94 lines
2.3 KiB
C#
94 lines
2.3 KiB
C#
//
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//
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// some of the code is rewritten from the AMD code:
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// https://github.com/amd/aocl-libm-ose/blob/a43e092b03213eb0e129a1cc129900e6e4475778/src/ref/asinf.c
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using System;
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using System.Collections.Generic;
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using System.Text;
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namespace StgSharp
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{
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public static unsafe partial class Math
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{
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private const float
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piby2_tail = 7.5497894159e-08f, /* 0x33a22168 */
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hpiby2_head = 7.8539812565e-01f, /* 0x3f490fda */
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piby2 = 1.5707963705e+00f; /* 0x3fc90fdb */
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/// <summary>
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/// Reurns the value of ArcSin(x)
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/// </summary>
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/// <param name="x"></param>
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/// <returns></returns>
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/// <exception cref="ArgumentException"></exception>
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public static float ASin(float x )
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{
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int sign = 1;
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float y ;
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if (x<0)
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{
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sign = -1;
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y = -x;
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}
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else
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{
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y = x;
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}
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if ( x>1)
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{
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throw new ArgumentException();
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}
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float r, s, u, v = 0.0f;
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bool transform = (y >= 0.5f);
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if (transform)
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{
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r = 0.5f * (1.0f - y);
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s = StgSharp.Math.Sqrt(r);
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y = s;
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}
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else
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{
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r = y * y;
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}
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u= r * (0.184161606965100694821398249421F +
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(-0.0565298683201845211985026327361F +
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(-0.0133819288943925804214011424456F -
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0.00396137437848476485201154797087F * r) * r) * r) /
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(1.10496961524520294485512696706F -
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0.836411276854206731913362287293F * r);
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/**/
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if (transform)
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{
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float c, s1, p, q;
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uint us;
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us = *(uint*)&s;
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uint uss = us & 0xffff0000;
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s1 = *(float*)&uss;
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c = (r - s1 * s1) / (s + s1);
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p = 2.0F * s * u - (piby2_tail - 2.0F * c);
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q = hpiby2_head - 2.0F * s1;
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v = hpiby2_head - (p - q);
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}
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else
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{
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v = y + y * u;
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}/**/
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return sign * v * 90 / piby2;
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}
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}
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}
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