osprey/libm/mips/atanf.c

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/*
 * Copyright 2003, 2004, 2005, 2006 PathScale, Inc.  All Rights Reserved.
 */


/*

  Copyright (C) 2000, 2001 Silicon Graphics, Inc.  All Rights Reserved.

  This program is free software; you can redistribute it and/or modify it
  under the terms of version 2.1 of the GNU Lesser General Public License 
  as published by the Free Software Foundation.

  This program is distributed in the hope that it would be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  

  Further, this software is distributed without any warranty that it is
  free of the rightful claim of any third person regarding infringement 
  or the like.  Any license provided herein, whether implied or 
  otherwise, applies only to this software file.  Patent licenses, if
  any, provided herein do not apply to combinations of this program with 
  other software, or any other product whatsoever.  

  You should have received a copy of the GNU Lesser General Public 
  License along with this program; if not, write the Free Software 
  Foundation, Inc., 59 Temple Place - Suite 330, Boston MA 02111-1307, 
  USA.

  Contact information:  Silicon Graphics, Inc., 1600 Amphitheatre Pky,
  Mountain View, CA 94043, or:

  http://www.sgi.com

  For further information regarding this notice, see:

  http://oss.sgi.com/projects/GenInfo/NoticeExplan

*/

/* ====================================================================
 * ====================================================================
 *
 * Module: atanf.c
 * $Revision: 1.5 $
 * $Date: 04/12/21 14:58:21-08:00 $
 * $Author: bos@eng-25.internal.keyresearch.com $
 * $Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.atanf.c $
 *
 * Revision history:
 *  09-Jun-93 - Original Version
 *
 * Description: source code for atanf function
 *
 * ====================================================================
 * ====================================================================
 */

static char *rcs_id = "$Source: /home/bos/bk/kpro64-pending/libm/mips/SCCS/s.atanf.c $ $Revision: 1.5 $";

#ifdef _CALL_MATHERR
#include <stdio.h>
#include <math.h>
#include <errno.h>
#endif

#include "libm.h"

#if defined(mips) && !defined(__GNUC__)
extern  float fatan(float);
extern  float atanf(float);

#pragma weak fatan = __atanf
#pragma weak atanf = __atanf
#endif

#if defined(BUILD_OS_DARWIN) /* Mach-O doesn't support aliases */
extern float __atanf(float);
#pragma weak atanf
float atanf( float x ) {
  return __atanf( x );
}
#elif defined(__GNUC__)
extern  float  __atanf(float);
float    atanf(float) __attribute__ ((weak, alias ("__atanf")));
#endif

/* coefficients for rational approximation of atan on [-1.0, 1.0]        */

static const du P[] =
{
{D(0x4033b1f1, 0x5145e7e8)},
{D(0x4036468d, 0x2d72b575)},
{D(0x4016a439, 0x0afa7438)},
{D(0x3fc69c34, 0x97688a95)},
};

static const du Q[] =
{
{D(0x4033b1f1, 0x5145e7e8)},
{D(0x403cd732, 0xd729eaa7)},
{D(0x4026ab7d, 0x65d9a7a4)},
{D(0x3ff00000, 0x00000000)},
};

/* coefficients for rational approximation of atan(1/x) for |x| > 1.0    */

static const du P2[] =
{
{D(0x3f825e40, 0xbe79ec0c)},
{D(0x3fd264c4, 0x2019db77)},
{D(0x3ff218ab, 0x3c579116)},
{D(0x3ff00000, 0x00000000)},
};

static const du Q2[] =
{
{D(0x3fa9ff0f, 0x6b64219d)},
{D(0x3fe26aab, 0x734ccc2a)},
{D(0x3ff76e00, 0x7ae4fafe)},
{D(0x3ff00000, 0x00000000)},
};

static const du piby2 =
{D(0x3ff921fb, 0x54442d18)};

static const  fu  Qnan = {QNANF};

static const fu fpiby2 =
{0x3fc90fdb};


/* ====================================================================
 *
 * FunctionName   atanf
 *
 * Description    computes arctangent of arg
 *
 * ====================================================================
 */

float
__atanf( float x )
{
int ix, xpt;
double  dx, xsq, num, denom;
float result;
#ifdef _CALL_MATHERR
struct exception  exstruct;
#endif

  FLT2INT(x, ix);   /* copy arg to an integer */
  xpt = (ix >> MANTWIDTH);
  xpt &= 0xff;

  if ( xpt < 0x7f ) 
  {
    /* |x| < 1.0 */

    dx = x;

    if ( xpt >= 0x73 )
    {
      /* |x| >= 2^(-12) */

      xsq = dx*dx;

      num = ((P[3].d*xsq + P[2].d)*xsq + P[1].d)*xsq + P[0].d;

      denom = ((xsq + Q[2].d)*xsq + Q[1].d)*xsq + Q[0].d;

      result = (x*num)/denom;

      return ( result );
    }

    return (x);
  }

  if ( xpt < 0x98 )
  {
    /* 1.0 <= |x| < 2^24 */

    /* compute atan(|x|) = pi/2 - atan(1/|x|) by rewriting the
       rational approximation to atan(1/|x|)
    */

    dx = fabsf(x);

    xsq = dx*dx;

    num = ((xsq + P2[2].d)*xsq + P2[1].d)*xsq + P2[0].d;

    denom = ((xsq + Q2[2].d)*xsq + Q2[1].d)*xsq + Q2[0].d;

    result = piby2.d - num/(dx*denom);

    if ( x < (float)0.0 )
      result = -result;

    return ( result );
  }

  if ( x != x )
  {
    /* x is a NaN; return a quiet NaN */

#ifdef _CALL_MATHERR

                exstruct.type = DOMAIN;
                exstruct.name = "atanf";
                exstruct.arg1 = x;
                exstruct.retval = Qnan.f;

                if ( matherr( &exstruct ) == 0 )
                {
                        fprintf(stderr, "domain error in atanf\n");
                        SETERRNO(EDOM);
                }

                return ( exstruct.retval );
#else
    NAN_SETERRNO(EDOM);
    
    return ( Qnan.f );
#endif
  }

  result = fpiby2.f;

  if ( x < (float)0.0 )
    result = -result;

  return ( result );

}

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