60 lines
1.3 KiB
C
60 lines
1.3 KiB
C
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/* _FExp 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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static const float p[] = { /* courtesy Dr. Tim Prince */
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1.0F,
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60.09114349F};
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static const float q[] = { /* courtesy Dr. Tim Prince */
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12.01517514F,
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120.18228722F};
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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 float hugexp = FHUGE_EXP;
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static const float invln2 = 1.4426950408889634074F;
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_CRTIMP2 short __cdecl _FExp(float *px, float 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 = _FInf._F;
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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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float 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 (-_FEps._F < g && g < _FEps._F)
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*px = y;
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else
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{ /* g*g worth computing */
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const float z = g * g;
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const float w = q[0] * z + q[1];
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g *= z + p[1];
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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 (_FDscale(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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