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  1. using System;
  2. using System.Diagnostics;
  3.  
  4. namespace fastexponent
  5. {
  6. 	class Program
  7. 	{
  8. 		static double[] ExpAdjustment = new double[256] {
  9. 			1.040389835,
  10. 			1.039159306,
  11. 			1.037945888,
  12. 			1.036749401,
  13. 			1.035569671,
  14. 			1.034406528,
  15. 			1.033259801,
  16. 			1.032129324,
  17. 			1.031014933,
  18. 			1.029916467,
  19. 			1.028833767,
  20. 			1.027766676,
  21. 			1.02671504,
  22. 			1.025678708,
  23. 			1.02465753,
  24. 			1.023651359,
  25. 			1.022660049,
  26. 			1.021683458,
  27. 			1.020721446,
  28. 			1.019773873,
  29. 			1.018840604,
  30. 			1.017921503,
  31. 			1.017016438,
  32. 			1.016125279,
  33. 			1.015247897,
  34. 			1.014384165,
  35. 			1.013533958,
  36. 			1.012697153,
  37. 			1.011873629,
  38. 			1.011063266,
  39. 			1.010265947,
  40. 			1.009481555,
  41. 			1.008709975,
  42. 			1.007951096,
  43. 			1.007204805,
  44. 			1.006470993,
  45. 			1.005749552,
  46. 			1.005040376,
  47. 			1.004343358,
  48. 			1.003658397,
  49. 			1.002985389,
  50. 			1.002324233,
  51. 			1.001674831,
  52. 			1.001037085,
  53. 			1.000410897,
  54. 			0.999796173,
  55. 			0.999192819,
  56. 			0.998600742,
  57. 			0.998019851,
  58. 			0.997450055,
  59. 			0.996891266,
  60. 			0.996343396,
  61. 			0.995806358,
  62. 			0.995280068,
  63. 			0.99476444,
  64. 			0.994259393,
  65. 			0.993764844,
  66. 			0.993280711,
  67. 			0.992806917,
  68. 			0.992343381,
  69. 			0.991890026,
  70. 			0.991446776,
  71. 			0.991013555,
  72. 			0.990590289,
  73. 			0.990176903,
  74. 			0.989773325,
  75. 			0.989379484,
  76. 			0.988995309,
  77. 			0.988620729,
  78. 			0.988255677,
  79. 			0.987900083,
  80. 			0.987553882,
  81. 			0.987217006,
  82. 			0.98688939,
  83. 			0.98657097,
  84. 			0.986261682,
  85. 			0.985961463,
  86. 			0.985670251,
  87. 			0.985387985,
  88. 			0.985114604,
  89. 			0.984850048,
  90. 			0.984594259,
  91. 			0.984347178,
  92. 			0.984108748,
  93. 			0.983878911,
  94. 			0.983657613,
  95. 			0.983444797,
  96. 			0.983240409,
  97. 			0.983044394,
  98. 			0.982856701,
  99. 			0.982677276,
  100. 			0.982506066,
  101. 			0.982343022,
  102. 			0.982188091,
  103. 			0.982041225,
  104. 			0.981902373,
  105. 			0.981771487,
  106. 			0.981648519,
  107. 			0.981533421,
  108. 			0.981426146,
  109. 			0.981326648,
  110. 			0.98123488,
  111. 			0.981150798,
  112. 			0.981074356,
  113. 			0.981005511,
  114. 			0.980944219,
  115. 			0.980890437,
  116. 			0.980844122,
  117. 			0.980805232,
  118. 			0.980773726,
  119. 			0.980749562,
  120. 			0.9807327,
  121. 			0.9807231,
  122. 			0.980720722,
  123. 			0.980725528,
  124. 			0.980737478,
  125. 			0.980756534,
  126. 			0.98078266,
  127. 			0.980815817,
  128. 			0.980855968,
  129. 			0.980903079,
  130. 			0.980955475,
  131. 			0.981017942,
  132. 			0.981085714,
  133. 			0.981160303,
  134. 			0.981241675,
  135. 			0.981329796,
  136. 			0.981424634,
  137. 			0.981526154,
  138. 			0.981634325,
  139. 			0.981749114,
  140. 			0.981870489,
  141. 			0.981998419,
  142. 			0.982132873,
  143. 			0.98227382,
  144. 			0.982421229,
  145. 			0.982575072,
  146. 			0.982735318,
  147. 			0.982901937,
  148. 			0.983074902,
  149. 			0.983254183,
  150. 			0.983439752,
  151. 			0.983631582,
  152. 			0.983829644,
  153. 			0.984033912,
  154. 			0.984244358,
  155. 			0.984460956,
  156. 			0.984683681,
  157. 			0.984912505,
  158. 			0.985147403,
  159. 			0.985388349,
  160. 			0.98563532,
  161. 			0.98588829,
  162. 			0.986147234,
  163. 			0.986412128,
  164. 			0.986682949,
  165. 			0.986959673,
  166. 			0.987242277,
  167. 			0.987530737,
  168. 			0.987825031,
  169. 			0.988125136,
  170. 			0.98843103,
  171. 			0.988742691,
  172. 			0.989060098,
