sysdeps/generic/asin.c

   1 /* Copyright (C) 1991 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <errno.h>
  21 #include <math.h>
  22
  23 /* Return the inverse sine of X.  */
  24 double
  25 DEFUN(asin, (x), double x)
  26 {
  27   double abs_x;
  28
  29   if (__isnan(x))
  30     {
  31       errno = EDOM;
  32       return x;
  33     }
  34
  35   abs_x = fabs(x);
  36
  37   if (abs_x <= 0.5)
  38     return atan2(x, sqrt(1.0 - (x * x)));
  39   else
  40     {
  41       double t = 1.0 - abs_x;
  42       return atan2(x, sqrt((t + t) - (t * t)));
  43     }
  44 }