using System;

    public static class MathHelper
    {
        /// <summary>
        /// Calculates power of 2
        /// </summary>
        /// <param name="power">Power</param>
        /// <returns>Returns specified power of 2 in the case if power is in the range of  [0, 30]. Otherwise returns 0.</returns>
        public static int Pow2(int power)
        {
            return ((power >= 0) && (power <= 30)) ? (1 << power) : 0;
        }

        /// <summary>
        /// Checks if the specified integer is power of 2
        /// </summary>
        /// <param name="x">Integer number to check</param>
        /// <returns>Returns <b>true</b> if the specified number is power of 2.
        /// Otherwise returns <b>false</b>.</returns>
        public static bool IsPowerOf2(int x)
        {
            return (x & (x - 1)) == 0;
        }

        /// <summary>
        /// Get base of binary logarithm
        /// </summary>
        /// <param name="x">Source integer number</param>
        /// <returns>Power of the number (base of binary logarithm).</returns>
        public static int Log2(int x)
        {
            if (x <= 65536)
            {
                if (x <= 256)
                {
                    if (x <= 16)
                    {
                        if (x <= 4)
                        {
                            if (x <= 2)
                            {
                                if (x <= 1)
                                    return 0;
                                return 1;
                            }
                            return 2;
                        }
                        if (x <= 8)
                            return 3;
                        return 4;
                    }
                    if (x <= 64)
                    {
                        if (x <= 32)
                            return 5;
                        return 6;
                    }
                    if (x <= 128)
                        return 7;
                    return 8;
                }
                if (x <= 4096)
                {
                    if (x <= 1024)
                    {
                        if (x <= 512)
                            return 9;
                        return 10;
                    }
                    if (x <= 2048)
                        return 11;
                    return 12;
                }
                if (x <= 16384)
                {
                    if (x <= 8192)
                        return 13;
                    return 14;
                }
                if (x <= 32768)
                    return 15;
                return 16;
            }

            if (x <= 16777216)
            {
                if (x <= 1048576)
                {
                    if (x <= 262144)
                    {
                        if (x <= 131072)
                            return 17;
                        return 18;
                    }
                    if (x <= 524288)
                        return 19;
                    return 20;
                }
                if (x <= 4194304)
                {
                    if (x <= 2097152)
                        return 21;
                    return 22;
                }
                if (x <= 8388608)
                    return 23;
                return 24;
            }
            if (x <= 268435456)
            {
                if (x <= 67108864)
                {
                    if (x <= 33554432)
                        return 25;
                    return 26;
                }
                if (x <= 134217728)
                    return 27;
                return 28;
            }
            if (x <= 1073741824)
            {
                if (x <= 536870912)
                    return 29;
                return 30;
            }
            return 31;
        }
    }
}