* @return the deserialized HLL. This will never be <code>null</code>.
*
* @see #toBytes(ISchemaVersion)
*/
public static HLL fromBytes(final byte[] bytes) {
final ISchemaVersion schemaVersion = SerializationUtil.getSchemaVersion(bytes);
final IHLLMetadata metadata = schemaVersion.readMetadata(bytes);
final HLLType type = metadata.HLLType();
final int regwidth = metadata.registerWidth();
final int log2m = metadata.registerCountLog2();
final boolean sparseon = metadata.sparseEnabled();
final int expthresh;
if(metadata.explicitAuto()) {
expthresh = -1;
} else if(metadata.explicitOff()) {
expthresh = 0;
} else {
// NOTE: take into account that the postgres-compatible constructor
// subtracts one before taking a power of two.
expthresh = metadata.log2ExplicitCutoff() + 1;
}
final HLL hll = new HLL(log2m, regwidth, expthresh, sparseon, type);
// Short-circuit on empty, which needs no other deserialization.
if(HLLType.EMPTY.equals(type)) {
return hll;
}
final int wordLength;
switch(type) {
case EXPLICIT:
wordLength = Long.SIZE;
break;
case SPARSE:
wordLength = hll.shortWordLength;
break;
case FULL:
wordLength = hll.regwidth;
break;
default:
throw new RuntimeException("Unsupported HLL type " + type);
}
final IWordDeserializer deserializer =
schemaVersion.getDeserializer(type, wordLength, bytes);
switch(type) {
case EXPLICIT:
// NOTE: This should not exceed expthresh and this will always
// be exactly the number of words that were encoded,
// because the word length is at least a byte wide.