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Use std::countl_zero instead of __builtin_clz #7025

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Use std::countl_zero instead of __builtin_clz #7025

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40 changes: 7 additions & 33 deletions include/util/msb.hpp
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Original file line number Diff line number Diff line change
@@ -1,50 +1,24 @@
#ifndef OSRM_UTIL_MSB_HPP
#define OSRM_UTIL_MSB_HPP

#include <bit>
#include <boost/assert.hpp>

#include <climits>
#include <cstdint>
#include <utility>
#include <limits>

namespace osrm::util
{

// get the msb of an integer
// return 0 for integers without msb
template <typename T> std::size_t msb(T value)
{
BOOST_ASSERT(value > 0);

static_assert(std::is_integral<T>::value && !std::is_signed<T>::value, "Integer required.");
std::size_t msb = 0;
while (value > 0)
{
value >>= 1u;
msb++;
}
BOOST_ASSERT(msb > 0);
return msb - 1;
}
constexpr auto MSB_INDEX = std::numeric_limits<unsigned char>::digits * sizeof(T) - 1;

#if (defined(__clang__) || defined(__GNUC__) || defined(__GNUG__))
inline std::size_t msb(unsigned long long v)
{
BOOST_ASSERT(v > 0);
constexpr auto MSB_INDEX = CHAR_BIT * sizeof(unsigned long long) - 1;
return MSB_INDEX - __builtin_clzll(v);
}
inline std::size_t msb(unsigned long v)
{
BOOST_ASSERT(v > 0);
constexpr auto MSB_INDEX = CHAR_BIT * sizeof(unsigned long) - 1;
return MSB_INDEX - __builtin_clzl(v);
}
inline std::size_t msb(unsigned int v)
{
BOOST_ASSERT(v > 0);
constexpr auto MSB_INDEX = CHAR_BIT * sizeof(unsigned int) - 1;
return MSB_INDEX - __builtin_clz(v);
return MSB_INDEX - std::countl_zero(value);
}
#endif

} // namespace osrm::util

#endif