math/s_cproj.c

   1 /* Compute projection of complex double value to Riemann sphere.
   2    Copyright (C) 1997, 1999 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <complex.h>
  22 #include <math.h>
  23
  24
  25 __complex__ double
  26 __cproj (__complex__ double x)
  27 {
  28   __complex__ double res;
  29
  30   if (isnan (__real__ x) && isnan (__imag__ x))
  31     return x;
  32   else if (!isfinite (__real__ x) || !isfinite (__imag__ x))
  33     {
  34       __real__ res = INFINITY;
  35       __imag__ res = __copysign (0.0, __imag__ x);
  36     }
  37   else
  38     {
  39       double den = __real__ x * __real__ x + __imag__ x * __imag__ x + 1.0;
  40
  41       __real__ res = (2.0 * __real__ x) / den;
  42       __imag__ res = (2.0 * __imag__ x) / den;
  43     }
  44
  45   return res;
  46 }
  47 weak_alias (__cproj, cproj)
  48 #ifdef NO_LONG_DOUBLE
  49 strong_alias (__cproj, __cprojl)
  50 weak_alias (__cproj, cprojl)
  51 #endif