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/*************************************************
* Bit/Word Operations Header File *
* (C) 1999-2008 Jack Lloyd *
*************************************************/
#ifndef BOTAN_BIT_OPS_H__
#define BOTAN_BIT_OPS_H__
#include <botan/types.h>
namespace Botan {
/*************************************************
* Return true iff arg is 2**n for some n > 0 *
* T should be an unsigned integer type *
*************************************************/
template<typename T>
inline bool power_of_2(T arg)
{
return ((arg != 0 && arg != 1) && ((arg & (arg-1)) == 0));
}
/*************************************************
* Return the index of the highest set bit
* T is an unsigned integer type
*************************************************/
template<typename T>
inline u32bit high_bit(T n)
{
for(u32bit i = 8*sizeof(T); i > 0; --i)
if((n >> (i - 1)) & 0x01)
return i;
return 0;
}
/*************************************************
* Return the index of the lowest set bit *
*************************************************/
template<typename T>
inline u32bit low_bit(T n)
{
for(u32bit i = 0; i != 8*sizeof(T); ++i)
if((n >> i) & 0x01)
return (i + 1);
return 0;
}
/*************************************************
* Return the number of significant bytes in n *
*************************************************/
template<typename T>
inline u32bit significant_bytes(T n)
{
for(u32bit j = 0; j != sizeof(T); ++j)
if(get_byte(j, n))
return sizeof(T)-j;
return 0;
}
/*************************************************
* Return the Hamming weight of n *
*************************************************/
template<typename T>
inline u32bit hamming_weight(T n)
{
const byte NIBBLE_WEIGHTS[] = {
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4 };
u32bit weight = 0;
for(u32bit i = 0; i != 2*sizeof(T); ++i)
weight += NIBBLE_WEIGHTS[(n >> (4*i)) & 0x0F];
return weight;
}
/*************************************************
* Count the trailing zero bits in n *
*************************************************/
template<typename T>
inline u32bit ctz(T n)
{
for(int i = 0; i != 8*sizeof(T); ++i)
if((n >> i) & 0x01)
return i;
return 8*sizeof(T);
}
}
#endif
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