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66 lines
1.4 KiB
C
66 lines
1.4 KiB
C
/**
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* bit arithmetic helper functions
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*
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* Copyright (C) 2010 Freie Universität Berlin
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*
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* This file subject to the terms and conditions of the GNU General Public
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* License. See the file LICENSE in the top level directory for more details.
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*
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* \ingroup bitarithm
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* \{
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* \file
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* \author Kaspar Schleiser <kaspar.schleiser@fu-berlin.de>
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* \}
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*/
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#include <stdio.h>
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#define ARCH_32_BIT (__INT_MAX__ == 2147483647)
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unsigned
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number_of_highest_bit(unsigned v)
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{
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register unsigned r; // result of log2(v) will go here
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#if ARCH_32_BIT
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register unsigned shift;
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r = (v > 0xFFFF) << 4; v >>= r;
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shift = (v > 0xFF ) << 3; v >>= shift; r |= shift;
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shift = (v > 0xF ) << 2; v >>= shift; r |= shift;
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shift = (v > 0x3 ) << 1; v >>= shift; r |= shift;
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r |= (v >> 1);
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#else
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r = 0;
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while (v >>= 1) // unroll for more speed...
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r++;
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#endif
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return r;
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}
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/*---------------------------------------------------------------------------*/
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unsigned
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number_of_lowest_bit(register unsigned v)
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{
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register unsigned r = 0;
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while( (v & 0x01) == 0 ) {
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v >>= 1;
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r++;
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};
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return r;
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}
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/*---------------------------------------------------------------------------*/
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unsigned
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number_of_bits_set(unsigned v)
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{
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unsigned c; // c accumulates the total bits set in v
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for (c = 0; v; c++) {
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v &= v - 1; // clear the least significant bit set
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}
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return c;
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}
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