service/hid: Create ring LIFO

1 files changed, 54 insertions, 0 deletions

diff --git a/src/core/hle/service/hid/ring_lifo.h b/src/core/hle/service/hid/ring_lifo.h
new file mode 100644
index 000000000..1cc2a194f
--- /dev/null
+++ b/src/core/hle/service/hid/ring_lifo.h
@@ -0,0 +1,54 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included
+
+#pragma once
+
+#include "common/common_types.h"
+#include "common/swap.h"
+
+namespace Service::HID {
+constexpr std::size_t max_entry_size = 17;
+
+template <typename State>
+struct AtomicStorage {
+    s64_le sampling_number;
+    State state;
+};
+
+template <typename State>
+struct Lifo {
+    s64_le timestamp{};
+    s64_le total_entry_count = max_entry_size;
+    s64_le last_entry_index{};
+    s64_le entry_count{};
+    std::array<AtomicStorage<State>, max_entry_size> entries{};
+
+    const AtomicStorage<State>& ReadCurrentEntry() const {
+        return entries[last_entry_index];
+    }
+
+    const AtomicStorage<State>& ReadPreviousEntry() const {
+        return entries[GetPreviuousEntryIndex()];
+    }
+
+    std::size_t GetPreviuousEntryIndex() const {
+        return (last_entry_index + total_entry_count - 1) % total_entry_count;
+    }
+
+    std::size_t GetNextEntryIndex() const {
+        return (last_entry_index + 1) % total_entry_count;
+    }
+
+    void WriteNextEntry(const State& new_state) {
+        if (entry_count < total_entry_count - 1) {
+            entry_count++;
+        }
+        last_entry_index = GetNextEntryIndex();
+        const auto& previous_entry = ReadPreviousEntry();
+        entries[last_entry_index].sampling_number = previous_entry.sampling_number + 1;
+        entries[last_entry_index].state = new_state;
+    }
+};
+
+} // namespace Service::HID