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
|
/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
* vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
*
* Copyright (C) 2008, 2009 Sun Microsystems, Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program 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 a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
/*
Some useful bit functions
*/
#pragma once
namespace drizzled
{
namespace internal
{
extern const char _my_bits_nbits[256];
extern const unsigned char _my_bits_reverse_table[256];
/*
Find smallest X in 2^X >= value
This can be used to divide a number with value by doing a shift instead
*/
static inline uint32_t my_bit_log2(uint32_t value)
{
uint32_t bit;
for (bit=0 ; value > 1 ; value>>=1, bit++) ;
return bit;
}
static inline uint32_t my_count_bits(uint64_t v)
{
/* The following code is a bit faster on 16 bit machines than if we would
only shift v */
uint32_t v2=(uint32_t) (v >> 32);
return (uint32_t) (unsigned char) (_my_bits_nbits[(unsigned char) v] +
_my_bits_nbits[(unsigned char) (v >> 8)] +
_my_bits_nbits[(unsigned char) (v >> 16)] +
_my_bits_nbits[(unsigned char) (v >> 24)] +
_my_bits_nbits[(unsigned char) (v2)] +
_my_bits_nbits[(unsigned char) (v2 >> 8)] +
_my_bits_nbits[(unsigned char) (v2 >> 16)] +
_my_bits_nbits[(unsigned char) (v2 >> 24)]);
}
static inline uint32_t my_count_bits_uint16(uint16_t v)
{
return _my_bits_nbits[v];
}
static inline uint32_t my_clear_highest_bit(uint32_t v)
{
uint32_t w=v >> 1;
w|= w >> 1;
w|= w >> 2;
w|= w >> 4;
w|= w >> 8;
w|= w >> 16;
return v & w;
}
static inline uint32_t my_reverse_bits(uint32_t key)
{
return
(_my_bits_reverse_table[ key & 255] << 24) |
(_my_bits_reverse_table[(key>> 8) & 255] << 16) |
(_my_bits_reverse_table[(key>>16) & 255] << 8) |
_my_bits_reverse_table[(key>>24) ];
}
} /* namespace internal */
} /* namespace drizzled */
|