cts/helpers/SensorCtsHelper.java

/*
 * Copyright (C) 2013 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.
 */
package android.hardware.cts.helpers;

import android.hardware.Sensor;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.TimeUnit;

/**
 * Set of static helper methods for CTS tests.
 */
//TODO: Refactor this class into several more well defined helper classes, look at StatisticsUtils
public class SensorCtsHelper {

    private static final long NANOS_PER_MILLI = 1000000;

    /**
     * Private constructor for static class.
     */
    private SensorCtsHelper() {}

    /**
     * Get percentiles using nearest rank algorithm.
     *
     * @param percentiles List of percentiles interested. Its range is 0 to 1, instead of in %.
     *        The value will be internally bounded.
     *
     * @throws IllegalArgumentException if the collection or percentiles is null or empty
     */
    public static <TValue extends Comparable<? super TValue>> List<TValue> getPercentileValue(
            Collection<TValue> collection, float[] percentiles) {
        validateCollection(collection);
        if(percentiles == null || percentiles.length == 0) {
            throw new IllegalStateException("percentiles cannot be null or empty");
        }

        List<TValue> arrayCopy = new ArrayList<TValue>(collection);
        Collections.sort(arrayCopy);

        List<TValue> percentileValues = new ArrayList<TValue>();
        for (float p : percentiles) {
            // zero-based array index
            int arrayIndex = (int) Math.round(arrayCopy.size() * p - .5f);
            // bound the index to avoid out of range error
            arrayIndex = Math.min(Math.max(arrayIndex, 0), arrayCopy.size() - 1);
            percentileValues.add(arrayCopy.get(arrayIndex));
        }
        return percentileValues;
    }

    /**
     * Calculate the mean of a collection.
     *
     * @throws IllegalArgumentException if the collection is null or empty
     */
    public static <TValue extends Number> double getMean(Collection<TValue> collection) {
        validateCollection(collection);

        double sum = 0.0;
        for(TValue value : collection) {
            sum += value.doubleValue();
        }
        return sum / collection.size();
    }

    /**
     * Calculate the bias-corrected sample variance of a collection.
     *
     * @throws IllegalArgumentException if the collection is null or empty
     */
    public static <TValue extends Number> double getVariance(Collection<TValue> collection) {
        validateCollection(collection);

        double mean = getMean(collection);
        ArrayList<Double> squaredDiffs = new ArrayList<Double>();
        for(TValue value : collection) {
            double difference = mean - value.doubleValue();
            squaredDiffs.add(Math.pow(difference, 2));
        }

        double sum = 0.0;
        for (Double value : squaredDiffs) {
            sum += value;
        }
        return sum / (squaredDiffs.size() - 1);
    }

    /**
     * @return The (measured) sampling rate of a collection of {@link TestSensorEvent}.
     */
    public static long getSamplingPeriodNs(List<TestSensorEvent> collection) {
        int collectionSize = collection.size();
        if (collectionSize < 2) {
            return 0;
        }
        TestSensorEvent firstEvent = collection.get(0);
        TestSensorEvent lastEvent = collection.get(collectionSize - 1);
        return (lastEvent.timestamp - firstEvent.timestamp) / (collectionSize - 1);
    }

    /**
     * Calculate the bias-corrected standard deviation of a collection.
     *
     * @throws IllegalArgumentException if the collection is null or empty
     */
    public static <TValue extends Number> double getStandardDeviation(
            Collection<TValue> collection) {
        return Math.sqrt(getVariance(collection));
    }

    /**
     * Convert a period to frequency in Hz.
     */
    public static <TValue extends Number> double getFrequency(TValue period, TimeUnit unit) {
        return 1000000000 / (TimeUnit.NANOSECONDS.convert(1, unit) * period.doubleValue());
    }

    /**
     * Convert a frequency in Hz into a period.
     */
    public static <TValue extends Number> double getPeriod(TValue frequency, TimeUnit unit) {
        return 1000000000 / (TimeUnit.NANOSECONDS.convert(1, unit) * frequency.doubleValue());
    }

    /**
     * If value lies outside the boundary limit, then return the nearer bound value.
     * Otherwise, return the value unchanged.
     */
    public static <TValue extends Number> double clamp(TValue val, TValue min, TValue max) {
        return Math.min(max.doubleValue(), Math.max(min.doubleValue(), val.doubleValue()));
    }

