Java: signed long to unsigned long string

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.

Answer 2

Java 8 includes some support for unsigned longs. If you don't need the zero padding, just do:

Long.toUnsignedString(n); 

If you need zero padding, formatting doesn't work for unsigned longs. However this workaround does an unsigned divide by 10 to drop the unsigned value to a point where it can be represented without the sign bit in the long:

String.format("%019d%d", Long.divideUnsigned(n, 10), Long.remainderUnsigned(n, 10));