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[/] [or1k/] [trunk/] [newlib-1.10.0/] [newlib/] [libm/] [mathfp/] [s_tan.c] - Blame information for rev 1765

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1 1010 ivang
 
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/* @(#)z_tan.c 1.0 98/08/13 */
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/******************************************************************
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 * The following routines are coded directly from the algorithms
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 * and coefficients given in "Software Manual for the Elementary
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 * Functions" by William J. Cody, Jr. and William Waite, Prentice
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 * Hall, 1980.
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 ******************************************************************/
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/*
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FUNCTION
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        <<tan>>, <<tanf>>---tangent
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INDEX
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tan
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INDEX
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tanf
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ANSI_SYNOPSIS
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        #include <math.h>
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        double tan(double <[x]>);
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        float tanf(float <[x]>);
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TRAD_SYNOPSIS
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        #include <math.h>
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        double tan(<[x]>)
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        double <[x]>;
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        float tanf(<[x]>)
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        float <[x]>;
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DESCRIPTION
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<<tan>> computes the tangent of the argument <[x]>.
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Angles are specified in radians.
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<<tanf>> is identical, save that it takes and returns <<float>> values.
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RETURNS
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The tangent of <[x]> is returned.
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PORTABILITY
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<<tan>> is ANSI. <<tanf>> is an extension.
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*/
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/******************************************************************
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 * Tangent
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 *
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 * Input:
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 *   x - floating point value
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 *
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 * Output:
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 *   tangent of x
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 *
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 * Description:
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 *   This routine calculates the tangent of x.
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 *
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 *****************************************************************/
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#include "fdlibm.h"
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#include "zmath.h"
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#ifndef _DOUBLE_IS_32BITS
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static const double TWO_OVER_PI = 0.63661977236758134308;
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static const double p[] = { -0.13338350006421960681,
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                             0.34248878235890589960e-2,
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                            -0.17861707342254426711e-4 };
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static const double q[] = { -0.46671683339755294240,
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                             0.25663832289440112864e-1,
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                            -0.31181531907010027307e-3,
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                             0.49819433993786512270e-6 };
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double
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_DEFUN (tan, (double),
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        double x)
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{
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  double y, f, g, XN, xnum, xden, res;
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  int N;
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  /* Check for special values. */
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  switch (numtest (x))
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    {
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      case NAN:
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        errno = EDOM;
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        return (x);
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      case INF:
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        errno = EDOM;
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        return (z_notanum.d);
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    }
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  y = fabs (x);
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  /* Check for values that are out of our range. */
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  if (y > 105414357.0)
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    {
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      errno = ERANGE;
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      return (y);
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    }
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  if (x < 0.0)
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    N = (int) (x * TWO_OVER_PI - 0.5);
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  else
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    N = (int) (x * TWO_OVER_PI + 0.5);
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  XN = (double) N;
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  f = x - N * __PI_OVER_TWO;
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  /* Check for values that are too small. */
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  if (-z_rooteps < f && f < z_rooteps)
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    {
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      xnum = f;
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      xden = 1.0;
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    }
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  /* Calculate the polynomial. */
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  else
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    {
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      g = f * f;
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      xnum = f * ((p[2] * g + p[1]) * g + p[0]) * g + f;
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      xden = (((q[3] * g + q[2]) * g + q[1]) * g + q[0]) * g + 1.0;
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    }
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  if (N & 1)
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    {
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      xnum = -xnum;
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      res = xden / xnum;
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    }
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  else
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    {
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      res = xnum / xden;
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    }
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  return (res);
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}
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#endif /* _DOUBLE_IS_32BITS */

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