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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.18.0/] [newlib/] [libm/] [mathfp/] [sf_exp.c] - Rev 214
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/* @(#)z_expf.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. ******************************************************************/ /****************************************************************** * 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" static const float INV_LN2 = 1.442695040; static const float LN2 = 0.693147180; static const float p[] = { 0.249999999950, 0.00416028863 }; static const float q[] = { 0.5, 0.04998717878 }; float _DEFUN (expf, (float), float x) { int N; float g, z, R, P, Q; switch (numtestf (x)) { case NAN: errno = EDOM; return (x); case INF: errno = ERANGE; if (isposf (x)) return (z_infinity_f.f); 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_f < x && x < z_rooteps_f) { 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[1] * z + p[0]); Q = q[1] * z + q[0]; R = 0.5 + P / (Q - P); /* Return the floating point value. */ N++; return (ldexpf (R, N)); } #ifdef _DOUBLE_IS_32BITS double exp (double x) { return (double) expf ((float) x); } #endif /* _DOUBLE_IS_32BITS */
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