/src/gmp-6.2.1/mpn/gcd_1.c
Line | Count | Source |
1 | | /* mpn_gcd_1 -- mpn and limb greatest common divisor. |
2 | | |
3 | | Copyright 1994, 1996, 2000, 2001, 2009, 2012, 2019 Free Software Foundation, Inc. |
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 either: |
9 | | |
10 | | * the GNU Lesser General Public License as published by the Free |
11 | | Software Foundation; either version 3 of the License, or (at your |
12 | | option) any later version. |
13 | | |
14 | | or |
15 | | |
16 | | * the GNU General Public License as published by the Free Software |
17 | | Foundation; either version 2 of the License, or (at your option) any |
18 | | later version. |
19 | | |
20 | | or both in parallel, as here. |
21 | | |
22 | | The GNU MP Library is distributed in the hope that it will be useful, but |
23 | | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
24 | | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
25 | | for more details. |
26 | | |
27 | | You should have received copies of the GNU General Public License and the |
28 | | GNU Lesser General Public License along with the GNU MP Library. If not, |
29 | | see https://www.gnu.org/licenses/. */ |
30 | | |
31 | | #include "gmp-impl.h" |
32 | | #include "longlong.h" |
33 | | |
34 | | /* Does not work for U == 0 or V == 0. It would be tough to make it work for |
35 | | V == 0 since gcd(x,0) = x, and U does not generally fit in an mp_limb_t. |
36 | | |
37 | | The threshold for doing u%v when size==1 will vary by CPU according to |
38 | | the speed of a division and the code generated for the main loop. Any |
39 | | tuning for this is left to a CPU specific implementation. */ |
40 | | |
41 | | mp_limb_t |
42 | | mpn_gcd_1 (mp_srcptr up, mp_size_t size, mp_limb_t vlimb) |
43 | 176 | { |
44 | 176 | mp_limb_t ulimb; |
45 | 176 | unsigned long zero_bits, u_low_zero_bits; |
46 | 176 | int c; |
47 | | |
48 | 176 | ASSERT (size >= 1); |
49 | 176 | ASSERT (vlimb != 0); |
50 | 176 | ASSERT_MPN_NONZERO_P (up, size); |
51 | | |
52 | 176 | ulimb = up[0]; |
53 | | |
54 | | /* Need vlimb odd for modexact, want it odd to get common zeros. */ |
55 | 176 | count_trailing_zeros (zero_bits, vlimb); |
56 | 176 | vlimb >>= zero_bits; |
57 | | |
58 | 176 | if (size > 1) |
59 | 77 | { |
60 | | /* Must get common zeros before the mod reduction. If ulimb==0 then |
61 | | vlimb already gives the common zeros. */ |
62 | 77 | if (ulimb != 0) |
63 | 69 | { |
64 | 69 | count_trailing_zeros (u_low_zero_bits, ulimb); |
65 | 69 | zero_bits = MIN (zero_bits, u_low_zero_bits); |
66 | 69 | } |
67 | | |
68 | 77 | ulimb = MPN_MOD_OR_MODEXACT_1_ODD (up, size, vlimb); |
69 | 77 | if (ulimb == 0) |
70 | 8 | goto done; |
71 | | |
72 | 69 | count_trailing_zeros (c, ulimb); |
73 | 69 | ulimb >>= c; |
74 | 69 | } |
75 | 99 | else |
76 | 99 | { |
77 | | /* size==1, so up[0]!=0 */ |
78 | 99 | count_trailing_zeros (u_low_zero_bits, ulimb); |
79 | 99 | ulimb >>= u_low_zero_bits; |
80 | 99 | zero_bits = MIN (zero_bits, u_low_zero_bits); |
81 | | |
82 | | /* make u bigger */ |
83 | 99 | if (vlimb > ulimb) |
84 | 34 | MP_LIMB_T_SWAP (ulimb, vlimb); |
85 | | |
86 | | /* if u is much bigger than v, reduce using a division rather than |
87 | | chipping away at it bit-by-bit */ |
88 | 99 | if ((ulimb >> 16) > vlimb) |
89 | 74 | { |
90 | 74 | ulimb %= vlimb; |
91 | 74 | if (ulimb == 0) |
92 | 37 | goto done; |
93 | | |
94 | 37 | count_trailing_zeros (c, ulimb); |
95 | 37 | ulimb >>= c; |
96 | 37 | } |
97 | 99 | } |
98 | | |
99 | 131 | vlimb = mpn_gcd_11 (ulimb, vlimb); |
100 | | |
101 | 176 | done: |
102 | 176 | return vlimb << zero_bits; |
103 | 131 | } |