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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.prelude.fastsearch;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
/**
* An instance of a document summary, backed by binary data, which decodes and returns fields on request,
* using the (shared) definition of this docsum.
*
* @author Steinar Knutsen
*/
public final class Docsum {
private final DocsumDefinition definition;
private final byte[] packet;
/** The offsets into the packet data of each field, given the fields index, computed lazily */
private final int[] fieldOffsets;
/** The largest stored offset */
private int largestStoredOffset = -1;
public Docsum(DocsumDefinition definition, byte[] packet) {
this.definition = definition;
this.packet = packet;
fieldOffsets=new int[definition.getFieldCount()];
}
public DocsumDefinition getDefinition() { return definition; }
public Object decode(int fieldIndex) {
ByteBuffer b=packetAsBuffer();
setAndReturnOffsetToField(b, fieldIndex);
return definition.getField(fieldIndex).decode(b);
}
public ByteBuffer packetAsBuffer() {
ByteBuffer buffer = ByteBuffer.wrap(packet);
buffer.order(ByteOrder.LITTLE_ENDIAN);
buffer.getInt(); // Skip class id
return buffer;
}
/** Returns the offset of a given field in the buffer, and sets the position of the buffer to that field start */
private int setAndReturnOffsetToField(ByteBuffer b, int fieldIndex) {
// find and store missing offsets up to fieldIndex
if (largestStoredOffset<0) { // initial case
fieldOffsets[0]=b.position();
largestStoredOffset++;
}
while (largestStoredOffset < fieldIndex) { // induction
int offsetOfLargest=fieldOffsets[largestStoredOffset];
b.position(offsetOfLargest);
fieldOffsets[largestStoredOffset+1]=offsetOfLargest+definition.getField(largestStoredOffset).getLength(b);
largestStoredOffset++;
}
// return the stored offset
int offset=fieldOffsets[fieldIndex];
b.position(offset);
return offset;
}
public String toString() {
return "docsum [definition: " + definition + "]";
}
}
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