Add mozc dial version.

Co-authored-by: Takashi Toyoshima <toyoshim@google.com>
Co-authored-by: Shun Ikejima <ikejima@google.com>

mozc-dial/firmware/common/dial_controller.cc

@@ -0,0 +1,45 @@
+// Copyright 2025 Google Inc.
+// Use of this source code is governed by an Apache License that can be found
+// in the LICENSE file.
+
+#include "dial_controller.h"
+
+#include <algorithm>
+
+namespace {
+
+constexpr uint8_t kBasePosition = 0;
+
+uint8_t ConvertGrayToBinary(uint8_t gray) {
+  uint8_t binary = gray;
+  uint8_t mask = gray >> 1;
+
+  while (mask) {
+    binary ^= mask;
+    mask >>= 1;
+  }
+  return binary;
+}
+
+}  // namespace
+
+DialController::DialController() {}
+
+void DialController::Update(uint8_t sensor_gray_code) {
+  position_ = ConvertGrayToBinary(sensor_gray_code);
+  max_position_ = std::max(max_position_, position_);
+  if (position_ == kBasePosition && max_position_ != kBasePosition) {
+    decided_position_ = max_position_;
+    max_position_ = kBasePosition;
+  }
+}
+
+bool DialController::IsBasePosition() const {
+  return position_ == kBasePosition;
+}
+
+std::optional<uint8_t> DialController::PopDecidedPosition() {
+  auto result = decided_position_;
+  decided_position_ = std::nullopt;
+  return result;
+}