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/*
* Copyright (C) 2013 Freie Universitรคt Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup core_util
* @{
*
* @file
* @brief Bit arithmetic helper functions implementation
*
* @author Kaspar Schleiser <kaspar@schleiser.de>
* @author Martine Lenders <mlenders@inf.fu-berlin.de>
*
* @}
*/
#include <stdio.h>
unsigned bitarithm_msb(unsigned v)
{
register unsigned r; // result of log2(v) will go here
#if ARCH_32_BIT
register unsigned shift;
r = (v > 0xFFFF) << 4; v >>= r;
shift = (v > 0xFF ) << 3; v >>= shift; r |= shift;
shift = (v > 0xF ) << 2; v >>= shift; r |= shift;
shift = (v > 0x3 ) << 1; v >>= shift; r |= shift;
r |= (v >> 1);
#else
r = 0;
while (v >>= 1) { // unroll for more speed...
r++;
}
#endif
return r;
}
/*---------------------------------------------------------------------------*/
unsigned bitarithm_lsb(register unsigned v)
{
register unsigned r = 0;
while ((v & 0x01) == 0) {
v >>= 1;
r++;
};
return r;
}
/*---------------------------------------------------------------------------*/
unsigned bitarithm_bits_set(unsigned v)
{
unsigned c; // c accumulates the total bits set in v
for (c = 0; v; c++) {
v &= v - 1; // clear the least significant bit set
}
return c;
}
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