diff --git a/include/bit.h b/include/bit.h
index 992ecbb..d50ec7d 100644
--- a/include/bit.h
+++ b/include/bit.h
@@ -7,8 +7,6 @@
 
 namespace dark {
 
-static constexpr std::size_t kMaxLength = std::numeric_limits<max_size_t>::digits;
-
 template <std::size_t _Nm>
 struct Bit {
   private:
@@ -31,10 +29,10 @@ struct Bit {
     requires ((_Tp::_Bit_Len + ...) == _Nm)
     constexpr Bit(const _Tp &...args);
 
-    template <concepts::bit_match <Bit> _Tp>
+    template <concepts::bit_convertible <_Nm> _Tp>
     constexpr Bit &operator=(const _Tp &val);
 
-    template <std::size_t _Hi, std::size_t _Lo = _Hi, concepts::bit_match <Bit> _Tp>
+    template <std::size_t _Hi, std::size_t _Lo = _Hi, concepts::bit_convertible <_Nm> _Tp>
     constexpr void set(const _Tp &val);
 
     template <std::size_t _Hi, std::size_t _Lo = _Hi>
diff --git a/include/bit_impl.h b/include/bit_impl.h
index a62f15d..e67ec17 100644
--- a/include/bit_impl.h
+++ b/include/bit_impl.h
@@ -42,7 +42,7 @@ constexpr Bit<_Nm>::Bit(const _Tp &...args)
     : _M_data(int_concat<_Tp::_Bit_Len...>(static_cast<max_size_t>(args)...)) {}
 
 template <std::size_t _Nm>
-template <concepts::bit_match <Bit <_Nm>> _Tp>
+template <concepts::bit_convertible <_Nm> _Tp>
 constexpr Bit<_Nm> &Bit<_Nm>::operator=(const _Tp &val) {
     this->_M_data = static_cast<max_size_t>(val);
     return *this;
@@ -56,17 +56,13 @@ constexpr void Bit<_Nm>::_M_range_check() {
 }
 
 template <std::size_t _Nm>
-template <std::size_t _Hi, std::size_t _Lo, concepts::bit_match <Bit<_Nm>> _Tp>
+template <std::size_t _Hi, std::size_t _Lo, concepts::bit_convertible <_Nm> _Tp>
 constexpr void Bit<_Nm>::set(const _Tp &val) {
     this->_M_range_check<_Hi, _Lo>();
     auto data = static_cast<max_size_t>(val);
     constexpr auto _Length = _Hi - _Lo + 1;
-    if constexpr (_Length == kMaxLength) {
-        this->_M_data = data;
-    } else {
-        auto mask = ((1 << _Length) - 1) << _Lo;
-        this->_M_data = (this->_M_data & ~mask) | ((data << _Lo) & mask);
-    }
+    auto mask = make_mask<_Length> << _Lo;
+    this->_M_data = (this->_M_data & ~mask) | ((data << _Lo) & mask);
 }
 
 template <std::size_t _Nm>
@@ -82,11 +78,7 @@ template <std::size_t _Len>
 constexpr auto Bit<_Nm>::slice(std::size_t pos) const -> Bit <_Len> {
     static_assert(_Len <= _Nm, "Bit::slice: _Len should be no greater than _Nm");
     debug::assert(pos <= _Nm - _Len, "Bit::slice: pos should be less than _Nm - _Len");
-    if constexpr (_Len == kMaxLength) {
-        return *this;
-    } else {
-        return Bit<_Len>(this->_M_data >> pos);
-    }
+    return Bit<_Len>(this->_M_data >> pos);
 }
 
 
diff --git a/include/concept.h b/include/concept.h
index 6d47846..905e98c 100644
--- a/include/concept.h
+++ b/include/concept.h
@@ -7,6 +7,14 @@ namespace dark {
 using max_size_t = std::uint32_t;
 using max_ssize_t = std::int32_t;
 
+static constexpr std::size_t kMaxLength = std::numeric_limits<max_size_t>::digits;
+
+template <std::size_t _Len>
+consteval max_size_t make_mask() {
+    static_assert(_Len <= kMaxLength, "Mask length out of range");
+    return _Len == kMaxLength ? ~max_size_t(0) : (max_size_t(1) << _Len) - 1;
+}
+
 } // namespace dark
 
 namespace dark::concepts {
@@ -38,4 +46,8 @@ concept bit_match =
     (bit_type <_Lhs> && bit_type <_Rhs> && _Lhs::_Bit_Len == _Rhs::_Bit_Len)
 ||  (int_type <_Lhs> || int_type <_Rhs>);
 
+template <typename _Tp, std::size_t _Len>
+concept bit_convertible =
+    (bit_type <_Tp> && _Tp::_Bit_Len == _Len) || int_type <_Tp>;
+
 } // namespace dark::concepts