OpenTTD
bitmath_func.cpp
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1 /* $Id: bitmath_func.cpp 26482 2014-04-23 20:13:33Z rubidium $ */
2 
3 /*
4  * This file is part of OpenTTD.
5  * 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.
6  * 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.
7  * 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/>.
8  */
9 
12 #include "../stdafx.h"
13 #include "bitmath_func.hpp"
14 
15 #include "../safeguards.h"
16 
17 const uint8 _ffb_64[64] = {
18  0, 0, 1, 0, 2, 0, 1, 0,
19  3, 0, 1, 0, 2, 0, 1, 0,
20  4, 0, 1, 0, 2, 0, 1, 0,
21  3, 0, 1, 0, 2, 0, 1, 0,
22  5, 0, 1, 0, 2, 0, 1, 0,
23  3, 0, 1, 0, 2, 0, 1, 0,
24  4, 0, 1, 0, 2, 0, 1, 0,
25  3, 0, 1, 0, 2, 0, 1, 0,
26 };
27 
39 uint8 FindFirstBit(uint32 x)
40 {
41  if (x == 0) return 0;
42  /* The macro FIND_FIRST_BIT is better to use when your x is
43  not more than 128. */
44 
45  uint8 pos = 0;
46 
47  if ((x & 0x0000ffff) == 0) { x >>= 16; pos += 16; }
48  if ((x & 0x000000ff) == 0) { x >>= 8; pos += 8; }
49  if ((x & 0x0000000f) == 0) { x >>= 4; pos += 4; }
50  if ((x & 0x00000003) == 0) { x >>= 2; pos += 2; }
51  if ((x & 0x00000001) == 0) { pos += 1; }
52 
53  return pos;
54 }
55 
67 uint8 FindLastBit(uint64 x)
68 {
69  if (x == 0) return 0;
70 
71  uint8 pos = 0;
72 
73  if ((x & 0xffffffff00000000ULL) != 0) { x >>= 32; pos += 32; }
74  if ((x & 0x00000000ffff0000ULL) != 0) { x >>= 16; pos += 16; }
75  if ((x & 0x000000000000ff00ULL) != 0) { x >>= 8; pos += 8; }
76  if ((x & 0x00000000000000f0ULL) != 0) { x >>= 4; pos += 4; }
77  if ((x & 0x000000000000000cULL) != 0) { x >>= 2; pos += 2; }
78  if ((x & 0x0000000000000002ULL) != 0) { pos += 1; }
79 
80  return pos;
81 }
Functions related to bit mathematics.
const uint8 _ffb_64[64]
Lookup table to check which bit is set in a 6 bit variable.
uint8 FindLastBit(uint64 x)
Search the last set bit in a 64 bit variable.
uint8 FindFirstBit(uint32 x)
Search the first set bit in a 32 bit variable.