6 files changed, 57 insertions, 18 deletions
diff --git a/serialize/packbits-impl.cpp b/serialize/packbits-impl.cpp
new file mode 100644
index 00000000..b7a4eefc
--- /dev/null
+++ b/serialize/packbits-impl.cpp
@@ -0,0 +1,11 @@
+#include "packbits-impl.hpp"
+#include "compat/exception.hpp"
+
+namespace floormat::Pack_impl {
+
+void throw_on_read_nonzero() noexcept(false)
+{
+    throw std::runtime_error{"extra bits in pack_read()"};
+}
+
+} // namespace floormat::Pack_impl
diff --git a/serialize/packbits-impl.hpp b/serialize/packbits-impl.hpp
new file mode 100644
index 00000000..3e57ea75
--- /dev/null
+++ b/serialize/packbits-impl.hpp
@@ -0,0 +1,13 @@
+#pragma once
+
+namespace floormat::Pack_impl {
+
+[[noreturn]] void throw_on_read_nonzero() noexcept(false);
+[[noreturn]] void throw_on_write_input_bit_overflow() noexcept(false);
+
+template<size_t... Ns> struct expand_sum;
+template<size_t N, size_t... Ns> struct expand_sum<N, Ns...> { static constexpr size_t value = N + expand_sum<Ns...>::value; };
+template<> struct expand_sum<> { static constexpr size_t value = 0; };
+template<size_t... Ns> constexpr inline size_t sum = expand_sum<Ns...>::value;
+
+} // namespace floormat::Pack_impl
diff --git a/serialize/packbits-read.cpp b/serialize/packbits-read.cpp
index 6b4a13d4..9980ca63 100644
--- a/serialize/packbits-read.cpp
+++ b/serialize/packbits-read.cpp
@@ -1,12 +1,29 @@
 #include "packbits-read.hpp"
 #include "compat/assert.hpp"
+#include "compat/exception.hpp"
+
+namespace floormat::Pack_impl {
+
+void throw_on_read_nonzero() noexcept(false)
+{
+    throw std::runtime_error{"extra bits in pack_read()"};
+}
+
+} // namespace floormat::Pack_impl
 
 namespace floormat {
 
-using namespace floormat::Pack;
+using namespace floormat::Pack_impl;
 
 namespace {
 
+static_assert(sum<1, 2, 3, 4, 5> == 6*(6-1)/2);
+static_assert(sum<5, 10, 15> == 30);
+
+using u32 = uint32_t;
+using u16 = uint16_t;
+using u8 = uint8_t;
+
 template<std::unsigned_integral T, size_t N> constexpr inline T lowbits = N == sizeof(T)*8 ? (T)-1 : (T{1} << N)-T{1};
 
 static_assert(!input<uint32_t, 3>{65535}.check_zero());
diff --git a/serialize/packbits-read.hpp b/serialize/packbits-read.hpp
index 6f5dd883..2ea50848 100644
--- a/serialize/packbits-read.hpp
+++ b/serialize/packbits-read.hpp
@@ -1,11 +1,13 @@
 #pragma once
+#include "packbits-impl.hpp"
+#include "compat/reverse-index-sequence.hpp"
 #include <type_traits>
 #include <concepts>
 #include <tuple>
 #include <utility>
 #include "compat/assert.hpp"
 
-namespace floormat::Pack {
+namespace floormat::Pack_impl {
 
 template<std::unsigned_integral T, size_t N>
 struct input_bits final
@@ -105,7 +107,8 @@ constexpr void read_(Place& p, input<T, Left> st, std::index_sequence<I, Is...>,
 template<std::unsigned_integral T, typename Place, size_t Left>
 constexpr void read_(Place&, input<T, Left> st, std::index_sequence<>, empty_pack_tuple<>)
 {
-    fm_assert(st.check_zero());
+    if (!st.check_zero()) [[unlikely]]
+        throw_on_read_nonzero();
 }
 
 template<std::unsigned_integral T, typename Place, size_t Left, size_t... Is, typename... Sizes>
@@ -114,17 +117,10 @@ constexpr void read_(Place&, input<T, Left>, std::index_sequence<Is...>, empty_p
 
 template<std::unsigned_integral T, size_t... Ns> using make_pack = empty_pack_tuple<input_bits<T, Ns>...>;
 
-} // namespace floormat::Pack
+} // namespace floormat::Pack_impl
 
 namespace floormat {
 
-template<std::unsigned_integral T, size_t... Sizes>
-constexpr T pack_write(const std::tuple<Pack::output_field<T, Sizes>...>& tuple)
-{
-    constexpr size_t nbits = sizeof(T)*8;
-    return Pack::write_(tuple, Pack::output<T, nbits, nbits>{T{0}}, make_reverse_index_sequence<sizeof...(Sizes)>{});
-}
 
-constexpr uint8_t pack_write(const std::tuple<>&) = delete;
 
 } // namespace floormat
diff --git a/serialize/packbits-write.cpp b/serialize/packbits-write.cpp
index 5db0fa1b..f485a72e 100644
--- a/serialize/packbits-write.cpp
+++ b/serialize/packbits-write.cpp
@@ -4,7 +4,7 @@ namespace floormat {
 
 namespace {
 
-using namespace floormat::Pack;
+using namespace floormat::Pack_impl;
 
 using u32 = uint32_t;
 using u16 = uint16_t;
diff --git a/serialize/packbits-write.hpp b/serialize/packbits-write.hpp
index 5a8eae52..ca18cfbb 100644
--- a/serialize/packbits-write.hpp
+++ b/serialize/packbits-write.hpp
@@ -1,12 +1,12 @@
 #pragma once
-#include "compat/assert.hpp"
+#include "packbits-impl.hpp"
 #include "compat/reverse-index-sequence.hpp"
 #include <type_traits>
 #include <bit>
 #include <concepts>
 #include <tuple>
 
-namespace floormat::Pack {
+namespace floormat::Pack_impl {
 
 template<std::unsigned_integral T, size_t CAPACITY, size_t LEFT>
 struct output
@@ -42,7 +42,9 @@ constexpr CORRADE_ALWAYS_INLINE T write_(const Tuple& tuple, output<T, Capacity,
     static_assert(N <= Left);
 
     T x = std::get<I>(tuple).value;
-    fm_assert((size_t)std::bit_width(x) <= N);
+
+    if (!((size_t)std::bit_width(x) <= N)) [[unlikely]]
+        throw_on_write_input_bit_overflow();
     T value = T(T(st.value << N) | x);
     return write_(tuple, output<T, Capacity, Left - N>{value}, std::index_sequence<Is...>{});
 }
@@ -53,15 +55,15 @@ constexpr CORRADE_ALWAYS_INLINE T write_(const Tuple&, output<T, Capacity, Left>
     return st.value;
 }
 
-} // namespace floormat::Pack
+} // namespace floormat::Pack_impl
 
 namespace floormat {
 
 template<std::unsigned_integral T, size_t... Sizes>
-constexpr T pack_write(const std::tuple<Pack::output_field<T, Sizes>...>& tuple)
+constexpr T pack_write(const std::tuple<Pack_impl::output_field<T, Sizes>...>& tuple)
 {
     constexpr size_t nbits = sizeof(T)*8;
-    return Pack::write_(tuple, Pack::output<T, nbits, nbits>{T{0}}, make_reverse_index_sequence<sizeof...(Sizes)>{});
+    return Pack_impl::write_(tuple, Pack_impl::output<T, nbits, nbits>{T{0}}, make_reverse_index_sequence<sizeof...(Sizes)>{});
 }
 
 constexpr uint8_t pack_write(const std::tuple<>&) = delete;