pow2.h

#pragma once
#include <cstddef>
 
// constexpr functions
namespace tinker {
constexpr bool isPow2(size_t val)
{
   return (val != 0) && ((val & (val - 1)) == 0);
}
 
constexpr int pow2(int val)
{
   return 1 << val;
}
 
constexpr long long pow2ll(int val)
{
   return 1ll << val;
}
 
constexpr int floorLog2_constexpr(size_t val)
{
   return val < 2 ? 0 : 1 + floorLog2_constexpr(val >> 1);
}
 
constexpr size_t pow2Le(size_t val)
{
   return 1ull << floorLog2_constexpr(val);
}
 
constexpr size_t pow2Ge(size_t val)
{
   return val <= 1 ? 1 : (1ull << (1 + floorLog2_constexpr(val - 1)));
}
}
 
// inline functions
namespace tinker {
inline int floorLog2(int val)
{
   if (val == 0) return 0;
   int c = __builtin_clz(val);
   return 8 * sizeof(int) - 1 - c;
}
 
inline int floorLog2(long long val)
{
   if (val == 0) return 0;
   int c = __builtin_clzll(val);
   return 8 * sizeof(long long) - 1 - c;
}
 
inline int ceilLog2(int val)
{
   return floorLog2(val) + (val & (val - 1) ? 1 : 0);
}
 
inline int ceilLog2(long long val)
{
   return floorLog2(val) + (val & (val - 1) ? 1 : 0);
}
}