109 lines
3.6 KiB
C#
109 lines
3.6 KiB
C#
//-----------------------------------------------------------------------
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//-----------------------------------------------------------------------
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// file="Exp.cs"
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// Project: StgSharp
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// AuthorGroup: Nitload Space
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// Copyright (c) Nitload Space. All rights reserved.
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//
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// Permission is hereby granted, free of charge, to any person
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// obtaining a copy of this software and associated documentation
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// files (the “Software”), to deal in the Software without restriction,
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// including without limitation the rights to use, copy, modify, merge,
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// publish, distribute, sublicense, and/or sell copies of the Software,
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// and to permit persons to whom the Software is furnished to do so,
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// subject to the following conditions:
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//
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// The above copyright notice and
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// this permission notice shall be included in all copies
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// or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED “AS IS”,
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// WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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// ARISING FROM, OUT OF OR IN CONNECTION WITH
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// THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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//
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//-----------------------------------------------------------------------
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//-----------------------------------------------------------------------
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namespace StgSharp.Math
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{
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public static unsafe partial class Scaler
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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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/*
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* define z = n * 2 ^ m
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* n is between 0 and 0.5
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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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