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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.18.0/] [newlib/] [libm/] [mathfp/] [s_exp.c] - Rev 207
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/* @(#)z_exp.c 1.0 98/08/13 */ /****************************************************************** * The following routines are coded directly from the algorithms * and coefficients given in "Software Manual for the Elementary * Functions" by William J. Cody, Jr. and William Waite, Prentice * Hall, 1980. ******************************************************************/ /* FUNCTION <<exp>>, <<expf>>---exponential INDEX exp INDEX expf ANSI_SYNOPSIS #include <math.h> double exp(double <[x]>); float expf(float <[x]>); TRAD_SYNOPSIS #include <math.h> double exp(<[x]>); double <[x]>; float expf(<[x]>); float <[x]>; DESCRIPTION <<exp>> and <<expf>> calculate the exponential of <[x]>, that is, @ifnottex e raised to the power <[x]> (where e @end ifnottex @tex $e^x$ (where $e$ @end tex is the base of the natural system of logarithms, approximately 2.71828). RETURNS On success, <<exp>> and <<expf>> return the calculated value. If the result underflows, the returned value is <<0>>. If the result overflows, the returned value is <<HUGE_VAL>>. In either case, <<errno>> is set to <<ERANGE>>. PORTABILITY <<exp>> is ANSI C. <<expf>> is an extension. */ /***************************************************************** * Exponential Function * * Input: * x - floating point value * * Output: * e raised to x. * * Description: * This routine returns e raised to the xth power. * *****************************************************************/ #include <float.h> #include "fdlibm.h" #include "zmath.h" #ifndef _DOUBLE_IS_32BITS static const double INV_LN2 = 1.4426950408889634074; static const double LN2 = 0.6931471805599453094172321; static const double p[] = { 0.25, 0.75753180159422776666e-2, 0.31555192765684646356e-4 }; static const double q[] = { 0.5, 0.56817302698551221787e-1, 0.63121894374398504557e-3, 0.75104028399870046114e-6 }; double _DEFUN (exp, (double), double x) { int N; double g, z, R, P, Q; switch (numtest (x)) { case NAN: errno = EDOM; return (x); case INF: errno = ERANGE; if (ispos (x)) return (z_infinity.d); else return (0.0); case 0: return (1.0); } /* Check for out of bounds. */ if (x > BIGX || x < SMALLX) { errno = ERANGE; return (x); } /* Check for a value too small to calculate. */ if (-z_rooteps < x && x < z_rooteps) { return (1.0); } /* Calculate the exponent. */ if (x < 0.0) N = (int) (x * INV_LN2 - 0.5); else N = (int) (x * INV_LN2 + 0.5); /* Construct the mantissa. */ g = x - N * LN2; z = g * g; P = g * ((p[2] * z + p[1]) * z + p[0]); Q = ((q[3] * z + q[2]) * z + q[1]) * z + q[0]; R = 0.5 + P / (Q - P); /* Return the floating point value. */ N++; return (ldexp (R, N)); } #endif /* _DOUBLE_IS_32BITS */