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/* $Id$ */
/*
* This file is part of OpenTTD.
* 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.
* 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.
* 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/>.
*/
/** @file bitmath_func.cpp Functions related to bit mathematics. */
#include "../stdafx.h"
#include "bitmath_func.hpp"
const uint8 _ffb_64[64] = {
0, 0, 1, 0, 2, 0, 1, 0,
3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0,
3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0,
3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0,
3, 0, 1, 0, 2, 0, 1, 0,
};
/**
* Search the first set bit in a 32 bit variable.
*
* This algorithm is a static implementation of a log
* conguence search algorithm. It checks the first half
* if there is a bit set search there further. And this
* way further. If no bit is set return 0.
*
* @param x The value to search
* @return The position of the first bit set
*/
uint8 FindFirstBit(uint32 x)
{
if (x == 0) return 0;
/* The macro FIND_FIRST_BIT is better to use when your x is
not more than 128. */
uint8 pos = 0;
if ((x & 0x0000ffff) == 0) { x >>= 16; pos += 16; }
if ((x & 0x000000ff) == 0) { x >>= 8; pos += 8; }
if ((x & 0x0000000f) == 0) { x >>= 4; pos += 4; }
if ((x & 0x00000003) == 0) { x >>= 2; pos += 2; }
if ((x & 0x00000001) == 0) { pos += 1; }
return pos;
}
/**
* Search the last set bit in a 64 bit variable.
*
* This algorithm is a static implementation of a log
* conguence search algorithm. It checks the second half
* if there is a bit set search there further. And this
* way further. If no bit is set return 0.
*
* @param x The value to search
* @return The position of the last bit set
*/
uint8 FindLastBit(uint64 x)
{
if (x == 0) return 0;
uint8 pos = 0;
if ((x & 0xffffffff00000000ULL) != 0) { x >>= 32; pos += 32; }
if ((x & 0x00000000ffff0000ULL) != 0) { x >>= 16; pos += 16; }
if ((x & 0x000000000000ff00ULL) != 0) { x >>= 8; pos += 8; }
if ((x & 0x00000000000000f0ULL) != 0) { x >>= 4; pos += 4; }
if ((x & 0x000000000000000cULL) != 0) { x >>= 2; pos += 2; }
if ((x & 0x0000000000000002ULL) != 0) { pos += 1; }
return pos;
}
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