diff --git a/Source/Core/InputCommon/ControllerInterface/MappingCommon.cpp b/Source/Core/InputCommon/ControllerInterface/MappingCommon.cpp
@@ -0,0 +1,149 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "InputCommon/ControllerInterface/MappingCommon.h"
+
+#include <algorithm>
+#include <chrono>
+#include <string>
+#include <vector>
+
+#include <fmt/format.h>
+
+#include "Common/StringUtil.h"
+#include "InputCommon/ControllerInterface/CoreDevice.h"
+
+namespace ciface::MappingCommon
+{
+// Pressing inputs at the same time will result in the & operator vs a hotkey expression.
+constexpr auto HOTKEY_VS_CONJUNCION_THRESHOLD = std::chrono::milliseconds(50);
+
+// Some devices (e.g. DS4) provide an analog and digital input for the trigger.
+// We prefer just the analog input for simultaneous digital+analog input detections.
+constexpr auto SPURIOUS_TRIGGER_COMBO_THRESHOLD = std::chrono::milliseconds(150);
+
+std::string GetExpressionForControl(const std::string& control_name,
+                                    const ciface::Core::DeviceQualifier& control_device,
+                                    const ciface::Core::DeviceQualifier& default_device,
+                                    Quote quote)
+{
+  std::string expr;
+
+  // non-default device
+  if (control_device != default_device)
+  {
+    expr += control_device.ToString();
+    expr += ':';
+  }
+
+  // append the control name
+  expr += control_name;
+
+  if (quote == Quote::On)
+  {
+    // If our expression contains any non-alpha characters
+    // we should quote it
+    if (!std::all_of(expr.begin(), expr.end(), IsAlpha))
+      expr = fmt::format("`{}`", expr);
+  }
+
+  return expr;
+}
+
+std::string
+BuildExpression(const std::vector<ciface::Core::DeviceContainer::InputDetection>& detections,
+                const ciface::Core::DeviceQualifier& default_device, Quote quote)
+{
+  std::vector<const ciface::Core::DeviceContainer::InputDetection*> pressed_inputs;
+
+  std::vector<std::string> alternations;
+
+  const auto get_control_expression = [&](auto& detection) {
+    // Return the parent-most name if there is one for better hotkey strings.
+    // Detection of L/R_Ctrl will be changed to just Ctrl.
+    // Users can manually map L_Ctrl if they so desire.
+    const auto input = (quote == Quote::On) ?
+                           detection.device->GetParentMostInput(detection.input) :
+                           detection.input;
+
+    ciface::Core::DeviceQualifier device_qualifier;
+    device_qualifier.FromDevice(detection.device.get());
+
+    return MappingCommon::GetExpressionForControl(input->GetName(), device_qualifier,
+                                                  default_device, quote);
+  };
+
+  bool new_alternation = false;
+
+  const auto handle_press = [&](auto& detection) {
+    pressed_inputs.emplace_back(&detection);
+    new_alternation = true;
+  };
+
+  const auto handle_release = [&]() {
+    if (!new_alternation)
+      return;
+
+    new_alternation = false;
+
+    std::vector<std::string> alternation;
+    for (auto* input : pressed_inputs)
+      alternation.push_back(get_control_expression(*input));
+
+    const bool is_hotkey = pressed_inputs.size() >= 2 &&
+                           (pressed_inputs[1]->press_time - pressed_inputs[0]->press_time) >
+                               HOTKEY_VS_CONJUNCION_THRESHOLD;
+
+    if (is_hotkey)
+    {
+      alternations.push_back(fmt::format("@({})", JoinStrings(alternation, "+")));
+    }
+    else
+    {
+      std::sort(alternation.begin(), alternation.end());
+      alternations.push_back(JoinStrings(alternation, "&"));
+    }
+  };
+
+  for (auto& detection : detections)
+  {
+    // Remove since released inputs.
+    for (auto it = pressed_inputs.begin(); it != pressed_inputs.end();)
+    {
+      if (!((*it)->release_time > detection.press_time))
+      {
+        handle_release();
+        it = pressed_inputs.erase(it);
+      }
+      else
+        ++it;
+    }
+
+    handle_press(detection);
+  }
+
+  handle_release();
+
+  // Remove duplicates
+  std::sort(alternations.begin(), alternations.end());
+  alternations.erase(std::unique(alternations.begin(), alternations.end()), alternations.end());
+
+  return JoinStrings(alternations, "|");
+}
+
+void RemoveSpuriousTriggerCombinations(
+    std::vector<ciface::Core::DeviceContainer::InputDetection>* detections)
+{
+  const auto is_spurious = [&](auto& detection) {
+    return std::any_of(detections->begin(), detections->end(), [&](auto& d) {
+      // This is a suprious digital detection if a "smooth" (analog) detection is temporally near.
+      return &d != &detection && d.smoothness > 1 &&
+             abs(d.press_time - detection.press_time) < SPURIOUS_TRIGGER_COMBO_THRESHOLD;
+    });
+  };
+
+  detections->erase(std::remove_if(detections->begin(), detections->end(), is_spurious),
+                    detections->end());
+}
+
+}  // namespace ciface::MappingCommon
diff --git a/Source/Core/InputCommon/ControllerInterface/MappingCommon.h b/Source/Core/InputCommon/ControllerInterface/MappingCommon.h
@@ -0,0 +1,29 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "InputCommon/ControllerInterface/CoreDevice.h"
+
+namespace ciface::MappingCommon
+{
+enum class Quote
+{
+  On,
+  Off
+};
+
+std::string GetExpressionForControl(const std::string& control_name,
+                                    const ciface::Core::DeviceQualifier& control_device,
+                                    const ciface::Core::DeviceQualifier& default_device,
+                                    Quote quote = Quote::On);
+
+std::string BuildExpression(const std::vector<ciface::Core::DeviceContainer::InputDetection>&,
+                            const ciface::Core::DeviceQualifier& default_device, Quote quote);
+
+void RemoveSpuriousTriggerCombinations(std::vector<ciface::Core::DeviceContainer::InputDetection>*);
+
+}  // namespace ciface::MappingCommon