Backport: Move group-varint encoding/decoding logic to DataOutput/Dat…

…aInput (#12841)

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsReader.java

@@ -149,7 +149,7 @@ static void readVIntBlock(
       boolean indexHasFreq,
       boolean decodeFreq)
       throws IOException {
-    GroupVIntReader.readValues(docIn, docBuffer, num);
+    docIn.readGroupVInts(docBuffer, num);
     if (indexHasFreq && decodeFreq) {
       for (int i = 0; i < num; ++i) {
         freqBuffer[i] = docBuffer[i] & 0x01;

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99PostingsWriter.java

@@ -92,7 +92,6 @@ public final class Lucene99PostingsWriter extends PushPostingsWriterBase {
   private final PForUtil pforUtil;
   private final ForDeltaUtil forDeltaUtil;
   private final Lucene99SkipWriter skipWriter;
-  private final GroupVIntWriter docGroupVIntWriter;
 
   private boolean fieldHasNorms;
   private NumericDocValues norms;
@@ -173,7 +172,6 @@ public Lucene99PostingsWriter(SegmentWriteState state) throws IOException {
     skipWriter =
         new Lucene99SkipWriter(
             MAX_SKIP_LEVELS, BLOCK_SIZE, state.segmentInfo.maxDoc(), docOut, posOut, payOut);
-    docGroupVIntWriter = new GroupVIntWriter();
   }
 
   @Override
@@ -378,7 +376,7 @@ public void finishTerm(BlockTermState _state) throws IOException {
           docDeltaBuffer[i] = (docDeltaBuffer[i] << 1) | (freqBuffer[i] == 1 ? 1 : 0);
         }
       }
-      docGroupVIntWriter.writeValues(docOut, docDeltaBuffer, docBufferUpto);
+      docOut.writeGroupVInts(docDeltaBuffer, docBufferUpto);
       if (writeFreqs) {
         for (int i = 0; i < docBufferUpto; i++) {
           final int freq = (int) freqBuffer[i];

lucene/core/src/java/org/apache/lucene/store/BufferedIndexInput.java

@@ -20,6 +20,7 @@
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
+import org.apache.lucene.util.GroupVIntUtil;
 
 /** Base implementation class for buffered {@link IndexInput}. */
 public abstract class BufferedIndexInput extends IndexInput implements RandomAccessInput {
@@ -149,6 +150,16 @@ public final int readInt() throws IOException {
     }
   }
 
+  @Override
+  protected void readGroupVInt(long[] dst, int offset) throws IOException {
+    final int len =
+        GroupVIntUtil.readGroupVInt(
+            this, buffer.remaining(), p -> buffer.getInt((int) p), buffer.position(), dst, offset);
+    if (len > 0) {
+      buffer.position(buffer.position() + len);
+    }
+  }
+
   @Override
   public final long readLong() throws IOException {
     if (Long.BYTES <= buffer.remaining()) {

lucene/core/src/java/org/apache/lucene/store/ByteBuffersDataInput.java

@@ -29,6 +29,7 @@
 import java.util.Locale;
 import java.util.stream.Collectors;
 import org.apache.lucene.util.Accountable;
+import org.apache.lucene.util.GroupVIntUtil;
 import org.apache.lucene.util.RamUsageEstimator;
 
 /**
@@ -212,6 +213,25 @@ public long readLong() throws IOException {
     }
   }
 
+  @Override
+  protected void readGroupVInt(long[] dst, int offset) throws IOException {
+    final ByteBuffer block = blocks[blockIndex(pos)];
+    final int blockOffset = blockOffset(pos);
+    // We MUST save the return value to local variable, could not use pos += readGroupVInt(...).
+    // because `pos +=` in java will move current value(not address) of pos to register first,
+    // then call the function, but we will update pos value in function via readByte(), then
+    // `pos +=` will use an old pos value plus return value, thereby missing 1 byte.
+    final int len =
+        GroupVIntUtil.readGroupVInt(
+            this,
+            block.limit() - blockOffset,
+            p -> block.getInt((int) p),
+            blockOffset,
+            dst,
+            offset);
+    pos += len;
+  }
+
   @Override
   public long length() {
     return length;

lucene/core/src/java/org/apache/lucene/store/ByteBuffersIndexInput.java

@@ -199,6 +199,12 @@ public void readLongs(long[] dst, int offset, int length) throws IOException {
     in.readLongs(dst, offset, length);
   }
 
