glibc/sysdeps/ieee754/flt-32/s_cosf.c

/* Compute cosine of argument.
   Copyright (C) 2018 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
   <http://www.gnu.org/licenses/>.  */

#include <stdint.h>
#include <math.h>
#include <math-barriers.h>
#include <libm-alias-float.h>
#include "math_config.h"
#include "s_sincosf.h"

#ifndef COSF
# define COSF_FUNC __cosf
#else
# define COSF_FUNC COSF
#endif

/* Fast cosf implementation.  Worst-case ULP is 0.5607, maximum relative
   error is 0.5303 * 2^-23.  A single-step range reduction is used for
   small values.  Large inputs have their range reduced using fast integer
   arithmetic.
*/
float
COSF_FUNC (float y)
{
  double x = y;
  double s;
  int n;
  const sincos_t *p = &__sincosf_table[0];

  if (abstop12 (y) < abstop12 (pio4))
    {
      double x2 = x * x;

      if (__glibc_unlikely (abstop12 (y) < abstop12 (0x1p-12f)))
	return 1.0f;

      return sinf_poly (x, x2, p, 1);
    }
  else if (__glibc_likely (abstop12 (y) < abstop12 (120.0f)))
    {
      x = reduce_fast (x, p, &n);

      /* Setup the signs for sin and cos.  */
      s = p->sign[n & 3];

      if (n & 2)
	p = &__sincosf_table[1];

      return sinf_poly (x * s, x * x, p, n ^ 1);
    }
  else if (abstop12 (y) < abstop12 (INFINITY))
    {
      uint32_t xi = asuint (y);
      int sign = xi >> 31;

      x = reduce_large (xi, &n);

      /* Setup signs for sin and cos - include original sign.  */
      s = p->sign[(n + sign) & 3];

      if ((n + sign) & 2)
	p = &__sincosf_table[1];

      return sinf_poly (x * s, x * x, p, n ^ 1);
    }
  else
    return __math_invalidf (y);
}

#ifndef COSF
libm_alias_float (__cos, cos)
#endif