1/* mpz_mul_2exp -- Multiply a bignum by 2**CNT
2
3Copyright 1991, 1993, 1994, 1996, 2001, 2002 Free Software Foundation, Inc.
4
5This file is part of the GNU MP Library.
6
7The GNU MP Library is free software; you can redistribute it and/or modify
8it under the terms of the GNU Lesser General Public License as published by
9the Free Software Foundation; either version 3 of the License, or (at your
10option) any later version.
11
12The GNU MP Library is distributed in the hope that it will be useful, but
13WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
15License for more details.
16
17You should have received a copy of the GNU Lesser General Public License
18along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
19
20#include "gmp.h"
21#include "gmp-impl.h"
22
23void
24mpz_mul_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
25{
26  mp_size_t usize = u->_mp_size;
27  mp_size_t abs_usize = ABS (usize);
28  mp_size_t wsize;
29  mp_size_t limb_cnt;
30  mp_ptr wp;
31  mp_limb_t wlimb;
32
33  if (usize == 0)
34    {
35      w->_mp_size = 0;
36      return;
37    }
38
39  limb_cnt = cnt / GMP_NUMB_BITS;
40  wsize = abs_usize + limb_cnt + 1;
41  if (w->_mp_alloc < wsize)
42    _mpz_realloc (w, wsize);
43
44  wp = w->_mp_d;
45  wsize = abs_usize + limb_cnt;
46
47  cnt %= GMP_NUMB_BITS;
48  if (cnt != 0)
49    {
50      wlimb = mpn_lshift (wp + limb_cnt, u->_mp_d, abs_usize, cnt);
51      if (wlimb != 0)
52	{
53	  wp[wsize] = wlimb;
54	  wsize++;
55	}
56    }
57  else
58    {
59      MPN_COPY_DECR (wp + limb_cnt, u->_mp_d, abs_usize);
60    }
61
62  /* Zero all whole limbs at low end.  Do it here and not before calling
63     mpn_lshift, not to lose for U == W.  */
64  MPN_ZERO (wp, limb_cnt);
65
66  w->_mp_size = usize >= 0 ? wsize : -wsize;
67}
68