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1d92226b JJ |
1 | /* mpn_lshift -- Shift left low level. |
2 | ||
1b78544f | 3 | Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc. |
1d92226b JJ |
4 | |
5 | This file is part of the GNU MP Library. | |
6 | ||
7 | The GNU MP Library is free software; you can redistribute it and/or modify | |
8 | it under the terms of the GNU Lesser General Public License as published by | |
9 | the Free Software Foundation; either version 2.1 of the License, or (at your | |
10 | option) any later version. | |
11 | ||
12 | The GNU MP Library is distributed in the hope that it will be useful, but | |
13 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY | |
14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public | |
15 | License for more details. | |
16 | ||
17 | You should have received a copy of the GNU Lesser General Public License | |
18 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to | |
19 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, | |
20 | MA 02111-1307, USA. */ | |
21 | ||
a855debf | 22 | #include <config.h> |
1d92226b JJ |
23 | #include "gmp-impl.h" |
24 | ||
25 | /* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left | |
26 | and store the USIZE least significant digits of the result at WP. | |
27 | Return the bits shifted out from the most significant digit. | |
28 | ||
29 | Argument constraints: | |
30 | 1. 0 < CNT < BITS_PER_MP_LIMB | |
31 | 2. If the result is to be written over the input, WP must be >= UP. | |
32 | */ | |
33 | ||
34 | mp_limb_t | |
35 | #if __STDC__ | |
36 | mpn_lshift (register mp_ptr wp, | |
37 | register mp_srcptr up, mp_size_t usize, | |
38 | register unsigned int cnt) | |
39 | #else | |
40 | mpn_lshift (wp, up, usize, cnt) | |
41 | register mp_ptr wp; | |
42 | register mp_srcptr up; | |
43 | mp_size_t usize; | |
44 | register unsigned int cnt; | |
45 | #endif | |
46 | { | |
47 | register mp_limb_t high_limb, low_limb; | |
48 | register unsigned sh_1, sh_2; | |
49 | register mp_size_t i; | |
50 | mp_limb_t retval; | |
51 | ||
52 | #ifdef DEBUG | |
53 | if (usize == 0 || cnt == 0) | |
54 | abort (); | |
55 | #endif | |
56 | ||
57 | sh_1 = cnt; | |
58 | #if 0 | |
59 | if (sh_1 == 0) | |
60 | { | |
61 | if (wp != up) | |
62 | { | |
63 | /* Copy from high end to low end, to allow specified input/output | |
64 | overlapping. */ | |
65 | for (i = usize - 1; i >= 0; i--) | |
66 | wp[i] = up[i]; | |
67 | } | |
68 | return 0; | |
69 | } | |
70 | #endif | |
71 | ||
72 | wp += 1; | |
73 | sh_2 = BITS_PER_MP_LIMB - sh_1; | |
74 | i = usize - 1; | |
75 | low_limb = up[i]; | |
76 | retval = low_limb >> sh_2; | |
77 | high_limb = low_limb; | |
78 | while (--i >= 0) | |
79 | { | |
80 | low_limb = up[i]; | |
81 | wp[i] = (high_limb << sh_1) | (low_limb >> sh_2); | |
82 | high_limb = low_limb; | |
83 | } | |
84 | wp[i] = high_limb << sh_1; | |
85 | ||
86 | return retval; | |
87 | } |