68 lines
2.5 KiB
C#
68 lines
2.5 KiB
C#
//-----------------------------------------------------------------------
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// -----------------------------------------------------------------------
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// file="Factorial"
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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 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;
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namespace StgSharp.Mathematics
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{
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public static partial class Scalar
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{
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private static readonly uint[] factorialResult = [
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1,
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1,
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2,
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6,
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24,
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120,
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720,
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5040,
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40320,
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362880,
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3628800,
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39916800,
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479001600];
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public static unsafe ulong Factorial(int n)
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{
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ArgumentOutOfRangeException.ThrowIfLessThan(n, 0);
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if (n < 13) {
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return factorialResult[n];
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}
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if (n < 30) {
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return NumericalModule.GlobalContext.factorial_simd(n);
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}
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double
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dn = n,
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stir = Sqrt(2 * PiDouble * dn) * Pow(dn / EDouble, dn),
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correction = Exp(1 / (12 * dn));
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return (ulong)(stir * correction);
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}
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}
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}
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