From 84b8a220091e64bb1dd6c66fa49edac673df4ddb Mon Sep 17 00:00:00 2001
From: Stanislaw Halik <sthalik@misaki.pl>
Date: Fri, 12 Jan 2024 21:51:38 +0100
Subject: serialize/packbits: wip

---
 serialize/packbits.cpp | 55 ++++++++++++++++++++++++++++
 serialize/packbits.hpp | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 153 insertions(+)
 create mode 100644 serialize/packbits.cpp
 create mode 100644 serialize/packbits.hpp

diff --git a/serialize/packbits.cpp b/serialize/packbits.cpp
new file mode 100644
index 00000000..81c6c172
--- /dev/null
+++ b/serialize/packbits.cpp
@@ -0,0 +1,55 @@
+#include "packbits.hpp"
+
+namespace floormat {
+
+using namespace floormat::detail_Pack;
+
+namespace {
+
+constexpr bool test1()
+{
+    using S1 = Storage<uint8_t, 8>;
+    S1 st1{0b10111011};
+    fm_assert(st1.value == 0b10111011);
+
+    fm_assert(st1.get<3>() == 0b011);
+    using S2 = typename S1::next<3>;
+    S2 st2{st1.advance<3>()};
+    static_assert(std::is_same_v<S2, Storage<uint8_t, 5>>);
+    fm_assert(st2.value == 0b10111);
+
+    return true;
+}
+static_assert(test1());
+
+namespace test2 {
+template<size_t Val> using ibits = Bits_<uint16_t, Val>;
+using foo1 = ibits<2>;
+using foo2 = ibits<10>;
+using foo3 = ibits<4>;
+using bar1 = check_size_overflow<uint16_t, 0, foo1, foo2>;
+static_assert(bar1::result);
+static_assert(bar1::size == 12);
+
+using bar2 = check_size_overflow<uint16_t, 0, foo2>;
+static_assert(bar2::result);
+static_assert(bar2::size == 10);
+
+using bar3 = check_size_overflow<uint16_t, 0, foo1, foo2, foo3>;
+static_assert(bar3::result);
+static_assert(bar3::size == 16);
+
+using foo4 = ibits<1>;
+using bar4 = check_size_overflow<uint16_t, 0, foo1, foo2, foo3, foo4>;
+static_assert(!bar4::result);
+static_assert(bar4::size == 17);
+
+using foo5 = ibits<20>;
+using bar5 = check_size_overflow<uint16_t, 0, foo1, foo2, foo3, foo4, foo5>;
+static_assert(!bar5::result);
+static_assert(bar5::size == 37);
+} // namespace test2
+
+} // namespace
+
+} // namespace floormat
diff --git a/serialize/packbits.hpp b/serialize/packbits.hpp
new file mode 100644
index 00000000..6e388846
--- /dev/null
+++ b/serialize/packbits.hpp
@@ -0,0 +1,98 @@
+#pragma once
+#include "compat/assert.hpp"
+#include <type_traits>
+#include <concepts>
+
+namespace floormat::Pack {
+template<std::unsigned_integral T, uint8_t N> struct Bits_;
+} // namespace floormat::Pack
+
+namespace floormat::detail_Pack {
+
+using namespace floormat::Pack;
+template<std::unsigned_integral T, size_t Sum, typename... Xs> struct check_size_overflow;
+
+template<std::unsigned_integral T, std::unsigned_integral U, size_t Sum, uint8_t N, typename... Xs>
+struct check_size_overflow<T, Sum, Bits_<U, N>, Xs...>
+{
+    static_assert(std::is_same_v<T, U>);
+    static constexpr auto acc = Sum + size_t{N};
+    using next_check = check_size_overflow<T, acc, Xs...>;
+    static constexpr auto size = next_check::size;
+    static constexpr bool result = next_check::result;
+};
+
+template<std::unsigned_integral T, size_t Sum>
+struct check_size_overflow<T, Sum>
+{
+    static constexpr size_t size = Sum;
+    static constexpr bool result = Sum <= sizeof(T)*8;
+};
+
+template<std::unsigned_integral T, size_t Capacity>
+struct Storage
+{
+    static_assert(Capacity <= sizeof(T)*8);
+    T value;
+
+    template<size_t N>
+    constexpr T get()
+    {
+        static_assert(N <= sizeof(T)*8);
+        static_assert(N <= Capacity);
+        return T(value & (T(1) << N) - T(1));
+    }
+
+    template<size_t N>
+    constexpr T advance()
+    {
+        static_assert(N <= sizeof(T)*8);
+        static_assert(N <= Capacity);
+        return T(value >> N);
+    }
+
+    template<size_t N> [[maybe_unused]] constexpr bool check_zero() = delete;
+
+    template<size_t N>
+    using next = Storage<T, Capacity - N>;
+};
+
+template<std::unsigned_integral T>
+struct Storage<T, 0>
+{
+    T value;
+
+    template<size_t N> [[maybe_unused]] constexpr T get() = delete;
+    template<size_t N> [[maybe_unused]] constexpr T advance() = delete;
+
+    template<size_t N> constexpr inline bool check_zero()
+    {
+        fm_assert(value == T(0));
+        return true;
+    }
+
+    template<size_t N> struct next
+    {
+        static_assert(!std::is_same_v<T, void>, "reading past the end");
+        static_assert( std::is_same_v<T, void>, "can't happen!");
+    };
+};
+
+} // namespace floormat::detail_Pack
+
+namespace floormat::Pack {
+
+template<std::unsigned_integral T, uint8_t N>
+struct Bits_ final
+{
+    static_assert(std::is_fundamental_v<T>);
+    static_assert(N > 0);
+    static_assert(N < sizeof(T)*8);
+
+    using type = T;
+    static constexpr auto bits = N;
+};
+
+
+
+} // namespace floormat::Pack
-- 
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