  173. 			0.989383229,
  174. 			0.989712063,
  175. 			0.990046579,
  176. 			0.990386756,
  177. 			0.990732574,
  178. 			0.991084012,
  179. 			0.991441052,
  180. 			0.991803672,
  181. 			0.992171854,
  182. 			0.992545578,
  183. 			0.992924825,
  184. 			0.993309578,
  185. 			0.993699816,
  186. 			0.994095522,
  187. 			0.994496677,
  188. 			0.994903265,
  189. 			0.995315266,
  190. 			0.995732665,
  191. 			0.996155442,
  192. 			0.996583582,
  193. 			0.997017068,
  194. 			0.997455883,
  195. 			0.99790001,
  196. 			0.998349434,
  197. 			0.998804138,
  198. 			0.999264107,
  199. 			0.999729325,
  200. 			1.000199776,
  201. 			1.000675446,
  202. 			1.001156319,
  203. 			1.001642381,
  204. 			1.002133617,
  205. 			1.002630011,
  206. 			1.003131551,
  207. 			1.003638222,
  208. 			1.00415001,
  209. 			1.004666901,
  210. 			1.005188881,
  211. 			1.005715938,
  212. 			1.006248058,
  213. 			1.006785227,
  214. 			1.007327434,
  215. 			1.007874665,
  216. 			1.008426907,
  217. 			1.008984149,
  218. 			1.009546377,
  219. 			1.010113581,
  220. 			1.010685747,
  221. 			1.011262865,
  222. 			1.011844922,
  223. 			1.012431907,
  224. 			1.013023808,
  225. 			1.013620615,
  226. 			1.014222317,
  227. 			1.014828902,
  228. 			1.01544036,
  229. 			1.016056681,
  230. 			1.016677853,
  231. 			1.017303866,
  232. 			1.017934711,
  233. 			1.018570378,
  234. 			1.019210855,
  235. 			1.019856135,
  236. 			1.020506206,
  237. 			1.02116106,
  238. 			1.021820687,
  239. 			1.022485078,
  240. 			1.023154224,
  241. 			1.023828116,
  242. 			1.024506745,
  243. 			1.025190103,
  244. 			1.02587818,
  245. 			1.026570969,
  246. 			1.027268461,
  247. 			1.027970647,
  248. 			1.02867752,
  249. 			1.029389072,
  250. 			1.030114973,
  251. 			1.030826088,
  252. 			1.03155163,
  253. 			1.032281819,
  254. 			1.03301665,
  255. 			1.033756114,
  256. 			1.034500204,
  257. 			1.035248913,
  258. 			1.036002235,
  259. 			1.036760162,
  260. 			1.037522688,
  261. 			1.038289806,
  262. 			1.039061509,
  263. 			1.039837792,
  264. 			1.040618648
  265. 		};
  266.  
  267. 		static double FastExp(double x)
  268. 		{
  269. 			var tmp = (long)(1512775 * x + 1072632447);
  270. 			int index = (int)(tmp >> 12) & 0xFF;
  271. 			return BitConverter.Int64BitsToDouble(tmp << 32) * ExpAdjustment[index];
  272. 		}
  273.  
  274. 		static void Main(string[] args)
  275. 		{
  276. 			double[] x = new double[1000000];
  277. 			double[] ex = new double[x.Length];
  278. 			double[] fx = new double[x.Length];
  279. 			Random r = new Random();
  280. 			for (int i = 0; i < x.Length; ++i)
  281. 				x[i] = r.NextDouble() * 40;
  282.  
  283. 			Stopwatch sw = new Stopwatch();
  284. 			sw.Start();
  285. 			for (int j = 0; j < x.Length; ++j)
  286. 				ex[j] = Math.Exp(x[j]);
  287. 			sw.Stop();
  288. 			double builtin = sw.Elapsed.TotalMilliseconds;
  289. 			sw.Reset();
  290. 			sw.Start();
  291. 			for (int k = 0; k < x.Length; ++k)
  292. 				fx[k] = FastExp(x[k]);
  293. 			sw.Stop();
  294. 			double custom = sw.Elapsed.TotalMilliseconds;
  295.  
  296. 			double min = 1, max = 1;
  297. 			for (int m = 0; m < x.Length; ++m) {
  298. 				double ratio = fx[m] / ex[m];
  299. 				if (min > ratio) min = ratio;
  300. 				if (max < ratio) max = ratio;
  301. 			}
  302.  
  303. 			Console.WriteLine("minimum ratio = " + min.ToString() + ", maximum ratio = " + max.ToString() + ", speedup = " + (builtin / custom).ToString());
  304. 		 }
  305. 	}
  306. }
  307.  
Success #stdin #stdout 0.41s 80192KB
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minimum ratio = 0.999397250057029, maximum ratio = 1.0005929587234, speedup = 0.272655868851219
https://ideone.com/UwNgx
language:
C# (gmcs 5.20.1)
created:
12 years ago
visibility:
public

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