source/libs/mpfr/mpfr-3.1.3/src/div_2ui.c

   1 /* mpfr_div_2ui -- divide a floating-point number by a power of two
   2
   3 Copyright 1999, 2001-2015 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 int
  26 mpfr_div_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long n, mpfr_rnd_t rnd_mode)
  27 {
  28   int inexact;
  29
  30   MPFR_LOG_FUNC (
  31     ("x[%Pu]=%.*Rg n=%lu rnd=%d", mpfr_get_prec(x), mpfr_log_prec, x, n,
  32      rnd_mode),
  33     ("y[%Pu]=%.*Rg inexact=%d", mpfr_get_prec(y), mpfr_log_prec, y, inexact));
  34
  35   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
  36     return mpfr_set (y, x, rnd_mode);
  37   else
  38     {
  39       mpfr_exp_t exp = MPFR_GET_EXP (x);
  40       mpfr_uexp_t diffexp;
  41
  42       MPFR_SETRAW (inexact, y, x, exp, rnd_mode);
  43       diffexp = (mpfr_uexp_t) exp - (mpfr_uexp_t) (__gmpfr_emin - 1);
  44       if (MPFR_UNLIKELY (n >= diffexp))  /* exp - n <= emin - 1 */
  45         {
  46           if (rnd_mode == MPFR_RNDN &&
  47               (n > diffexp || (inexact >= 0 && mpfr_powerof2_raw (y))))
  48             rnd_mode = MPFR_RNDZ;
  49           return mpfr_underflow (y, rnd_mode, MPFR_SIGN (y));
  50         }
  51       /* exp - n >= emin (no underflow, no integer overflow) */
  52       while (n > LONG_MAX)
  53         {
  54           n -= LONG_MAX;
  55           exp -= LONG_MAX;  /* note: signed values */
  56         }
  57       MPFR_SET_EXP (y, exp - (long) n);
  58     }
  59
  60   MPFR_RET (inexact);
  61 }