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6b628d36 | 1 | /* mpn_rshift -- Shift right a low-level natural-number integer. |
28f540f4 | 2 | |
04277e02 | 3 | Copyright (C) 1991-2019 Free Software Foundation, Inc. |
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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 | |
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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 | |
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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 | |
6d84f89a | 14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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15 | License for more details. |
16 | ||
6d84f89a | 17 | You should have received a copy of the GNU Lesser General Public License |
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18 | along with the GNU MP Library; see the file COPYING.LIB. If not, see |
19 | <http://www.gnu.org/licenses/>. */ | |
28f540f4 | 20 | |
9d13fb24 | 21 | #include <gmp.h> |
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22 | #include "gmp-impl.h" |
23 | ||
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24 | #include <assert.h> |
25 | ||
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26 | /* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right |
27 | and store the USIZE least significant limbs of the result at WP. | |
28 | The bits shifted out to the right are returned. | |
29 | ||
30 | Argument constraints: | |
31 | 1. 0 < CNT < BITS_PER_MP_LIMB | |
32 | 2. If the result is to be written over the input, WP must be <= UP. | |
33 | */ | |
34 | ||
b928942e | 35 | mp_limb_t |
6b628d36 | 36 | mpn_rshift (register mp_ptr wp, |
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37 | register mp_srcptr up, mp_size_t usize, |
38 | register unsigned int cnt) | |
28f540f4 | 39 | { |
b928942e | 40 | register mp_limb_t high_limb, low_limb; |
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41 | register unsigned sh_1, sh_2; |
42 | register mp_size_t i; | |
b928942e | 43 | mp_limb_t retval; |
28f540f4 | 44 | |
f2b3078e | 45 | assert (usize != 0 && cnt != 0); |
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46 | |
47 | sh_1 = cnt; | |
48 | ||
49 | #if 0 | |
50 | if (sh_1 == 0) | |
51 | { | |
52 | if (wp != up) | |
53 | { | |
54 | /* Copy from low end to high end, to allow specified input/output | |
55 | overlapping. */ | |
56 | for (i = 0; i < usize; i++) | |
57 | wp[i] = up[i]; | |
58 | } | |
59 | return usize; | |
60 | } | |
61 | #endif | |
62 | ||
63 | wp -= 1; | |
64 | sh_2 = BITS_PER_MP_LIMB - sh_1; | |
65 | high_limb = up[0]; | |
66 | retval = high_limb << sh_2; | |
67 | low_limb = high_limb; | |
68 | ||
69 | for (i = 1; i < usize; i++) | |
70 | { | |
71 | high_limb = up[i]; | |
72 | wp[i] = (low_limb >> sh_1) | (high_limb << sh_2); | |
73 | low_limb = high_limb; | |
74 | } | |
75 | wp[i] = low_limb >> sh_1; | |
76 | ||
77 | return retval; | |
78 | } |