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[/] [openrisc/] [trunk/] [gnu-stable/] [newlib-1.18.0/] [newlib/] [libm/] [mathfp/] [sf_logarithm.c] - Rev 859
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/* @(#)z_logarithmf.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. ******************************************************************/ /****************************************************************** * Logarithm * * Input: * x - floating point value * ten - indicates base ten numbers * * Output: * logarithm of x * * Description: * This routine calculates logarithms. * *****************************************************************/ #include "fdlibm.h" #include "zmath.h" static const float a[] = { -0.5527074855 }; static const float b[] = { -0.6632718214e+1 }; static const float C1 = 0.693145752; static const float C2 = 1.428606820e-06; static const float C3 = 0.4342944819; float _DEFUN (logarithmf, (float, int), float x _AND int ten) { int N; float f, w, z; /* Check for domain/range errors here. */ if (x == 0.0) { errno = ERANGE; return (-z_infinity_f.f); } else if (x < 0.0) { errno = EDOM; return (z_notanum_f.f); } else if (!isfinitef(x)) { if (isnanf(x)) return (z_notanum_f.f); else return (z_infinity_f.f); } /* Get the exponent and mantissa where x = f * 2^N. */ f = frexpf (x, &N); z = f - 0.5; if (f > __SQRT_HALF) z = (z - 0.5) / (f * 0.5 + 0.5); else { N--; z /= (z * 0.5 + 0.5); } w = z * z; /* Use Newton's method with 4 terms. */ z += z * w * (a[0]) / ((w + 1.0) * w + b[0]); if (N != 0) z = (N * C2 + z) + N * C1; if (ten) z *= C3; return (z); }
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