1 package org.apache.lucene.util.encoding;
3 import java.io.IOException;
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23 * A {@link ChunksIntEncoder} which encodes data in chunks of 8. Every group starts with a single
24 * byte (called indicator) which represents 8 - 1 bit flags, where the value:
26 * <li>1 means the encoded value is '1'
27 * <li>0 means the value is encoded using {@link VInt8IntEncoder}, and the
28 * encoded bytes follow the indicator.<br>
29 * Since value 0 is illegal, and 1 is encoded in the indicator, the actual
30 * value that is encoded is <code>value-2</code>, which saves some more bits.
34 * <li>Original values: 6, 16, 5, 9, 7, 1
35 * <li>After sorting: 1, 5, 6, 7, 9, 16
36 * <li>D-Gap computing: 1, 4, 1, 1, 2, 5 (so far - done by
37 * {@link DGapIntEncoder})
38 * <li>Encoding: 1,0,1,1,0,0,0,0 as the indicator, by 2 (4-2), 0 (2-2), 3 (5-2).
39 * <li>Binary encode: <u>0 | 0 | 0 | 0 | 1 | 1 | 0 | 1</u> 00000010 00000000
40 * 00000011 (indicator is <u>underlined</u>).<br>
41 * <b>NOTE:</b> the order of the values in the indicator is lsb ⇒ msb,
42 * which allows for more efficient decoding.
45 * @lucene.experimental
47 public class EightFlagsIntEncoder extends ChunksIntEncoder {
50 * Holds all combinations of <i>indicator</i> flags for fast encoding (saves
51 * time on bit manipulation at encode time)
53 private static byte[] encodeTable = new byte[] { 0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, (byte) 0x80 };
55 public EightFlagsIntEncoder() {
60 public void encode(int data) throws IOException {
62 indicator |= encodeTable[ordinal];
64 encodeQueue[encodeQueueSize++] = data - 2;
68 // If 8 values were encoded thus far, 'flush' them including the indicator.
69 if ((ordinal & 0x7) == 0) {
75 public IntDecoder createMatchingDecoder() {
76 return new EightFlagsIntDecoder();
80 public String toString() {
81 return "EightFlags (" + encoder.toString() + ")";