author | rubidium |
Sun, 02 Dec 2007 19:21:56 +0000 | |
changeset 8000 | 2ba28bc428f1 |
parent 7971 | 8509d595142a |
child 8005 | 2318a0547719 |
permissions | -rw-r--r-- |
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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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* @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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/** |
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* Search the last 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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* @return The position of the last bit set |
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*/ |
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uint8 FindLastBit(uint32 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 & 0xffff0000) != 0) { x >>= 16; pos += 16; } |
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if ((x & 0x0000ff00) != 0) { x >>= 8; pos += 8; } |
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if ((x & 0x000000f0) != 0) { x >>= 4; pos += 4; } |
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if ((x & 0x0000000c) != 0) { x >>= 2; pos += 2; } |
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if ((x & 0x00000002) != 0) { pos += 1; } |
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return pos; |
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} |