Question

I am really short on time for doing the learning of bitwise operations.
I want to convert large integer(>127) values without doing ‘<<‘ or anything similar.

I need byte representation of integer values used to identify sequence numbers of packets in header sent across UDP. If there is no solution I will introduce two bytes..

Something like: 1, 1 ; 1,2 ; 1,3 ; packet lost ; 1,4 ; packet lost; 2,1 ,2,2
and then reset it upon reaching 127; 127

I can introduce third, but this is rather ugly.

It would be really useful to have black box that is part of java api doing all that byte conversion for me. Is there?

Thanks,

Answer 1

To pack an unsigned 8-bit value into a byte:

static byte toByte(int i) {
  if ((i < 0) || (i > 255))
    throw new IllegalArgumentException(String.valueOf(i));
  return (byte) i;
}

To convert back:

static int toInt(byte b) {
  return (b < 0) ? (b + 256) : b;
}

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After reading your comments on other answers, it sounds like you might want something like this:

byte[] b = BigInteger.valueOf(counter).toByteArray();

and

long counter = new BigInteger(b).longValue();

Since the length of the array would vary as the counter grows, you’d need some way to indicate its length or delimit it. But this technique will convert any integer value to an array of bytes.