src/main/java/com/android/tools/build/apkzlib/zip/utils/MsDosDateTimeUtils.java

/*
 * Copyright (C) 2015 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 com.android.tools.build.apkzlib.zip.utils;

import com.google.common.base.Verify;
import java.util.Calendar;
import java.util.Date;

/**
 * Yes. This actually refers to MS-DOS in 2015. That's all I have to say about legacy stuff.
 */
public class MsDosDateTimeUtils {
    /**
     * Utility class: no constructor.
     */
    private MsDosDateTimeUtils() {
    }

    /**
     * Packs java time value into an MS-DOS time value.
     *
     * @param time the time value
     * @return the MS-DOS packed time
     */
    public static int packTime(long time) {
        Calendar c = Calendar.getInstance();
        c.setTime(new Date(time));

        int seconds = c.get(Calendar.SECOND);
        int minutes = c.get(Calendar.MINUTE);
        int hours = c.get(Calendar.HOUR_OF_DAY);

        /*
         * Here is how MS-DOS packs a time value:
         * 0-4: seconds (divided by 2 because we only have 5 bits = 32 different numbers)
         * 5-10: minutes (6 bits = 64 possible values)
         * 11-15: hours (5 bits = 32 possible values)
         *
         * source: https://msdn.microsoft.com/en-us/library/windows/desktop/ms724247(v=vs.85).aspx
         */
        return (hours << 11) | (minutes << 5) | (seconds / 2);
    }

    /**
     * Packs the current time value into an MS-DOS time value.
     *
     * @return the MS-DOS packed time
     */
    public static int packCurrentTime() {
        return packTime(new Date().getTime());
    }

    /**
     * Packs java time value into an MS-DOS date value.
     *
     * @param time the time value
     * @return the MS-DOS packed date
     */
    public static int packDate(long time) {
        Calendar c = Calendar.getInstance();
        c.setTime(new Date(time));

        /*
         * Even MS-DOS used 1 for January. Someone wasn't really thinking when they decided on Java
         * it would start at 0...
         */
        int day = c.get(Calendar.DAY_OF_MONTH);
        int month = c.get(Calendar.MONTH) + 1;

        /*
         * MS-DOS counts years starting from 1980. Since its launch date was in 81, it was obviously
         * not necessary to talk about dates earlier than that.
         */
        int year = c.get(Calendar.YEAR) - 1980;
        Verify.verify(year >= 0 && year < 128);

        /*
         * Here is how MS-DOS packs a date value:
         * 0-4: day (5 bits = 32 values)
         * 5-8: month (4 bits = 16 values)
         * 9-15: year (7 bits = 128 values)
         *
         * source: https://msdn.microsoft.com/en-us/library/windows/desktop/ms724247(v=vs.85).aspx
         */
        return (year << 9) | (month << 5) | day;
    }

    /**
     * Packs the current time value into an MS-DOS date value.
     *
     * @return the MS-DOS packed date
     */
    public static int packCurrentDate() {
        return packDate(new Date().getTime());
    }
}