1/* mpn_lshiftc -- Shift left low level with complement.
2
3Copyright 1991, 1993, 1994, 1996, 2000-2002, 2009 Free Software Foundation,
4Inc.
5
6This file is part of the GNU MP Library.
7
8The GNU MP Library is free software; you can redistribute it and/or modify
9it under the terms of either:
10
11  * the GNU Lesser General Public License as published by the Free
12    Software Foundation; either version 3 of the License, or (at your
13    option) any later version.
14
15or
16
17  * the GNU General Public License as published by the Free Software
18    Foundation; either version 2 of the License, or (at your option) any
19    later version.
20
21or both in parallel, as here.
22
23The GNU MP Library is distributed in the hope that it will be useful, but
24WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
25or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
26for more details.
27
28You should have received copies of the GNU General Public License and the
29GNU Lesser General Public License along with the GNU MP Library.  If not,
30see https://www.gnu.org/licenses/.  */
31
32#include "gmp-impl.h"
33
34/* Shift U (pointed to by up and n limbs long) cnt bits to the left
35   and store the n least significant limbs of the result at rp.
36   Return the bits shifted out from the most significant limb.
37
38   Argument constraints:
39   1. 0 < cnt < GMP_NUMB_BITS.
40   2. If the result is to be written over the input, rp must be >= up.
41*/
42
43mp_limb_t
44mpn_lshiftc (mp_ptr rp, mp_srcptr up, mp_size_t n, unsigned int cnt)
45{
46  mp_limb_t high_limb, low_limb;
47  unsigned int tnc;
48  mp_size_t i;
49  mp_limb_t retval;
50
51  ASSERT (n >= 1);
52  ASSERT (cnt >= 1);
53  ASSERT (cnt < GMP_NUMB_BITS);
54  ASSERT (MPN_SAME_OR_DECR_P (rp, up, n));
55
56  up += n;
57  rp += n;
58
59  tnc = GMP_NUMB_BITS - cnt;
60  low_limb = *--up;
61  retval = low_limb >> tnc;
62  high_limb = (low_limb << cnt);
63
64  for (i = n - 1; i != 0; i--)
65    {
66      low_limb = *--up;
67      *--rp = (~(high_limb | (low_limb >> tnc))) & GMP_NUMB_MASK;
68      high_limb = low_limb << cnt;
69    }
70  *--rp = (~high_limb) & GMP_NUMB_MASK;
71
72  return retval;
73}
74