63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
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/* _Exp function */
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#include "wctype.h"
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#include "xmath.h"
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_STD_BEGIN
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/* coefficients */
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static const double p[] = { /* courtesy Dr. Tim Prince */
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1.0,
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420.30235984910635,
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15132.70094680474802};
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static const double q[] = { /* courtesy Dr. Tim Prince */
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30.01511290683317,
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3362.72154416553028,
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30265.40189360949691};
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static const double c1 = 22713.0 / 32768.0;
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static const double c2 = 1.428606820309417232e-6L;
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static const double hugexp = HUGE_EXP;
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static const double invln2 = 1.4426950408889634074L;
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_CRTIMP2 short __cdecl _Exp(double *px, double y, short eoff)
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{ /* compute y*e^(*px), (*px) finite, |y| not huge */
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if (*px < -hugexp || y == 0)
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{ /* certain underflow */
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*px = 0;
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return (0);
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}
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else if (hugexp < *px)
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{ /* certain overflow */
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*px = _Inf._D;
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return (INF);
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}
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else
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{ /* xexp won't overflow */
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double g = *px * invln2;
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short xexp = g + (g < 0 ? - 0.5 : + 0.5);
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g = xexp;
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g = (*px - g * c1) - g * c2;
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if (-_Eps._D < g && g < _Eps._D)
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*px = y;
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else
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{ /* g*g worth computing */
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const double z = g * g;
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const double w = (q[0] * z + q[1]) * z + q[2];
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g *= (z + p[1]) * z + p[2];
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*px = (w + g) / (w - g) * 2 * y;
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--xexp;
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}
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return (_Dscale(px, (long)xexp + eoff));
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}
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}
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_STD_END
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/*
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* Copyright (c) 1994 by P.J. Plauger. ALL RIGHTS RESERVED.
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* Consult your license regarding permissions and restrictions.
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*/
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/*
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941029 pjp: added _STD machinery
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*/
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