Use std::countl_zero instead of __builtin_clzll (Project-OSRM#7025)

Author: SiarheiFedartsou

include/util/msb.hpp

@@ -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