+  @Override
+  protected void readGroupVInt(long[] dst, int offset) throws IOException {
+    ensureOpen();
+    in.readGroupVInt(dst, offset);
+  }
+
   @Override
   public IndexInput clone() {
     ensureOpen();

lucene/core/src/java/org/apache/lucene/store/DataInput.java

@@ -27,6 +27,7 @@
 import java.util.TreeMap;
 import java.util.TreeSet;
 import org.apache.lucene.util.BitUtil;
+import org.apache.lucene.util.GroupVIntUtil;
 
 /**
  * Abstract base class for performing read operations of Lucene's low-level data types.
@@ -98,6 +99,32 @@ public int readInt() throws IOException {
     return ((b4 & 0xFF) << 24) | ((b3 & 0xFF) << 16) | ((b2 & 0xFF) << 8) | (b1 & 0xFF);
   }
 
+  /**
+   * Read all the group varints, including the tail vints. we need a long[] because this is what
+   * postings are using, all longs are actually required to be integers.
+   *
+   * @param dst the array to read ints into.
+   * @param limit the number of int values to read.
+   * @lucene.experimental
+   */
+  public final void readGroupVInts(long[] dst, int limit) throws IOException {
+    int i;
+    for (i = 0; i <= limit - 4; i += 4) {
+      readGroupVInt(dst, i);
+    }
+    for (; i < limit; ++i) {
+      dst[i] = readVInt();
+    }
+  }
+
+  /**
+   * Override if you have a efficient implementation. In general this is when the input supports
+   * random access.
+   */
+  protected void readGroupVInt(long[] dst, int offset) throws IOException {
+    GroupVIntUtil.readGroupVInt(this, dst, offset);
+  }
+
   /**
    * Reads an int stored in variable-length format. Reads between one and five bytes. Smaller values
    * take fewer bytes. Negative numbers are supported, but should be avoided.

lucene/core/src/java/org/apache/lucene/store/DataOutput.java

@@ -21,6 +21,7 @@
 import java.util.Set;
 import org.apache.lucene.util.BitUtil;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.BytesRefBuilder;
 
 /**
  * Abstract base class for performing write operations of Lucene's low-level data types.
@@ -29,6 +30,7 @@
  * internal state like file position).
  */
 public abstract class DataOutput {
+  private final BytesRefBuilder groupVIntBytes = new BytesRefBuilder();
 
   /**
    * Writes a single byte.
@@ -322,4 +324,43 @@ public void writeSetOfStrings(Set<String> set) throws IOException {
       writeString(value);
     }
   }
+
+  /**
+   * Encode integers using group-varint. It uses {@link DataOutput#writeVInt VInt} to encode tail
+   * values that are not enough for a group. we need a long[] because this is what postings are
+   * using, all longs are actually required to be integers.
+   *
+   * @param values the values to write
+   * @param limit the number of values to write.
+   * @lucene.experimental
+   */
+  public void writeGroupVInts(long[] values, int limit) throws IOException {
+    int off = 0;
+
+    // encode each group
+    while ((limit - off) >= 4) {
+      byte flag = 0;
+      groupVIntBytes.setLength(1);
+      flag |= (encodeGroupValue(Math.toIntExact(values[off++])) - 1) << 6;
+      flag |= (encodeGroupValue(Math.toIntExact(values[off++])) - 1) << 4;
+      flag |= (encodeGroupValue(Math.toIntExact(values[off++])) - 1) << 2;
+      flag |= (encodeGroupValue(Math.toIntExact(values[off++])) - 1);
+      groupVIntBytes.setByteAt(0, flag);
+      writeBytes(groupVIntBytes.bytes(), groupVIntBytes.length());
+    }
+
+    // tail vints
+    for (; off < limit; off++) {
+      writeVInt(Math.toIntExact(values[off]));
+    }
+  }
+
+  private int encodeGroupValue(int v) {
+    int lastOff = groupVIntBytes.length();
+    do {
+      groupVIntBytes.append((byte) (v & 0xFF));
+      v >>>= 8;
+    } while (v != 0);
+    return groupVIntBytes.length() - lastOff;
+  }
 }