/* Return cosine of pi * X.
   Copyright (C) 2024-2025 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <math.h>

FLOAT
M_DECL_FUNC (__cospi) (FLOAT x)
{
  if (isless (M_FABS (x), M_EPSILON))
    return M_LIT (1.0);
  if (__glibc_unlikely (isinf (x)))
    __set_errno (EDOM);
  x = M_FABS (x - M_LIT (2.0) * M_SUF (round) (M_LIT (0.5) * x));
  if (islessequal (x, M_LIT (0.25)))
    return M_SUF (__cos) (M_MLIT (M_PI) * x);
  else if (x == M_LIT (0.5))
    return M_LIT (0.0);
  else if (islessequal (x, M_LIT (0.75)))
    return M_SUF (__sin) (M_MLIT (M_PI) * (M_LIT (0.5) - x));
  else
    return -M_SUF (__cos) (M_MLIT (M_PI) * (M_LIT (1.0) - x));
}
declare_mgen_alias (__cospi, cospi);