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  1. using System;
  2. using System.Diagnostics;
  3.  
  4. namespace fastexponent
  5. {
  6. 	class Program
  7. 	{
  8. 		static double FastExp(double x)
  9. 		{
  10. 			var tmp = (long)(1512775 * x + 1072632447);
  11. 			return BitConverter.Int64BitsToDouble(tmp << 32);
  12. 		}
  13.  
  14. 		static void Main(string[] args)
  15. 		{
  16. 			double[] x = new double[1000000];
  17. 			double[] ex = new double[x.Length];
  18. 			double[] fx = new double[x.Length];
  19. 			Random r = new Random();
  20. 			for (int i = 0; i < x.Length; ++i)
  21. 				x[i] = r.NextDouble() * 40;
  22.  
  23. 			Stopwatch sw = new Stopwatch();
  24. 			sw.Start();
  25. 			for (int j = 0; j < x.Length; ++j)
  26. 				ex[j] = Math.Exp(x[j]);
  27. 			sw.Stop();
  28. 			double builtin = sw.Elapsed.TotalMilliseconds;
  29. 			sw.Reset();
  30. 			sw.Start();
  31. 			for (int k = 0; k < x.Length; ++k)
  32. 				fx[k] = FastExp(x[k]);
  33. 			sw.Stop();
  34. 			double custom = sw.Elapsed.TotalMilliseconds;
  35.  
  36. 			double min = 1, max = 1;
  37. 			for (int m = 0; m < x.Length; ++m) {
  38. 				double ratio = fx[m] / ex[m];
  39. 				if (min > ratio) min = ratio;
  40. 				if (max < ratio) max = ratio;
  41. 			}
  42.  
  43. 			Console.WriteLine("minimum ratio = " + min.ToString() + ", maximum ratio = " + max.ToString() + ", speedup = " + (builtin / custom).ToString());
  44. 		 }
  45. 	}
  46. }
  47.  
Success #stdin #stdout 0.4s 79936KB
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minimum ratio = 0.960597678477954, maximum ratio = 1.01965903274147, speedup = 0.295571114757978
https://ideone.com/HDcMF
language:
C# (gmcs 5.20.1)
created:
12 years ago
visibility:
public

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