niceSOFT/mpfr | Gitverse

src/set_ui_2exp.c
72 строки2 KB
Vincent Lefèvre
03 янв 2018, 13:53
03 янв 2018, 13:532fce388
/* mpfr_set_ui_2exp -- set a MPFR number from a machine unsigned integer with
   a shift

Copyright 2004, 2006-2018 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. */

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

MPFR_HOT_FUNCTION_ATTR int
mpfr_set_ui_2exp (mpfr_ptr x, unsigned long i, mpfr_exp_t e, mpfr_rnd_t rnd_mode)
{
  MPFR_SET_POS (x);

  if (MPFR_UNLIKELY (i == 0))
    {
      MPFR_SET_ZERO (x);
      MPFR_RET (0);
    }
  else
    {
      mp_size_t xn;
      int cnt, nbits;
      mp_limb_t *xp;
      int inex = 0;

      /* FIXME: support int limbs (e.g. 16-bit limbs on 16-bit proc) */
      MPFR_ASSERTD (i == (mp_limb_t) i);

      /* Position of the highest limb */
      xn = (MPFR_PREC (x) - 1) / GMP_NUMB_BITS;
      count_leading_zeros (cnt, (mp_limb_t) i);
      MPFR_ASSERTD (cnt < GMP_NUMB_BITS);  /* OK since i != 0 */

      xp = MPFR_MANT(x);
      xp[xn] = ((mp_limb_t) i) << cnt;
      /* Zero the xn lower limbs. */
      MPN_ZERO(xp, xn);

      nbits = GMP_NUMB_BITS - cnt;
      e += nbits;  /* exponent _before_ the rounding */

      /* round if MPFR_PREC(x) smaller than length of i */
      if (MPFR_UNLIKELY (MPFR_PREC (x) < nbits) &&
          MPFR_UNLIKELY (mpfr_round_raw (xp + xn, xp + xn, nbits, 0,
                                         MPFR_PREC (x), rnd_mode, &inex)))
        {
          e++;
          xp[xn] = MPFR_LIMB_HIGHBIT;
        }

      MPFR_EXP (x) = e;
      return mpfr_check_range (x, inex, rnd_mode);
    }
}