xref: /dflybsd-src/contrib/mpfr/src/sin.c (revision 2786097444a0124b5d33763854de247e230c6629)

/* mpfr_sin -- sine of a floating-point number

Copyright 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
Contributed by the AriC and Caramel projects, INRIA.

This file is part of the GNU MPFR Library.

The GNU MPFR 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 3 of the License, or (at your
option) any later version.

The GNU MPFR 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 MPFR Library; see the file COPYING.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"

static int
mpfr_sin_fast (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
{
  int inex;

  inex = mpfr_sincos_fast (y, NULL, x, rnd_mode);
  inex = inex & 3; /* 0: exact, 1: rounded up, 2: rounded down */
  return (inex == 2) ? -1 : inex;
}

int
mpfr_sin (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
{
  mpfr_t c, xr;
  mpfr_srcptr xx;
  mpfr_exp_t expx, err;
  mpfr_prec_t precy, m;
  int inexact, sign, reduce;
  MPFR_ZIV_DECL (loop);
  MPFR_SAVE_EXPO_DECL (expo);

  MPFR_LOG_FUNC
    (("x[%Pu]=%.*Rg rnd=%d", mpfr_get_prec (x), mpfr_log_prec, x, rnd_mode),
     ("y[%Pu]=%.*Rg inexact=%d", mpfr_get_prec (y), mpfr_log_prec, y,
      inexact));

  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
    {
      if (MPFR_IS_NAN (x) || MPFR_IS_INF (x))
        {
          MPFR_SET_NAN (y);
          MPFR_RET_NAN;

        }
      else /* x is zero */
        {
          MPFR_ASSERTD (MPFR_IS_ZERO (x));
          MPFR_SET_ZERO (y);
          MPFR_SET_SAME_SIGN (y, x);
          MPFR_RET (0);
        }
    }

  /* sin(x) = x - x^3/6 + ... so the error is < 2^(3*EXP(x)-2) */
  MPFR_FAST_COMPUTE_IF_SMALL_INPUT (y, x, -2 * MPFR_GET_EXP (x), 2, 0,
                                    rnd_mode, {});

  MPFR_SAVE_EXPO_MARK (expo);

  /* Compute initial precision */
  precy = MPFR_PREC (y);

  if (precy >= MPFR_SINCOS_THRESHOLD)
    return mpfr_sin_fast (y, x, rnd_mode);

  m = precy + MPFR_INT_CEIL_LOG2 (precy) + 13;
  expx = MPFR_GET_EXP (x);

  mpfr_init (c);
  mpfr_init (xr);

  MPFR_ZIV_INIT (loop, m);
  for (;;)
    {
      /* first perform argument reduction modulo 2*Pi (if needed),
         also helps to determine the sign of sin(x) */
      if (expx >= 2) /* If Pi < x < 4, we need to reduce too, to determine
                        the sign of sin(x). For 2 <= |x| < Pi, we could avoid
                        the reduction. */
        {
          reduce = 1;
          /* As expx + m - 1 will silently be converted into mpfr_prec_t
             in the mpfr_set_prec call, the assert below may be useful to
             avoid undefined behavior. */
          MPFR_ASSERTN (expx + m - 1 <= MPFR_PREC_MAX);
          mpfr_set_prec (c, expx + m - 1);
          mpfr_set_prec (xr, m);
          mpfr_const_pi (c, MPFR_RNDN);
          mpfr_mul_2ui (c, c, 1, MPFR_RNDN);
          mpfr_remainder (xr, x, c, MPFR_RNDN);
          /* The analysis is similar to that of cos.c:
             |xr - x - 2kPi| <= 2^(2-m). Thus we can decide the sign
             of sin(x) if xr is at distance at least 2^(2-m) of both
             0 and +/-Pi. */
          mpfr_div_2ui (c, c, 1, MPFR_RNDN);
          /* Since c approximates Pi with an error <= 2^(2-expx-m) <= 2^(-m),
             it suffices to check that c - |xr| >= 2^(2-m). */
          if (MPFR_SIGN (xr) > 0)
            mpfr_sub (c, c, xr, MPFR_RNDZ);
          else
            mpfr_add (c, c, xr, MPFR_RNDZ);
          if (MPFR_IS_ZERO(xr)
              || MPFR_GET_EXP(xr) < (mpfr_exp_t) 3 - (mpfr_exp_t) m
              || MPFR_IS_ZERO(c)
              || MPFR_GET_EXP(c) < (mpfr_exp_t) 3 - (mpfr_exp_t) m)
            goto ziv_next;

          /* |xr - x - 2kPi| <= 2^(2-m), thus |sin(xr) - sin(x)| <= 2^(2-m) */
          xx = xr;
        }
      else /* the input argument is already reduced */
        {
          reduce = 0;
          xx = x;
        }

      sign = MPFR_SIGN(xx);
      /* now that the argument is reduced, precision m is enough */
      mpfr_set_prec (c, m);
      mpfr_cos (c, xx, MPFR_RNDZ);    /* can't be exact */
      mpfr_nexttoinf (c);           /* now c = cos(x) rounded away */
      mpfr_mul (c, c, c, MPFR_RNDU); /* away */
      mpfr_ui_sub (c, 1, c, MPFR_RNDZ);
      mpfr_sqrt (c, c, MPFR_RNDZ);
      if (MPFR_IS_NEG_SIGN(sign))
        MPFR_CHANGE_SIGN(c);

      /* Warning: c may be 0! */
      if (MPFR_UNLIKELY (MPFR_IS_ZERO (c)))
        {
          /* Huge cancellation: increase prec a lot! */
          m = MAX (m, MPFR_PREC (x));
          m = 2 * m;
        }
      else
        {
          /* the absolute error on c is at most 2^(3-m-EXP(c)),
             plus 2^(2-m) if there was an argument reduction.
             Since EXP(c) <= 1, 3-m-EXP(c) >= 2-m, thus the error
             is at most 2^(3-m-EXP(c)) in case of argument reduction. */
          err = 2 * MPFR_GET_EXP (c) + (mpfr_exp_t) m - 3 - (reduce != 0);
          if (MPFR_CAN_ROUND (c, err, precy, rnd_mode))
            break;

          /* check for huge cancellation (Near 0) */
          if (err < (mpfr_exp_t) MPFR_PREC (y))
            m += MPFR_PREC (y) - err;
          /* Check if near 1 */
          if (MPFR_GET_EXP (c) == 1)
            m += m;
        }

    ziv_next:
      /* Else generic increase */
      MPFR_ZIV_NEXT (loop, m);
    }
  MPFR_ZIV_FREE (loop);

  inexact = mpfr_set (y, c, rnd_mode);
  /* inexact cannot be 0, since this would mean that c was representable
     within the target precision, but in that case mpfr_can_round will fail */

  mpfr_clear (c);
  mpfr_clear (xr);

  MPFR_SAVE_EXPO_FREE (expo);
  return mpfr_check_range (y, inexact, rnd_mode);
}