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89 lines
2.7 KiB
C++
89 lines
2.7 KiB
C++
/* $Id$ */
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/*
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* This file is part of OpenTTD.
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* 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.
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* 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.
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* 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/>.
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*/
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/** @file bitmath_func.cpp Functions related to bit mathematics. */
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#include "../stdafx.h"
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#include "bitmath_func.hpp"
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#include "../safeguards.h"
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const uint8 _ffb_64[64] = {
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0, 0, 1, 0, 2, 0, 1, 0,
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3, 0, 1, 0, 2, 0, 1, 0,
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4, 0, 1, 0, 2, 0, 1, 0,
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3, 0, 1, 0, 2, 0, 1, 0,
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5, 0, 1, 0, 2, 0, 1, 0,
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3, 0, 1, 0, 2, 0, 1, 0,
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4, 0, 1, 0, 2, 0, 1, 0,
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3, 0, 1, 0, 2, 0, 1, 0,
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};
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/**
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* Search the first set bit in a 32 bit variable.
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*
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* This algorithm is a static implementation of a log
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* congruence search algorithm. It checks the first half
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* if there is a bit set search there further. And this
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* way further. If no bit is set return 0.
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*
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* @param x The value to search
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* @return The position of the first bit set
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*/
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uint8 FindFirstBit(uint32 x)
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{
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if (x == 0) return 0;
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/* The macro FIND_FIRST_BIT is better to use when your x is
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not more than 128. */
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uint8 pos = 0;
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if ((x & 0x0000ffff) == 0) { x >>= 16; pos += 16; }
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if ((x & 0x000000ff) == 0) { x >>= 8; pos += 8; }
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if ((x & 0x0000000f) == 0) { x >>= 4; pos += 4; }
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if ((x & 0x00000003) == 0) { x >>= 2; pos += 2; }
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if ((x & 0x00000001) == 0) { pos += 1; }
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return pos;
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}
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uint8 FindFirstBit64(uint64 x)
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{
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if (x == 0) return 0;
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if ((x & 0x00000000ffffffffULL) != 0) return FindFirstBit(x);
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return FindFirstBit(x >> 32) + 32;
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}
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/**
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* Search the last set bit in a 64 bit variable.
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*
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* This algorithm is a static implementation of a log
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* congruence search algorithm. It checks the second half
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* if there is a bit set search there further. And this
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* way further. If no bit is set return 0.
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*
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* @param x The value to search
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* @return The position of the last bit set
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*/
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uint8 FindLastBit(uint64 x)
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{
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if (x == 0) return 0;
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uint8 pos = 0;
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if ((x & 0xffffffff00000000ULL) != 0) { x >>= 32; pos += 32; }
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if ((x & 0x00000000ffff0000ULL) != 0) { x >>= 16; pos += 16; }
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if ((x & 0x000000000000ff00ULL) != 0) { x >>= 8; pos += 8; }
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if ((x & 0x00000000000000f0ULL) != 0) { x >>= 4; pos += 4; }
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if ((x & 0x000000000000000cULL) != 0) { x >>= 2; pos += 2; }
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if ((x & 0x0000000000000002ULL) != 0) { pos += 1; }
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return pos;
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}
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