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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.document;
/**
* A bucket id contains bit used for various purposes. In most use cases, these can use the default
* settings, but the number of bits used for the different purposes is configurable, to allow for
* special uses.
*
* Because of this, bucket ids cannot be generated without knowing how the bucket id is configured to
* be put together, so all bucket ids must be generated by this factory class.
*
* For more information about what the sub parts of a bucket id actually is, read the bucket splitting documentation.
*
* @author Håkon Humberset
*/
public class BucketIdFactory {
private final int gidBits;
private final int locationBits;
private final int countBits;
private final long initialCount;
private final long locationMask;
private final long gidMask;
/** Create a factory, using the default configuration. */
public BucketIdFactory() {
this(32, 26, 6);
}
/**
* Create a factory, using the provided configuration.
* @param gidBits How many bits that are used to specify gidbits.
*/
public BucketIdFactory(int locationBits, int gidBits, int countBits) {
this.locationBits = locationBits;
this.gidBits = gidBits;
this.countBits = countBits;
initialCount = 58l << (64 - countBits);
locationMask = 0xFFFFFFFFFFFFFFFFl >>> (64 - getLocationBitCount());
gidMask = ((0xFFFFFFFFFFFFFFFFl >>> getLocationBitCount()) << (getLocationBitCount() + BucketId.COUNT_BITS)) >>> BucketId.COUNT_BITS;
}
/**
* Create a factory, with parameters gotten from configuration.
* TODO: Not implemented yet
* @param configId The config id from where to get config.
*/
public BucketIdFactory(String configId) {
this(32, 26, 6);
}
/** @return Get number of bits used for storing of LSB part of location.*/
public int getLocationBitCount() { return locationBits; }
/** @return Get number of bits used to specify gid. */
public int getGidBitCount() { return gidBits; }
/** @return Get number of bits used to store bit count used. */
public int getCountBitCount() { return countBits; }
/**
* Get the gid bit contribution in the bucket id, shifted to the correct
* position in the id.
*
* @param gid The gid we need to calculate contribution from.
* @return A mask to or with the bucket id to get the bit set.
*/
private long getGidContribution(byte[] gid) {
long gidbits = 0;
for (int i=4; i<12; ++i) {
gidbits <<= 8;
long tall = gid[15 - i] & 0xFFl;
assert(tall >= 0 && tall <= 255);
gidbits |= tall;
}
return gidbits & gidMask;
}
/**
* Get the bucket id for a given document.
*
* @param doc The doc.
* @return The bucket id.
*/
public BucketId getBucketId(DocumentId doc) {
long location = doc.getScheme().getLocation();
byte[] gid = doc.getGlobalId();
long gidContribution = getGidContribution(gid);
return new BucketId(64 - BucketId.COUNT_BITS, initialCount | (gidMask & gidContribution) | (locationMask & location));
}
}
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