feat(add): support int128 + - * / (#10)

* try to support i128 add

* try to adopt int128 & uint128 from abseil-cpp 

* add int128 add test

* add int128 mul test

* support int128 div operation

CMakeLists.txt

@@ -18,7 +18,7 @@ set(THIRD_PARTY_INCLUDE_DIR
 
 include_directories(${SRC_INCLUDE_DIR}  ${THIRD_PARTY_INCLUDE_DIR})
 
-# add_subdirectory(src)
+add_subdirectory(src)
 add_subdirectory(examples)
 add_subdirectory(third_party)
 add_subdirectory(test)

src/CMakeLists.txt

@@ -1,3 +1,5 @@
+add_subdirectory(numbers)
+
 add_library(numbers_lib STATIC ${ALL_OBJECT_FILES})
 
 find_package(Threads REQUIRED)

src/include/bits.hh

@@ -0,0 +1,39 @@
+#ifndef NUMBERS_BITS_HH
+#define NUMBERS_BITS_HH
+
+#include <type_traits>
+
+#include "internal/config.h"
+#include "internal/bits.hh"
+
+#if NUMBERS_INTERNAL_CPLUSPLUS_LANG >= 202002L
+#include <bit>
+#endif
+
+// check if the compiler supports <bit> header
+#if defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L
+
+using std::countl_one;
+using std::countl_zero;
+
+#else
+
+// Counting functions
+//
+// While these functions are typically constexpr, on some platforms, they may
+// not be marked as constexpr due to constraints of the compiler/available
+// intrinsics.
+template <class T>
+inline typename std::enable_if<std::is_unsigned_v<T>, int>::type countl_zero(T x) noexcept {
+  return numbers_internal::count_leading_zeroes(x);
+}
+
+template <class T>
+inline typename std::enable_if<std::is_unsigned_v<T>, int>::type countl_one(T x) noexcept {
+  // Avoid integer promotion to a wider type
+  return countl_zero(static_cast<T>(~x));
+}
+
+#endif
+
+#endif