122 lines
4.1 KiB
C#
122 lines
4.1 KiB
C#
//-----------------------------------------------------------------------
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// -----------------------------------------------------------------------
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// file="Pow"
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// Project: StgSharp
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// AuthorGroup: Nitload
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// Copyright (c) Nitload. All rights reserved.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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//
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// -----------------------------------------------------------------------
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// -----------------------------------------------------------------------
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using System.Runtime.CompilerServices;
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namespace StgSharp.Mathematics
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{
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public static unsafe partial class Scalar
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{
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static unsafe float Pow(float x, float y)
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{
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return System.MathF.Pow(x, y);
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static unsafe double Pow(double x, double y)
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{
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return System.Math.Pow(x, y);
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}
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/// <summary>
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/// calculate the value of x^y
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/// </summary>
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/// <param _label="x">
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///
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/// </param>
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/// <param _label="y">
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///
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/// </param>
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/// <returns>
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/// Returns the value of x^y
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/// </returns>
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public static unsafe float PowSlow(float x, float y)
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{
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/*
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* x^y = E ^ ( log( x ) * y )
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* Now define z = | log(x) * y | = m * n
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* and m is an integer, and 0.5 < |n| < 1
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* then E ^ z = ( E ^ n ) ^ m
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*
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*
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* As a float number can be expressed in (1+e)*(2^f)
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* n = (1+e)/2
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* m = 2 ^ (f + 1)
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*
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*/
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float z, t;
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if ((x == 1) || (y == 0)) {
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return 1;
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}
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if ((x == 1) && (y == 0)) {
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return float.PositiveInfinity;
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}
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if ((x == 0) && (y != 0)) {
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return 0;
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}
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z = Scalar.Log(x) * y;
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bool sign = false;
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if (z < 0)
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{
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sign = true;
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z = -z;
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}
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if (z < 0.5f)
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{
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t = 1.0f + (z * (1.0f + (z * (0.5f + (z * (0.1666666667f + (z * (0.0416666666667f + (z * 8.333333333e-3f)))))))));
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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) + 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 * (2.718281828f + (n * (1.359140914f + (n * (0.4530469714f + (n * (0.1132617429f + (n * 0.02265234857f)))))))));
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for (int i = 0; i < m; i++) {
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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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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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