BitSet to and from integer/long
JavaBit ManipulationBitsetJava Problem Overview
If I have an integer that I'd like to perform bit manipulation on, how can I load it into a java.util.BitSet
? How can I convert it back to an int or long? I'm not so concerned about the size of the BitSet
-- it will always be 32 or 64 bits long. I'd just like to use the set()
, clear()
, nextSetBit()
, and nextClearBit()
methods rather than bitwise operators, but I can't find an easy way to initialize a bit set with a numeric type.
Java Solutions
Solution 1 - Java
The following code creates a bit set from a long value and vice versa:
public class Bits {
public static BitSet convert(long value) {
BitSet bits = new BitSet();
int index = 0;
while (value != 0L) {
if (value % 2L != 0) {
bits.set(index);
}
++index;
value = value >>> 1;
}
return bits;
}
public static long convert(BitSet bits) {
long value = 0L;
for (int i = 0; i < bits.length(); ++i) {
value += bits.get(i) ? (1L << i) : 0L;
}
return value;
}
}
EDITED: Now both directions, @leftbrain: of cause, you are right
Solution 2 - Java
Add to finnw answer: there are also BitSet.valueOf(long[])
and BitSet.toLongArray()
. So:
int n = 12345;
BitSet bs = BitSet.valueOf(new long[]{n});
long l = bs.toLongArray()[0];
Solution 3 - Java
Java 7 has BitSet.valueOf(byte[])
and BitSet.toByteArray()
If you are stuck with Java 6 or earlier, you can use BigInteger
if it is not likely to be a performance bottleneck - it has getLowestSetBit
, setBit
and clearBit
methods (the last two will create a new BigInteger
instead of modifying in-place.)
Solution 4 - Java
To get a long
back from a small BitSet
in a 'streamy' way:
long l = bitSet.stream()
.takeWhile(i -> i < Long.SIZE)
.mapToLong(i -> 1L << i)
.reduce(0, (a, b) -> a | b);
Vice-versa:
BitSet bitSet = IntStream.range(0, Long.SIZE - 1)
.filter(i -> 0 != (l & 1L << i))
.collect(BitSet::new, BitSet::set, BitSet::or);
N.B.: Using BitSet::valueOf
and BitSet::toLongArray
is of course easier.
Solution 5 - Java
Pretty much straight from the documentation of nextSetBit
value=0;
for (int i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i+1)) {
value += (1 << i)
}
Solution 6 - Java
Isn't the public void set(int bit)
method what your looking for?