RAPIDJSON_NAMESPACE_BEGIN
namespace internal {

inline uint32_t clzll(uint64_t x) {
    // Passing 0 to __builtin_clzll is UB in GCC and results in an
    // infinite loop in the software implementation.
    RAPIDJSON_ASSERT(x != 0);

#if defined(_MSC_VER) && !defined(UNDER_CE)
    unsigned long r = 0;
#if defined(_WIN64)
    _BitScanReverse64(&r, x);
#else
    // Scan the high 32 bits.
    if (_BitScanReverse(&r, static_cast<uint32_t>(x >> 32)))
        return 63 - (r + 32);

    // Scan the low 32 bits.
    _BitScanReverse(&r, static_cast<uint32_t>(x & 0xFFFFFFFF));
#endif // _WIN64

    return 63 - r;
#elif (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
    // __builtin_clzll wrapper
    return static_cast<uint32_t>(__builtin_clzll(x));
#else
    // naive version
    uint32_t r = 0;
    while (!(x & (static_cast<uint64_t>(1) << 63))) {
        x <<= 1;
        ++r;
    }

    return r;
#endif // _MSC_VER
}

#define RAPIDJSON_CLZLL RAPIDJSON_NAMESPACE::internal::clzll

} // namespace internal
RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_CLZLL_H_
