source/libs/mpfr/mpfr-3.1.3/src/get_si.c

   1 /* mpfr_get_si -- convert a floating-point number to a signed long.
   2
   3 Copyright 2003-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 long
  26 mpfr_get_si (mpfr_srcptr f, mpfr_rnd_t rnd)
  27 {
  28   mpfr_prec_t prec;
  29   long s;
  30   mpfr_t x;
  31
  32   if (MPFR_UNLIKELY (!mpfr_fits_slong_p (f, rnd)))
  33     {
  34       MPFR_SET_ERANGE ();
  35       return MPFR_IS_NAN (f) ? 0 :
  36         MPFR_IS_NEG (f) ? LONG_MIN : LONG_MAX;
  37     }
  38
  39   if (MPFR_IS_ZERO (f))
  40     return (long) 0;
  41
  42   /* determine prec of long */
  43   for (s = LONG_MIN, prec = 0; s != 0; s /= 2, prec++)
  44     { }
  45
  46   /* first round to prec bits */
  47   mpfr_init2 (x, prec);
  48   mpfr_rint (x, f, rnd);
  49
  50   /* warning: if x=0, taking its exponent is illegal */
  51   if (MPFR_UNLIKELY (MPFR_IS_ZERO(x)))
  52     s = 0;
  53   else
  54     {
  55       mp_limb_t a;
  56       mp_size_t n;
  57       mpfr_exp_t exp;
  58
  59       /* now the result is in the most significant limb of x */
  60       exp = MPFR_GET_EXP (x); /* since |x| >= 1, exp >= 1 */
  61       n = MPFR_LIMB_SIZE(x);
  62       a = MPFR_MANT(x)[n - 1] >> (GMP_NUMB_BITS - exp);
  63       s = MPFR_SIGN(f) > 0 ? a : a <= LONG_MAX ? - (long) a : LONG_MIN;
  64     }
  65
  66   mpfr_clear (x);
  67
  68   return s;
  69 }