Question

Is there an easy and fast way to convert a Java signed long to an unsigned long string?

-1                    ->  "18446744073709551615"
-9223372036854775808  ->  "09223372036854775808"
 9223372036854775807  ->  "09223372036854775807"
 0                    ->  "00000000000000000000"

Answer 1

Here is a solution using BigInteger:

/** the constant 2^64 */
private static final BigInteger TWO_64 = BigInteger.ONE.shiftLeft(64);

public String asUnsignedDecimalString(long l) {
   BigInteger b = BigInteger.valueOf(l);
   if(b.signum() < 0) {
      b = b.add(TWO_64);
   }
   return b.toString();
}

This works since the unsigned value of a (signed) number in two-s complement is just 2^{(number of bits)} more than the signed value, and Java’s long has 64 bits.

And BigInteger has this nice toString() method which we can use here.