1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
/* mpz_hamdist -- calculate hamming distance.
Copyright 1994, 1996, 2001, 2002, 2009-2011 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of either:
* the GNU Lesser General Public License as published by the Free
Software Foundation; either version 3 of the License, or (at your
option) any later version.
or
* the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any
later version.
or both in parallel, as here.
The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received copies of the GNU General Public License and the
GNU Lesser General Public License along with the GNU MP Library. If not,
see https://www.gnu.org/licenses/. */
#include "gmp-impl.h"
mp_bitcnt_t
mpz_hamdist (mpz_srcptr u, mpz_srcptr v) __GMP_NOTHROW
{
mp_srcptr up, vp;
mp_size_t usize, vsize;
mp_bitcnt_t count;
usize = SIZ(u);
vsize = SIZ(v);
up = PTR(u);
vp = PTR(v);
if (usize >= 0)
{
if (vsize < 0)
return ~ (mp_bitcnt_t) 0;
/* positive/positive */
if (usize < vsize)
MPN_SRCPTR_SWAP (up,usize, vp,vsize);
count = 0;
if (vsize != 0)
count = mpn_hamdist (up, vp, vsize);
usize -= vsize;
if (usize != 0)
count += mpn_popcount (up + vsize, usize);
return count;
}
else
{
mp_limb_t ulimb, vlimb;
mp_size_t old_vsize, step;
if (vsize >= 0)
return ~ (mp_bitcnt_t) 0;
/* negative/negative */
usize = -usize;
vsize = -vsize;
/* skip common low zeros */
for (;;)
{
ASSERT (usize > 0);
ASSERT (vsize > 0);
usize--;
vsize--;
ulimb = *up++;
vlimb = *vp++;
if (ulimb != 0)
break;
if (vlimb != 0)
{
MPN_SRCPTR_SWAP (up,usize, vp,vsize);
ulimb = vlimb;
vlimb = 0;
break;
}
}
/* twos complement first non-zero limbs (ulimb is non-zero, but vlimb
might be zero) */
ulimb = -ulimb;
vlimb = -vlimb;
popc_limb (count, (ulimb ^ vlimb) & GMP_NUMB_MASK);
if (vlimb == 0)
{
mp_bitcnt_t twoscount;
/* first non-zero of v */
old_vsize = vsize;
do
{
ASSERT (vsize > 0);
vsize--;
vlimb = *vp++;
}
while (vlimb == 0);
/* part of u corresponding to skipped v zeros */
step = old_vsize - vsize - 1;
count += step * GMP_NUMB_BITS;
step = MIN (step, usize);
if (step != 0)
{
count -= mpn_popcount (up, step);
usize -= step;
up += step;
}
/* First non-zero vlimb as twos complement, xor with ones
complement ulimb. Note -v^(~0^u) == (v-1)^u. */
vlimb--;
if (usize != 0)
{
usize--;
vlimb ^= *up++;
}
popc_limb (twoscount, vlimb);
count += twoscount;
}
/* Overlapping part of u and v, if any. Ones complement both, so just
plain hamdist. */
step = MIN (usize, vsize);
if (step != 0)
{
count += mpn_hamdist (up, vp, step);
usize -= step;
vsize -= step;
up += step;
vp += step;
}
/* Remaining high part of u or v, if any, ones complement but xor
against all ones in the other, so plain popcount. */
if (usize != 0)
{
remaining:
count += mpn_popcount (up, usize);
}
else if (vsize != 0)
{
up = vp;
usize = vsize;
goto remaining;
}
return count;
}
}
|
