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/*************************************************
* Bit/Word Operations Source File *
* (C) 1999-2008 Jack Lloyd *
*************************************************/
#include <botan/bit_ops.h>
#include <botan/loadstor.h>
namespace Botan {
/*************************************************
* Return true iff arg is 2**n for some n > 0 *
*************************************************/
bool power_of_2(u64bit arg)
{
if(arg == 0 || arg == 1)
return false;
if((arg & (arg-1)) == 0)
return true;
return false;
}
/*************************************************
* Return the index of the highest set bit *
*************************************************/
u32bit high_bit(u64bit n)
{
for(u32bit count = 64; count > 0; --count)
if((n >> (count - 1)) & 0x01)
return count;
return 0;
}
/*************************************************
* Return the index of the lowest set bit *
*************************************************/
u32bit low_bit(u64bit n)
{
for(u32bit count = 0; count != 64; ++count)
if((n >> count) & 0x01)
return (count + 1);
return 0;
}
/*************************************************
* Return the number of significant bytes in n *
*************************************************/
u32bit significant_bytes(u64bit n)
{
for(u32bit j = 0; j != 8; ++j)
if(get_byte(j, n))
return 8-j;
return 0;
}
/*************************************************
* Return the Hamming weight of n *
*************************************************/
u32bit hamming_weight(u64bit n)
{
u32bit weight = 0;
for(u32bit j = 0; j != 64; ++j)
if((n >> j) & 0x01)
++weight;
return weight;
}
}
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