CODEWITHSUNDEEP
javaandroidtimestampbluetooth-lowenergyunix-timestamp
Adnan
Adnan

Reputation: 8180

Current time as 32­bit UNIX timestamp and time offset

I working with android BLE.

Need to write to characteristic Current time as 32­bit UNIX timestamp. After that write Current timezone offset from UTC in seconds. Probably problem is in coverting to 32 byte array but i am not 100% sure.

I did it but something is wrong. It rises very quickly, and eventually passes 0x7FFF,FFFF, i.e. it overflows and becomes negative as timestamp is a signed integer.

    private byte[] getCurrentUnixTime() {
        int unixTime = (int) (System.currentTimeMillis() / 1000L);
        byte[] currentDate = Converter.intTo32ByteArray(unixTime);
        return currentDate;
    }



    private byte[] getCurrentTimeOffset() {
        TimeZone tz = TimeZone.getDefault();
        Date timeNow = new Date();
        int offsetFromUtc = tz.getOffset(timeNow.getTime()) / 1000;
        byte[] offsetFromUtcByteArray = Converter.intTo32ByteArray(offsetFromUtc);
        return offsetFromUtcByteArray;
    }



public static byte[] intTo32ByteArray(int number) {

        byte[] byteArray = new byte[]{
                (byte) (number >> 24),
                (byte) (number >> 16),
                (byte) (number >> 8),
                (byte) number

        };
        return byteArray;
    }

Upvotes: 1

Views: 1626

Answers (2)

Adnan
Adnan

Reputation: 8180

I resolve problem with this int to byte array code conversion

byte[] offsetFromUtcByteArray = ByteBuffer.allocate(4).order(LITTLE_ENDIAN).putInt((int) offsetFromUtc).array();

and 

 byte[] currentDate = ByteBuffer.allocate(4).order(LITTLE_ENDIAN).putInt((int) unixTime).array();

Upvotes: 0

Krystian Kaniowski
Krystian Kaniowski

Reputation: 2417

Following this you are using rigth conversion.

In java

by default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -0x7FFFFFFF and a maximum value of 0x7FFFFFFF-1 oracle.

So it just a problem with presentation (not data). There's similar case with repesentating colors with int via ARGB - it needs 4*8 bits so value is once positvie, else negative if you want just display that.

To display desirable value you can convert byte[] to long like in this example

Upvotes: 1

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