contrib/mpfr/src/set_si_2exp.c

   1 /* mpfr_set_si_2exp -- set a MPFR number from a machine signed integer with
   2    a shift
   3
   4 Copyright 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
   5 Contributed by the AriC and Caramel 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 #define MPFR_NEED_LONGLONG_H
  25 #include "mpfr-impl.h"
  26
  27 int
  28 mpfr_set_si_2exp (mpfr_ptr x, long i, mpfr_exp_t e, mpfr_rnd_t rnd_mode)
  29 {
  30   if (i == 0)
  31     {
  32       MPFR_SET_ZERO (x);
  33       MPFR_SET_POS (x);
  34       MPFR_RET (0);
  35     }
  36   else
  37     {
  38       mp_size_t xn;
  39       unsigned int cnt, nbits;
  40       mp_limb_t ai, *xp;
  41       int inex = 0;
  42
  43       /* FIXME: support int limbs (e.g. 16-bit limbs on 16-bit proc) */
  44       ai = SAFE_ABS (unsigned long, i);
  45       MPFR_ASSERTN (SAFE_ABS (unsigned long, i) == ai);
  46
  47       /* Position of the highest limb */
  48       xn = (MPFR_PREC (x) - 1) / GMP_NUMB_BITS;
  49       count_leading_zeros (cnt, ai);
  50       MPFR_ASSERTD (cnt < GMP_NUMB_BITS);  /* OK since i != 0 */
  51
  52       xp = MPFR_MANT(x);
  53       xp[xn] = ai << cnt;
  54       /* Zero the xn lower limbs. */
  55       MPN_ZERO(xp, xn);
  56       MPFR_SET_SIGN (x, i < 0 ? MPFR_SIGN_NEG : MPFR_SIGN_POS);
  57
  58       nbits = GMP_NUMB_BITS - cnt;
  59       e += nbits;  /* exponent _before_ the rounding */
  60
  61       /* round if MPFR_PREC(x) smaller than length of i */
  62       if (MPFR_UNLIKELY (MPFR_PREC (x) < nbits) &&
  63           MPFR_UNLIKELY (mpfr_round_raw (xp + xn, xp + xn, nbits, i < 0,
  64                                          MPFR_PREC (x), rnd_mode, &inex)))
  65         {
  66           e++;
  67           xp[xn] = MPFR_LIMB_HIGHBIT;
  68         }
  69
  70       MPFR_EXP (x) = e;
  71       return mpfr_check_range (x, inex, rnd_mode);
  72     }
  73 }