using System;
using System.Diagnostics;

namespace fastexponent
{
	class Program
	{
		static double FastExp(double x)
		{
			var tmp = (long)(1512775 * x + 1072632447);
			return BitConverter.Int64BitsToDouble(tmp << 32);
		}

		static void Main(string[] args)
		{
			double[] x = new double[1000000];
			double[] ex = new double[x.Length];
			double[] fx = new double[x.Length];
			Random r = new Random();
			for (int i = 0; i < x.Length; ++i)
				x[i] = r.NextDouble() * 40;

			Stopwatch sw = new Stopwatch();
			sw.Start();
			for (int j = 0; j < x.Length; ++j)
				ex[j] = Math.Exp(x[j]);
			sw.Stop();
			double builtin = sw.Elapsed.TotalMilliseconds;
			sw.Reset();
			sw.Start();
			for (int k = 0; k < x.Length; ++k)
				fx[k] = FastExp(x[k]);
			sw.Stop();
			double custom = sw.Elapsed.TotalMilliseconds;

			double min = 1, max = 1;
			for (int m = 0; m < x.Length; ++m) {
				double ratio = fx[m] / ex[m];
				if (min > ratio) min = ratio;
				if (max < ratio) max = ratio;
			}

			Console.WriteLine("minimum ratio = " + min.ToString() + ", maximum ratio = " + max.ToString() + ", speedup = " + (builtin / custom).ToString());
		 }
	}
}