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[/] [openrisc/] [trunk/] [gnu-old/] [newlib-1.17.0/] [newlib/] [libm/] [mathfp/] [s_atangent.c] - Rev 822
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/* @(#)z_atangent.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 <<atan>>, <<atanf>>, <<atan2>>, <<atan2f>>, <<atangent>>, <<atangentf>>---arc tangent INDEX atan2 INDEX atan2f INDEX atan INDEX atanf ANSI_SYNOPSIS #include <math.h> double atan(double <[x]>); float atan(float <[x]>); double atan2(double <[y]>,double <[x]>); float atan2f(float <[y]>,float <[x]>); TRAD_SYNOPSIS #include <math.h> double atan2(<[y]>,<[x]>); double <[y]>; double <[x]>; float atan2f(<[y]>,<[x]>); float <[y]>; float <[x]>; #include <math.h> double atan(<[x]>); double <[x]>; float atanf(<[x]>); float <[x]>; DESCRIPTION <<atan2>> computes the inverse tangent (arc tangent) of y / x. <<atan2f>> is identical to <<atan2>>, save that it operates on <<floats>>. <<atan>> computes the inverse tangent (arc tangent) of the input value. <<atanf>> is identical to <<atan>>, save that it operates on <<floats>>. RETURNS @ifnottex <<atan>> returns a value in radians, in the range of -pi/2 to pi/2. <<atan2>> returns a value in radians, in the range of -pi/2 to pi/2. @end ifnottex @tex <<atan>> returns a value in radians, in the range of $-\pi/2$ to $\pi/2$. <<atan2>> returns a value in radians, in the range of $-\pi/2$ to $\pi/2$. @end tex PORTABILITY <<atan>> is ANSI C. <<atanf>> is an extension. <<atan2>> is ANSI C. <<atan2f>> is an extension. */ /****************************************************************** * Arctangent * * Input: * x - floating point value * * Output: * arctangent of x * * Description: * This routine calculates arctangents. * *****************************************************************/ #include <float.h> #include "fdlibm.h" #include "zmath.h" #ifndef _DOUBLE_IS_32BITS static const double ROOT3 = 1.73205080756887729353; static const double a[] = { 0.0, 0.52359877559829887308, 1.57079632679489661923, 1.04719755119659774615 }; static const double q[] = { 0.41066306682575781263e+2, 0.86157349597130242515e+2, 0.59578436142597344465e+2, 0.15024001160028576121e+2 }; static const double p[] = { -0.13688768894191926929e+2, -0.20505855195861651981e+2, -0.84946240351320683534e+1, -0.83758299368150059274 }; double _DEFUN (atangent, (double, double, double, int), double x _AND double v _AND double u _AND int arctan2) { double f, g, R, P, Q, A, res; int N; int branch = 0; int expv, expu; /* Preparation for calculating arctan2. */ if (arctan2) { if (u == 0.0) if (v == 0.0) { errno = ERANGE; return (z_notanum.d); } else { branch = 1; res = __PI_OVER_TWO; } if (!branch) { int e; /* Get the exponent values of the inputs. */ g = frexp (v, &expv); g = frexp (u, &expu); /* See if a divide will overflow. */ e = expv - expu; if (e > DBL_MAX_EXP) { branch = 1; res = __PI_OVER_TWO; } /* Also check for underflow. */ else if (e < DBL_MIN_EXP) { branch = 2; res = 0.0; } } } if (!branch) { if (arctan2) f = fabs (v / u); else f = fabs (x); if (f > 1.0) { f = 1.0 / f; N = 2; } else N = 0; if (f > (2.0 - ROOT3)) { A = ROOT3 - 1.0; f = (((A * f - 0.5) - 0.5) + f) / (ROOT3 + f); N++; } /* Check for values that are too small. */ if (-z_rooteps < f && f < z_rooteps) res = f; /* Calculate the Taylor series. */ else { g = f * f; P = (((p[3] * g + p[2]) * g + p[1]) * g + p[0]) * g; Q = (((g + q[3]) * g + q[2]) * g + q[1]) * g + q[0]; R = P / Q; res = f + f * R; } if (N > 1) res = -res; res += a[N]; } if (arctan2) { if (u < 0.0) res = __PI - res; if (v < 0.0) res = -res; } else if (x < 0.0) { res = -res; } return (res); } #endif /* _DOUBLE_IS_32BITS */
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