/****************************************************************************
 * libs/libm/libm/lib_sin.c
 *
 * SPDX-License-Identifier: ISC
 * SPDX-FileCopyrightText: Copyright (C) 2012 Gregory Nutt.
 * SPDX-FileContributor: Ported by: Darcy Gong
 *
 * It derives from the Rhombus OS math library by Nick Johnson which has
 * a compatible, MIT-style license:
 *
 * Copyright (C) 2009-2011 Nick Johnson <nickbjohnson4224 at gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <sys/types.h>
#include <math.h>

/****************************************************************************
 * Private Data
 ****************************************************************************/

static double _dbl_inv_fact[] =
{
  1.0 / 1.0,                    /* 1 / 1! */
  1.0 / 6.0,                    /* 1 / 3! */
  1.0 / 120.0,                  /* 1 / 5! */
  1.0 / 5040.0,                 /* 1 / 7! */
  1.0 / 362880.0,               /* 1 / 9! */
  1.0 / 39916800.0,             /* 1 / 11! */
  1.0 / 6227020800.0,           /* 1 / 13! */
  1.0 / 1307674368000.0,        /* 1 / 15! */
  1.0 / 355687428096000.0,      /* 1 / 17! */
  1.0 / 121645100408832000.0,   /* 1 / 19! */
};

/****************************************************************************
 * Public Functions
 ****************************************************************************/

double sin(double x)
{
  double x_squared;
  double sin_x;
  size_t i;

  /* Move x to [-pi, pi) */

  x = fmod(x, 2 * M_PI);
  if (x >= M_PI)
    {
      x -= 2 * M_PI;
    }

  if (x < -M_PI)
    {
      x += 2 * M_PI;
    }

  /* Move x to [-pi/2, pi/2) */

  if (x >= M_PI_2)
    {
      x = M_PI - x;
    }

  if (x < -M_PI_2)
    {
      x = -M_PI - x;
    }

  x_squared = x * x;
  sin_x = 0.0;

  /* Perform Taylor series approximation for sin(x) with ten terms */

  for (i = 0; i < 10; i++)
    {
      if (i % 2 == 0)
        {
          sin_x += x * _dbl_inv_fact[i];
        }
      else
        {
          sin_x -= x * _dbl_inv_fact[i];
        }

      x *= x_squared;
    }

  return sin_x;
}
