atan2.c   [plain text]


/*
 * Copyright (c) 2002 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*******************************************************************************
*                                                                              *
*     File atan2.c,                                                            *
*     Function atan2(y/x),                                                     *
*     Implementation of arc tangent of ( y / x ) for the PowerPC.              *
*                                                                              *
*     Copyright c 1991-2001 Apple Computer, Inc.  All rights reserved.         *
*                                                                              *
*     Written by Ali Sazegari, started on November 1991,                       *
*     Modified and ported by Robert A. Murley (ram) for Mac OS X.              *
*                                                                              *
*     A MathLib v4 file.                                                       *
*                                                                              *
*     December 03 1992: first rs6000 port.                                     *
*     January  05 1993: added the environmental controls.                      *
*     July     07 1993: fixed the argument of __fpclassifyd.                   *
*     July     11 1993: changed feholdexcept to _feprocentry to set rounding   *
*                       to zero. removed the constant nan, fixed all edge      *
*                       cases to reflect the fpce-nceg requirements.           *
*     September19 1994: changed all the environemntal enquiries to __setflm.   *
*     October  06 1994: initialized CurrentEnvironment to correct an invalid   *
*                        flag problem.                                         *
*     July     23 2001: replaced __setflm with fegetenvd/fesetenvd;            *
*                       replaced DblInHex typedef with hexdouble.              *
*     September 07 2001: added #ifdef __ppc__.                                 *
*     September 09 2001: added more comments.                                  *
*     September 10 2001: added macros to detect PowerPC and correct compiler.  *
*     September 18 2001: added <CoreServices/CoreServices.h> to get to <fp.h>  *
*                        and <fenv.h>.                                         *
*     September 25 2001: removed fenv_access pragma.                           *
*     October   05 2001: added const double pi.                                *
*     October   08 2001: removed <CoreServices/CoreServices.h>.                *
*                        changed compiler errors to warnings.                  *
*     November  06 2001: commented out warning about Intel architectures.      *
*                                                                              *
*     W A R N I N G:                                                           *
*     These routines require a 64-bit double precision IEEE-754 model.         *
*     They are written for PowerPC only and are expecting the compiler         *
*     to generate the correct sequence of multiply-add fused instructions.     *
*                                                                              *
*     These routines are not intended for 32-bit Intel architectures.          *
*                                                                              *
*     A version of gcc higher than 932 is required.                            *
*                                                                              *
*     GCC compiler options:                                                    *
*            optimization level 3 (-O3)                                        *
*            -fschedule-insns -finline-functions -funroll-all-loops            *
*                                                                              *
*******************************************************************************/

#ifdef      __APPLE_CC__
#if         __APPLE_CC__ > 930

#include    "math.h"
#include    "fenv_private.h"
#include    "fp_private.h"

static const double pi = 3.141592653589793116e+00;

/*******************************************************************************
*            Functions needed for the computation.                             *
*******************************************************************************/

/*     the following fp.h functions are used:                                 */
/*     atan, __fpclassifyd, copysign and __signbitd.                          */

/*******************************************************************************
*     This function is odd.  The positive interval is computed and for         *
*     negative values, the sign is reflected in the computation.               *
*******************************************************************************/

double atan2 ( double y, double x )
      {
      register double result;
      hexdouble OldEnvironment, CurrentEnvironment;
      CurrentEnvironment.i.lo = 0;
      

/*******************************************************************************
*     If argument is SNaN then a QNaN has to be returned and the invalid       *
*     flag signaled.                                                           * 
*******************************************************************************/

      if ( ( x != x ) || ( y != y ) )
            return x + y;
      
      fegetenvd( OldEnvironment.d );
      fesetenvd( 0.0 );

