85 lines
2.5 KiB
C
85 lines
2.5 KiB
C
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/* _LExp function */
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#include "xmath.h"
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_STD_BEGIN
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/* coefficients */
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#if _DLONG <= 1 /* assume IEEE 754 10 byte */
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static const long double p[] = { /* courtesy Dr. Tim Prince */
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42.038913947607355L,
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10096.353102778762831L,
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333228.767219512631062L};
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static const long double q[] = { /* courtesy Dr. Tim Prince */
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1.0L,
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841.167880526530790L,
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75730.834075476293976L,
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666457.534439025262146L};
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#else /* assume IEEE 754 16 byte */
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static const long double p[] = { /* courtesy Dr. Tim Prince */
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2.9807566520819951922553427799e-12L,
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1.77137207816625148450390487465e-8L,
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1.5047926518149448268177793026372e-5L,
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3.611828913847589925056132680618007e-3L,
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2.3684088648142335389097476188945590e-1L};
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static const long double q[] = { /* courtesy Dr. Tim Prince */
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3.279723985560247033712687707263e-10L,
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6.1415060072086450089090888123384e-7L,
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2.708775201978218837374512615596512e-4L,
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3.5087109907378343612154047611394786e-2L};
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#endif
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static const long double c1 = (22713.0L / 32768.0L);
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static const long double c2 = 1.4286068203094172321214581765680755e-6L;
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static const long double hugexp = LHUGE_EXP;
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static const long double invln2 = 1.4426950408889634073599246810018921L;
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_CRTIMP2 short __cdecl _LExp(long double *px, long 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 == 0.0L)
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{ /* certain underflow */
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*px = 0.0L;
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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 = _LInf._Long_double;
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return (_INFCODE);
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}
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else
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{ /* xexp won't overflow */
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long double g = *px * invln2;
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short xexp = (short)(g + (g < 0 ? - 0.5L : + 0.5L));
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g = xexp;
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g = (*px - g * c1) - g * c2;
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if (-_LEps._Long_double < g && g < _LEps._Long_double)
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*px = y;
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else
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{ /* g*g worth computing */
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#if _DLONG <= 1 /* assume IEEE 754 10 byte */
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const long double z = g * g;
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const long double w = ((z + q[1]) * z + q[2]) * z + q[3];
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g *= (p[0] * z + p[1]) * z + p[2];
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*px = (w + g) / (w - g) * 2.0L * y;
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--xexp;
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#else /* assume IEEE 754 16 byte */
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const long double z = g * g;
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const long double w = ((q[0] * z + q[1]) * z + q[2]) * z + q[3];
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const long double v = (((p[0] * z + p[1]) * z + p[2])
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* z + p[3]) * z + p[4];
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const long double u = g * w - v;
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*px = g * (g + z * (w + w + u)) / (2.0L - (g + z * u)) + g + 1.0;
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*px *= y;
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#endif
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}
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return (_LDscale(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) 1992-2001 by P.J. Plauger. ALL RIGHTS RESERVED.
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* Consult your license regarding permissions and restrictions.
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V3.10:0009 */
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