Converting 32-bit unsigned integer (big endian) to long and back
25,224
Solution 1
Sounds like a work for the ByteBuffer.
Somewhat like
public static void main(String[] args) {
byte[] payload = toArray(-1991249);
int number = fromArray(payload);
System.out.println(number);
}
public static int fromArray(byte[] payload){
ByteBuffer buffer = ByteBuffer.wrap(payload);
buffer.order(ByteOrder.BIG_ENDIAN);
return buffer.getInt();
}
public static byte[] toArray(int value){
ByteBuffer buffer = ByteBuffer.allocate(4);
buffer.order(ByteOrder.BIG_ENDIAN);
buffer.putInt(value);
buffer.flip();
return buffer.array();
}
Solution 2
You can use ByteBuffer, or you can do it the old-fashioned way:
long result = 0x00FF & byteData[0];
result <<= 8;
result += 0x00FF & byteData[1];
result <<= 8;
result += 0x00FF & byteData[2];
result <<= 8;
result += 0x00FF & byteData[3];
Solution 3
Guava has useful classes for dealing with unsigned numeric values.
Comments
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Aviram almost 2 years
I have a byte[4] which contains a 32-bit unsigned integer (in big endian order) and I need to convert it to long (as int can't hold an unsigned number).
Also, how do I do it vice-versa (i.e. from long that contains a 32-bit unsigned integer to byte[4])?
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Aviram about 12 yearsCorrect me if I'm wrong, but if I do
int value = buffer.getInt();
then int might not be able to contain the whole number (if it is unsigned and not signed). -
Edwin Dalorzo about 12 years@Aviram An integer in Java is 32-bits (4 bytes), as long as your ByteBuffer is 4 bytes long, I do not see why there should be a problem. I have improved my answer and I tested it with positives and negatives and it works just fine so far. May I be missing something? If you intend to use unsigned integers then use longs and not integers, because integers in Java are signed.
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Vishy about 12 yearsYou can use
return buffer.getInt() & 0xFFFFFFFFL;
as you will always get the unsigned value. ByteBuffer's are BIG_ENDIAN by default. You don't need to callflip()
to usearray()
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Emmanuel Touzery over 11 yearsGood point, that is overwise just using the & 0xFFFFFFFFL method described by Peter Lawrey higher in one comment of this question.
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gavioto almost 10 yearsWhy toLong(Integer.MIN_VALUE) doesn't work? and return negative long ideone.com/cERLo1