77 lines
1.9 KiB
C#
77 lines
1.9 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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namespace StgSharp.Math
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{
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public static unsafe partial class Calc
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{
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public const float E = 2.718281828f;
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/// <summary>
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/// Get the value of E ^ x;
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/// </summary>
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/// <param name="x"></param>
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/// <returns></returns>
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public static unsafe float Exp(float x)
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{
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if (x == 1)
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{
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return E;
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}
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if (x == 0)
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{
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return 1;
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}
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bool sign = false;
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if (x<0)
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{
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sign = true;
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x = -x;
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}
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float z = x , t;
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if (x<0.5f)
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{
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t = 1.0f + x * (
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1.0f + x * (
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0.5f + x * (
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0.1666666667f + x * (
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0.0416666666667f + x *
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8.333333333e-3f))));
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}
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else
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{
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uint zBit = *(uint*)&z;
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uint zBitAbs = zBit & 0b_0111_1111_1111_1111_1111_1111_1111_1111;
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uint uintm = (zBitAbs >> 23);
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int m = (*(int*)&uintm) - 126;
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uint nBit = (zBitAbs & 0b_0000_0000_0111_1111_1111_1111_1111_1111)
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+ 0b_0011_1111_0000_0000_0000_0000_0000_0000;
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float n = *(float*)&nBit - 1;
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t = 2.718281828f + n * (
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2.718281828f + n * (
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1.359140914f + n * (
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0.4530469714f + n * (
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0.1132617429f + n *
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0.02265234857f))));
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for (int i = 0; i < m; i++)
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{
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t = t * t;
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}
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}
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if (sign)
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{
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t = 1 / t;
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}
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return t;
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}
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}
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}
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