sysdeps/ieee754/dbl-64/x2y2m1f.c

   1 /* Compute x^2 + y^2 - 1, without large cancellation error.
   2    Copyright (C) 2012-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <math.h>
  20 #include <math_private.h>
  21 #include <float.h>
  22
  23 /* Return X^2 + Y^2 - 1, computed without large cancellation error.
  24    It is given that 1 > X >= Y >= epsilon / 2, and that X^2 + Y^2 >=
  25    0.5.  */
  26
  27 float
  28 __x2y2m1f (float x, float y)
  29 {
  30   double dx = x, dy = y;
  31   return (float) ((dx - 1) * (dx + 1) + dy * dy);
  32 }