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46 lines
1.1 KiB
C++
46 lines
1.1 KiB
C++
17 years ago
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/* $Id$ */
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/** @file bitmath_func.cpp */
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#include "../stdafx.h"
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#include "bitmath_func.hpp"
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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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* conguence 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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* @param 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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