/*******************************************************************************
*     The next switch will decipher what sort of argument we have:             *
*                                                                              *
*     atan2 ( 0, x ) = 0, if x > 0,                                          *
*     atan2 ( 0, +0) = 0,                                                    *
*     atan2 ( 0, x ) = , if x < 0,                                          *
*     atan2 ( 0, -0) = ,                                                    *
*     atan2 ( y, 0 ) = /2, if y > 0,                                         *
*     atan2 ( y, 0 ) = -/2, if y < 0,                                        *
*     atan2 ( y,  ) = 0, for finite y > 0,                                  *
*     atan2 ( , x ) = /2, for finite x,                                    *
*     atan2 ( y, -) = , for finite y > 0,                                  *
*     atan2 ( ,  ) = /4,                                                  *
*     atan2 ( , -) = 3/4.                                                 *
*                                                                              *
*     note that the non obvious cases are y and x both infinite or both zero.  *
*     for more information, see Branch Cuts for Complex Elementary Functions, *
*     or much Much Ado About Nothings Sign bit, by W. Kahan, Proceedings of  *
*     the joint IMA/SIAM conference on The state of the Art in Numerical       *
*     Analysis, 14-18 April 1986, Clarendon Press (1987).                      *
*                                                                              *
*     atan2(y,0) does not raise the divide-by-zero exception, nor does         *
*     atan2(0,0) raise the invalid exception.                                  *
*******************************************************************************/

      switch ( __fpclassifyd ( x ) )
            {
            case FP_ZERO:
                  CurrentEnvironment.i.lo |= FE_INEXACT;
                  if ( y > 0.0 )
                        x = + 0.5 * pi;
                  else if ( y < 0.0 )
                        x = - 0.5 * pi;
                  else
                        {
                        if ( __signbitd ( x ) )
                              x = copysign ( pi, y );
                        else
                              {
                              CurrentEnvironment.i.lo &= ~FE_INEXACT;
                              x = y;
                              }
                        }
                  OldEnvironment.i.lo |= CurrentEnvironment.i.lo;
                  fesetenvd( OldEnvironment.d );
                  return x;
            case FP_INFINITE:
                  if ( x > 0.0 )
                        {
                        if ( __isfinited ( y ) )
                              x = copysign ( 0.0, y );
                        else
                              {
                              CurrentEnvironment.i.lo |= FE_INEXACT;
                              x = copysign ( 0.25 * pi, y );
                              }
                        }
                  else
                        {
                        CurrentEnvironment.i.lo |= FE_INEXACT;
                        if ( __isfinited ( y ) )
                              x = copysign ( pi, y );
                        else
                              x = copysign ( 0.75 * pi, y );
                        }
                  OldEnvironment.i.lo |= CurrentEnvironment.i.lo;
                  fesetenvd( OldEnvironment.d );
                  return x;
            default:
                  break;
            }
                        
      switch ( __fpclassifyd ( y ) )
            {
            case FP_ZERO:
                  if ( x > 0.0 )
                        x = y;
                  else
                        {
                        CurrentEnvironment.i.lo |= FE_INEXACT;
                        x = copysign ( pi, y );
                        }
                  OldEnvironment.i.lo |= CurrentEnvironment.i.lo;
                  fesetenvd( OldEnvironment.d );
                  return x;
            case FP_INFINITE:
                  CurrentEnvironment.i.lo |= FE_INEXACT;
                  x = copysign ( 0.5 * pi, y );
                  OldEnvironment.i.lo |= CurrentEnvironment.i.lo;
                  fesetenvd( OldEnvironment.d );
                  return x;
            default:
                  break;
            }
      
/*******************************************************************************
*     End of the special case section. atan2 is mostly a collection of special *
*     case functions.  Next we will carry out the main computation which at    *
*     this point will only receive normal or denormal numbers.                 *
*******************************************************************************/
      
      result = atan ( __fabs ( y / x ) );
      fegetenvd( CurrentEnvironment.d );
      CurrentEnvironment.i.lo &= ~( FE_UNDERFLOW | FE_OVERFLOW );
      if ( __signbitd ( x ) )
            result = pi - result;

      switch ( __fpclassifyd ( result ) )
            {
            case FP_SUBNORMAL:
                  CurrentEnvironment.i.lo |= FE_UNDERFLOW;
                  /* FALL THROUGH */
            case FP_NORMAL:
                  CurrentEnvironment.i.lo |= FE_INEXACT;
                  /* FALL THROUGH */
            default:
                  break;
            }
            
      OldEnvironment.i.lo |= CurrentEnvironment.i.lo;
      fesetenvd( OldEnvironment.d );

      return ( copysign ( result, y ) );
      }

#ifdef notdef
float atan2f( float y, float x)
{
    return (float)atan2( y, x );
}
#endif

#else       /* __APPLE_CC__ version */
#warning A higher version than gcc-932 is required.
#endif      /* __APPLE_CC__ version */
#endif      /* __APPLE_CC__ */