62 lines
2.5 KiB
C#
62 lines
2.5 KiB
C#
//-----------------------------------------------------------------------
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//-----------------------------------------------------------------------
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// file="Factorial.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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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading.Tasks;
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namespace StgSharp.Math
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{
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public static partial class Scaler
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{
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private static readonly uint[] factorialResult = [1, 1, 2, 6, 24,120,720,5040,40320,362880,3628800,39916800,479001600];
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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 InternalIO.Intrinsic.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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