Start developing paging

1 files changed, 53 insertions, 0 deletions

diff --git a/arch/x86_64/src/memory/paging.cpp b/arch/x86_64/src/memory/paging.cpp
new file mode 100644
index 0000000..555357c
--- /dev/null
+++ b/arch/x86_64/src/memory/paging.cpp
@@ -0,0 +1,53 @@
+#include "arch/memory/paging.hpp"
+
+namespace teachos::arch::memory
+{
+  auto entry::is_unused() const -> bool { return flags == 0U; }
+
+  auto entry::set_unused() -> void { flags = 0U; }
+
+  auto entry::present() const -> bool { return is_bit_set(0U); }
+
+  auto entry::writable() const -> bool { return is_bit_set(1U); }
+
+  auto entry::user_accessible() const -> bool { return is_bit_set(2U); }
+
+  auto entry::write_through_caching() const -> bool { return is_bit_set(3U); }
+
+  auto entry::disabled_caching() const -> bool { return is_bit_set(4U); }
+
+  auto entry::is_accessing() const -> bool { return is_bit_set(5U); }
+
+  auto entry::is_diry() const -> bool { return is_bit_set(6U); }
+
+  auto entry::is_huge_page() const -> bool { return is_bit_set(7U); }
+
+  auto entry::is_global() const -> bool { return is_bit_set(8U); }
+
+  auto entry::executing_code_forbidden() const -> bool { return is_bit_set(63U); }
+
+  auto entry::calculate_pointed_to_frame() const -> std::optional<physical_frame>
+  {
+    if (present())
+    {
+      auto physical_address = calculate_physical_address();
+      return physical_frame::containing_address(physical_address);
+    }
+    return std::nullopt;
+  }
+
+  auto entry::calculate_physical_address() const -> std::size_t
+  {
+    constexpr std::size_t start_bit = 12U;
+    constexpr std::size_t end_bit = 51U;
+    size_t value = 0U;
+
+    for (auto i = start_bit; i < end_bit; i++)
+    {
+      value |= (flags[i] ? (1 << (i - start_bit)) : 0);
+    }
+    return value;
+  }
+
+  auto entry::is_bit_set(uint8_t index) const -> bool { return flags[index] == 1U; }
+}  // namespace teachos::arch::memory