diff --git a/libs/input/InputVerifier.cpp b/libs/input/InputVerifier.cpp
new file mode 100644
index 0000000..eb75804
--- /dev/null
+++ b/libs/input/InputVerifier.cpp
@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "InputVerifier"
+
+#include <android-base/logging.h>
+#include <input/InputVerifier.h>
+
+namespace android {
+
+/**
+ * Log all of the movements that are sent to this verifier. Helps to identify the streams that lead
+ * to inconsistent events.
+ * Enable this via "adb shell setprop log.tag.InputVerifierLogEvents DEBUG"
+ */
+static bool logEvents() {
+    return __android_log_is_loggable(ANDROID_LOG_DEBUG, LOG_TAG "LogEvents", ANDROID_LOG_INFO);
+}
+
+// --- InputVerifier ---
+
+InputVerifier::InputVerifier(const std::string& name) : mName(name){};
+
+void InputVerifier::processMovement(int32_t deviceId, int32_t action, uint32_t pointerCount,
+                                    const PointerProperties* pointerProperties,
+                                    const PointerCoords* pointerCoords, int32_t flags) {
+    if (logEvents()) {
+        LOG(ERROR) << "Processing " << MotionEvent::actionToString(action) << " for device "
+                   << deviceId << " (" << pointerCount << " pointer"
+                   << (pointerCount == 1 ? "" : "s") << ") on " << mName;
+    }
+
+    switch (MotionEvent::getActionMasked(action)) {
+        case AMOTION_EVENT_ACTION_DOWN: {
+            auto [it, inserted] = mTouchingPointerIdsByDevice.insert({deviceId, {}});
+            if (!inserted) {
+                LOG(FATAL) << "Got ACTION_DOWN, but already have touching pointers " << it->second
+                           << " for device " << deviceId << " on " << mName;
+            }
+            it->second.set(pointerProperties[0].id);
+            break;
+        }
+        case AMOTION_EVENT_ACTION_POINTER_DOWN: {
+            auto it = mTouchingPointerIdsByDevice.find(deviceId);
+            if (it == mTouchingPointerIdsByDevice.end()) {
+                LOG(FATAL) << "Got POINTER_DOWN, but no touching pointers for device " << deviceId
+                           << " on " << mName;
+            }
+            it->second.set(pointerProperties[MotionEvent::getActionIndex(action)].id);
+            break;
+        }
+        case AMOTION_EVENT_ACTION_MOVE: {
+            ensureTouchingPointersMatch(deviceId, pointerCount, pointerProperties, "MOVE");
+            break;
+        }
+        case AMOTION_EVENT_ACTION_POINTER_UP: {
+            auto it = mTouchingPointerIdsByDevice.find(deviceId);
+            if (it == mTouchingPointerIdsByDevice.end()) {
+                LOG(FATAL) << "Got POINTER_UP, but no touching pointers for device " << deviceId
+                           << " on " << mName;
+            }
+            it->second.reset(pointerProperties[MotionEvent::getActionIndex(action)].id);
+            break;
+        }
+        case AMOTION_EVENT_ACTION_UP: {
+            auto it = mTouchingPointerIdsByDevice.find(deviceId);
+            if (it == mTouchingPointerIdsByDevice.end()) {
+                LOG(FATAL) << "Got ACTION_UP, but no record for deviceId " << deviceId << " on "
+                           << mName;
+            }
+            const auto& [_, touchingPointerIds] = *it;
+            if (touchingPointerIds.count() != 1) {
+                LOG(FATAL) << "Got ACTION_UP, but we have pointers: " << touchingPointerIds
+                           << " for deviceId " << deviceId << " on " << mName;
+            }
+            const int32_t pointerId = pointerProperties[0].id;
+            if (!touchingPointerIds.test(pointerId)) {
+                LOG(FATAL) << "Got ACTION_UP, but pointerId " << pointerId
+                           << " is not touching. Touching pointers: " << touchingPointerIds
+                           << " for deviceId " << deviceId << " on " << mName;
+            }
+            mTouchingPointerIdsByDevice.erase(it);
+            break;
+        }
+        case AMOTION_EVENT_ACTION_CANCEL: {
+            if ((flags & AMOTION_EVENT_FLAG_CANCELED) != AMOTION_EVENT_FLAG_CANCELED) {
+                LOG(FATAL) << "For ACTION_CANCEL, must set FLAG_CANCELED";
+            }
+            ensureTouchingPointersMatch(deviceId, pointerCount, pointerProperties, "CANCEL");
+            mTouchingPointerIdsByDevice.erase(deviceId);
+            break;
+        }
+    }
+}
+
+void InputVerifier::ensureTouchingPointersMatch(int32_t deviceId, uint32_t pointerCount,
+                                                const PointerProperties* pointerProperties,
+                                                const char* action) const {
+    auto it = mTouchingPointerIdsByDevice.find(deviceId);
+    if (it == mTouchingPointerIdsByDevice.end()) {
+        LOG(FATAL) << "Got " << action << ", but no touching pointers for device " << deviceId
+                   << " on " << mName;
+    }
+    const auto& [_, touchingPointerIds] = *it;
+    for (size_t i = 0; i < pointerCount; i++) {
+        const int32_t pointerId = pointerProperties[i].id;
+        if (!touchingPointerIds.test(pointerId)) {
+            LOG(FATAL) << "Got " << action << " for pointerId " << pointerId
+                       << " but the touching pointers are " << touchingPointerIds << " on "
+                       << mName;
+        }
+    }
+};
+
+} // namespace android