source/libs/mpfr/mpfr-src/src/get_z.c

   1 /* mpfr_get_z -- get a multiple-precision integer from
   2                  a floating-point number
   3
   4 Copyright 2004, 2006-2016 Free Software Foundation, Inc.
   5 Contributed by the AriC and Caramba projects, INRIA.
   6
   7 This file is part of the GNU MPFR Library.
   8
   9 The GNU MPFR Library is free software; you can redistribute it and/or modify
  10 it under the terms of the GNU Lesser General Public License as published by
  11 the Free Software Foundation; either version 3 of the License, or (at your
  12 option) any later version.
  13
  14 The GNU MPFR Library is distributed in the hope that it will be useful, but
  15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  17 License for more details.
  18
  19 You should have received a copy of the GNU Lesser General Public License
  20 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  21 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  22 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  23
  24 #include "mpfr-impl.h"
  25
  26 int
  27 mpfr_get_z (mpz_ptr z, mpfr_srcptr f, mpfr_rnd_t rnd)
  28 {
  29   int inex;
  30   mpfr_t r;
  31   mpfr_exp_t exp;
  32
  33   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
  34     {
  35       if (MPFR_UNLIKELY (MPFR_NOTZERO (f)))
  36         MPFR_SET_ERANGE ();
  37       mpz_set_ui (z, 0);
  38       /* The ternary value is 0 even for infinity. Giving the rounding
  39          direction in this case would not make much sense anyway, and
  40          the direction would not necessarily match rnd. */
  41       return 0;
  42     }
  43
  44   exp = MPFR_GET_EXP (f);
  45   /* if exp <= 0, then |f|<1, thus |o(f)|<=1 */
  46   MPFR_ASSERTN (exp < 0 || exp <= MPFR_PREC_MAX);
  47   mpfr_init2 (r, (exp < (mpfr_exp_t) MPFR_PREC_MIN ?
  48                   MPFR_PREC_MIN : (mpfr_prec_t) exp));
  49   inex = mpfr_rint (r, f, rnd);
  50   MPFR_ASSERTN (inex != 1 && inex != -1); /* integral part of f is
  51                                              representable in r */
  52   MPFR_ASSERTN (MPFR_IS_FP (r));
  53   exp = mpfr_get_z_2exp (z, r);
  54   if (exp >= 0)
  55     mpz_mul_2exp (z, z, exp);
  56   else
  57     mpz_fdiv_q_2exp (z, z, -exp);
  58   mpfr_clear (r);
  59
  60   return inex;
  61 }