    /**
     * @return The magnitude (norm) represented by the given array of values.
     */
    public static double getMagnitude(float[] values) {
        float sumOfSquares = 0.0f;
        for (float value : values) {
            sumOfSquares += value * value;
        }
        double magnitude = Math.sqrt(sumOfSquares);
        return magnitude;
    }

    /**
     * Helper method to sleep for a given duration.
     */
    public static void sleep(long duration, TimeUnit timeUnit) throws InterruptedException {
        long durationNs = TimeUnit.NANOSECONDS.convert(duration, timeUnit);
        Thread.sleep(durationNs / NANOS_PER_MILLI, (int) (durationNs % NANOS_PER_MILLI));
    }

    /**
     * Format an assertion message.
     *
     * @param label the verification name
     * @param environment the environment of the test
     *
     * @return The formatted string
     */
    public static String formatAssertionMessage(String label, TestSensorEnvironment environment) {
        return formatAssertionMessage(label, environment, "Failed");
    }

    /**
     * Format an assertion message with a custom message.
     *
     * @param label the verification name
     * @param environment the environment of the test
     * @param format the additional format string
     * @param params the additional format params
     *
     * @return The formatted string
     */
    public static String formatAssertionMessage(
            String label,
            TestSensorEnvironment environment,
            String format,
            Object ... params) {
        return formatAssertionMessage(label, environment, String.format(format, params));
    }

    /**
     * Format an assertion message.
     *
     * @param label the verification name
     * @param environment the environment of the test
     * @param extras the additional information for the assertion
     *
     * @return The formatted string
     */
    public static String formatAssertionMessage(
            String label,
            TestSensorEnvironment environment,
            String extras) {
        return String.format(
                "%s | sensor='%s', samplingPeriod=%dus, maxReportLatency=%dus | %s",
                label,
                environment.getSensor().getName(),
                environment.getRequestedSamplingPeriodUs(),
                environment.getMaxReportLatencyUs(),
                extras);
    }

    /**
     * @return A {@link File} representing a root directory to store sensor tests data.
     */
    public static File getSensorTestDataDirectory() throws IOException {
        File dataDirectory = new File(System.getenv("EXTERNAL_STORAGE"), "sensorTests/");
        return createDirectoryStructure(dataDirectory);
    }

    /**
     * Creates the directory structure for the given sensor test data sub-directory.
     *
     * @param subdirectory The sub-directory's name.
     */
    public static File getSensorTestDataDirectory(String subdirectory) throws IOException {
        File subdirectoryFile = new File(getSensorTestDataDirectory(), subdirectory);
        return createDirectoryStructure(subdirectoryFile);
    }

    /**
     * Sanitizes a string so it can be used in file names.
     *
     * @param value The string to sanitize.
     * @return The sanitized string.
     *
     * @throws SensorTestPlatformException If the string cannot be sanitized.
     */
    public static String sanitizeStringForFileName(String value)
            throws SensorTestPlatformException {
        String sanitizedValue = value.replaceAll("[^a-zA-Z0-9_\\-]", "_");
        if (sanitizedValue.matches("_*")) {
            throw new SensorTestPlatformException(
                    "Unable to sanitize string '%s' for file name.",
                    value);
        }
        return sanitizedValue;
    }

    /**
     * Ensures that the directory structure represented by the given {@link File} is created.
     */
    private static File createDirectoryStructure(File directoryStructure) throws IOException {
        directoryStructure.mkdirs();
        if (!directoryStructure.isDirectory()) {
            throw new IOException("Unable to create directory structure for "
                    + directoryStructure.getAbsolutePath());
        }
        return directoryStructure;
    }

    /**
     * Validate that a collection is not null or empty.
     *
     * @throws IllegalStateException if collection is null or empty.
     */
    private static <T> void validateCollection(Collection<T> collection) {
        if(collection == null || collection.size() == 0) {
            throw new IllegalStateException("Collection cannot be null or empty");
        }
    }

    public static String getUnitsForSensor(Sensor sensor) {
        switch(sensor.getType()) {
            case Sensor.TYPE_ACCELEROMETER:
                return "m/s^2";
            case Sensor.TYPE_MAGNETIC_FIELD:
            case Sensor.TYPE_MAGNETIC_FIELD_UNCALIBRATED:
                return "uT";
            case Sensor.TYPE_GYROSCOPE:
            case Sensor.TYPE_GYROSCOPE_UNCALIBRATED:
                return "radians/sec";
            case Sensor.TYPE_PRESSURE:
                return "hPa";
        };
        return "";
    }
}