niceSOFT/mpfr | Gitverse

src/get_si.c
80 строк2 KB
Vincent Lefèvre
03 янв 2018, 13:53
03 янв 2018, 13:532fce388
/* mpfr_get_si -- convert a floating-point number to a signed long.

Copyright 2003-2018 Free Software Foundation, Inc.
Contributed by the AriC and Caramba 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. */

#include "mpfr-impl.h"

long
mpfr_get_si (mpfr_srcptr f, mpfr_rnd_t rnd)
{
  mpfr_prec_t prec;
  long s;
  mpfr_t x;
  MPFR_SAVE_EXPO_DECL (expo);

  if (MPFR_UNLIKELY (!mpfr_fits_slong_p (f, rnd)))
    {
      MPFR_SET_ERANGEFLAG ();
      return MPFR_IS_NAN (f) ? 0 :
        MPFR_IS_NEG (f) ? LONG_MIN : LONG_MAX;
    }

  if (MPFR_IS_ZERO (f))
    return (long) 0;

  /* Determine the precision of long. |LONG_MIN| may have one more bit
     as an integer, but in this case, this is a power of 2, thus fits
     in a precision-prec floating-point number. */
  for (s = LONG_MAX, prec = 0; s != 0; s /= 2, prec++)
    { }

  MPFR_SAVE_EXPO_MARK (expo);

  /* first round to prec bits */
  mpfr_init2 (x, prec);
  mpfr_rint (x, f, rnd);

  /* The flags from mpfr_rint are the wanted ones. In particular,
     it sets the inexact flag when necessary. */
  MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);

  /* warning: if x=0, taking its exponent is illegal */
  if (MPFR_UNLIKELY (MPFR_IS_ZERO(x)))
    s = 0;
  else
    {
      mp_limb_t a;
      mp_size_t n;
      mpfr_exp_t exp;

      /* now the result is in the most significant limb of x */
      exp = MPFR_GET_EXP (x); /* since |x| >= 1, exp >= 1 */
      n = MPFR_LIMB_SIZE(x);
      a = MPFR_MANT(x)[n - 1] >> (GMP_NUMB_BITS - exp);
      s = MPFR_IS_POS (f) ? a : a <= LONG_MAX ? - (long) a : LONG_MIN;
    }

  mpfr_clear (x);

  MPFR_SAVE_EXPO_FREE (expo);

  return s;
}