級数展開でcosの近似値を出すテスト

CosApproximate.cs

// https://twitter.com/TEST_H_/status/1023975602494169092

using System;
using System.Diagnostics; 

namespace MyContents
{
    class Test
    {
        static void Main() 
        {
            Stopwatch sw = new Stopwatch(); 
            sw.Start();
            
            for(int i = 0; i < 360; ++i)
            {
                float rad = i * ((3.14f * 2) / 360f);
#if false
                float ret = 1 - (Pow(rad, 2) / 2)
                            + (Pow(rad, 4) / Factorial(4))
                            - (Pow(rad, 6) / Factorial(6))
                            + (Pow(rad, 8) / Factorial(8));
                
#else
                // 高速版
                float pow1 = rad * rad;
                float pow2 = pow1 * pow1;
                float pow3 = pow2 * pow1;
                float pow4 = pow2 * pow2;
                float ret = 1 - (pow1 / 2f)
                            + (pow2 / 24f)        // 4!
                            - (pow3 / 720f)       // 6!
                            + (pow4 / 40320f);    // 8!
#endif
                
                Console.WriteLine(ret);
            }
            sw.Stop();
            Console.WriteLine("Elapsed = {0}", sw.Elapsed); 
        }
        
        static float Pow(float x, float y)
        {
            return (float)Math.Pow((double)x, (double)y);
        }
        
        static int Factorial(int n)
        {
            int x = 1;
            while(n > 1)
            {
                x = x * n;
                n--;
            }
            return x;
        }
    }
}