kernel/memory: implement basic bitmap allocator

1 files changed, 100 insertions, 0 deletions

diff --git a/kernel/src/memory/bitmap_allocator.cpp b/kernel/src/memory/bitmap_allocator.cpp
new file mode 100644
index 0000000..c010f77
--- /dev/null
+++ b/kernel/src/memory/bitmap_allocator.cpp
@@ -0,0 +1,100 @@
+#include "kernel/memory/bitmap_allocator.hpp"
+
+#include "kapi/memory.hpp"
+
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <optional>
+#include <span>
+#include <utility>
+
+namespace kernel::memory
+{
+
+  bitmap_frame_allocator::bitmap_frame_allocator(std::span<std::uint64_t> storage, std::size_t frame_count) noexcept
+      : m_bitmap{storage}
+      , m_frame_count{frame_count}
+      , m_last_index{}
+  {
+    std::ranges::fill(m_bitmap, ~0uz);
+  }
+
+  auto bitmap_frame_allocator::allocate_many(std::size_t count) noexcept
+      -> std::optional<std::pair<kapi::memory::frame, std::size_t>>
+  {
+    if (count == 0)
+    {
+      return std::nullopt;
+    }
+
+    auto free_count = 0uz;
+    auto first_free = 0uz;
+
+    for (auto i = 0uz; i < m_frame_count; ++i)
+    {
+      auto const current = (m_last_index + i) % m_frame_count;
+      if (!test(current))
+      {
+        if (free_count == 0)
+        {
+          first_free = current;
+        }
+
+        ++free_count;
+
+        if (free_count == count)
+        {
+          for (auto j = 0uz; j < count; ++j)
+          {
+            set(first_free + j);
+          }
+          m_last_index = first_free + count;
+          return std::make_pair(kapi::memory::frame{first_free}, count);
+        }
+      }
+      else
+      {
+        free_count = 0;
+      }
+    }
+
+    return std::nullopt;
+  }
+
+  auto bitmap_frame_allocator::release_many(std::pair<kapi::memory::frame, std::size_t> frame_set) -> void
+  {
+    auto const [start, count] = frame_set;
+    for (auto i = 0uz; i < count; ++i)
+    {
+      clear(start.number() + i);
+    }
+  }
+
+  auto bitmap_frame_allocator::mark_used(kapi::memory::frame frame) -> void
+  {
+    set(frame.number());
+  }
+
+  auto bitmap_frame_allocator::test(std::size_t index) const noexcept -> bool
+  {
+    auto entry_entry = index / 64;
+    auto entry_offset = index % 64;
+    return (m_bitmap[entry_entry] & (1uz << entry_offset));
+  }
+
+  auto bitmap_frame_allocator::set(std::size_t index) noexcept -> void
+  {
+    auto entry_entry = index / 64;
+    auto entry_offset = index % 64;
+    m_bitmap[entry_entry] |= (1uz << entry_offset);
+  }
+
+  auto bitmap_frame_allocator::clear(std::size_t index) noexcept -> void
+  {
+    auto entry_entry = index / 64;
+    auto entry_offset = index % 64;
+    m_bitmap[entry_entry] &= ~(1uz << entry_offset);
+  }
+
+}  // namespace kernel::memory
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