/* $Id$ */ /* * 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; }