OpenTTD Source: src/core/bitmath_func.cpp Source File

OpenTTD Source 12.2

bitmath_func.cpp
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1 /*
2 * This file is part of OpenTTD.
3 * OpenTTD 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.
4 * OpenTTD 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.
5 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
6 */
7
10 #include "../stdafx.h"
11 #include "bitmath_func.hpp"
12
13 #include "../safeguards.h"
14
15 const uint8 _ffb_64[64] = {
16 0, 0, 1, 0, 2, 0, 1, 0,
17 3, 0, 1, 0, 2, 0, 1, 0,
18 4, 0, 1, 0, 2, 0, 1, 0,
19 3, 0, 1, 0, 2, 0, 1, 0,
20 5, 0, 1, 0, 2, 0, 1, 0,
21 3, 0, 1, 0, 2, 0, 1, 0,
22 4, 0, 1, 0, 2, 0, 1, 0,
23 3, 0, 1, 0, 2, 0, 1, 0,
24 };
25
37 uint8 FindFirstBit(uint64 x)
38 {
39 if (x == 0) return 0;
40 /* The macro FIND_FIRST_BIT is better to use when your x is
41 not more than 128. */
42
43 uint8 pos = 0;
44
45 if ((x & 0xffffffffULL) == 0) { x >>= 32; pos += 32; }
46 if ((x & 0x0000ffffULL) == 0) { x >>= 16; pos += 16; }
47 if ((x & 0x000000ffULL) == 0) { x >>= 8; pos += 8; }
48 if ((x & 0x0000000fULL) == 0) { x >>= 4; pos += 4; }
49 if ((x & 0x00000003ULL) == 0) { x >>= 2; pos += 2; }
50 if ((x & 0x00000001ULL) == 0) { pos += 1; }
51
52 return pos;
53 }
54
66 uint8 FindLastBit(uint64 x)
67 {
68 if (x == 0) return 0;
69
70 uint8 pos = 0;
71
72 if ((x & 0xffffffff00000000ULL) != 0) { x >>= 32; pos += 32; }
73 if ((x & 0x00000000ffff0000ULL) != 0) { x >>= 16; pos += 16; }
74 if ((x & 0x000000000000ff00ULL) != 0) { x >>= 8; pos += 8; }
75 if ((x & 0x00000000000000f0ULL) != 0) { x >>= 4; pos += 4; }
76 if ((x & 0x000000000000000cULL) != 0) { x >>= 2; pos += 2; }
77 if ((x & 0x0000000000000002ULL) != 0) { pos += 1; }
78
79 return pos;
80 }
FindLastBit
uint8 FindLastBit(uint64 x)
Search the last set bit in a 64 bit variable.
Definition: bitmath_func.cpp:66
FindFirstBit
uint8 FindFirstBit(uint64 x)
Search the first set bit in a 64 bit variable.
Definition: bitmath_func.cpp:37
bitmath_func.hpp
_ffb_64
const uint8 _ffb_64[64]
Lookup table to check which bit is set in a 6 bit variable.
Definition: bitmath_func.cpp:15