jpountz commented on a change in pull request #973: LUCENE-9027: Use SIMD 
instructions to decode postings.
URL: https://github.com/apache/lucene-solr/pull/973#discussion_r345832291
 
 

 ##########
 File path: lucene/core/src/java/org/apache/lucene/codecs/lucene84/PForUtil.java
 ##########
 @@ -0,0 +1,126 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.codecs.lucene84;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+import org.apache.lucene.store.DataInput;
+import org.apache.lucene.store.DataOutput;
+import org.apache.lucene.util.packed.PackedInts;
+
+final class PForUtil {
+
+  private static boolean allEqual(long[] l) {
+    for (int i = 1; i < ForUtil.BLOCK_SIZE; ++i) {
+      if (l[i] != l[0]) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private final ForUtil forUtil;
+
+  PForUtil(ForUtil forUtil) {
+    this.forUtil = forUtil;
+  }
+
+  /**
+   * Encode 128 8-bits integers from {@code data} into {@code out}.
+   */
+  void encode(long[] longs, DataOutput out) throws IOException {
+    // At most 3 exceptions
+    final long[] top4 = new long[4];
+    Arrays.fill(top4, -1L);
+    for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) {
+      if (longs[i] > top4[0]) {
+        top4[0] = longs[i];
+        Arrays.sort(top4);
+      }
+    }
+
+    final int maxBitsRequired = PackedInts.bitsRequired(top4[3]);
+    // We store the patch on a byte, so we can't decrease the number of bits 
required by more than 8
+    final int patchedBitsRequired =  
Math.max(PackedInts.bitsRequired(top4[0]), maxBitsRequired - 8);
+    int numExceptions = 0;
+    for (int i = 1; i < 4; ++i) {
+      if (top4[i] > (1L << patchedBitsRequired) - 1) {
+        numExceptions++;
+      }
+    }
+    final byte[] exceptions = new byte[numExceptions*2];
+    if (numExceptions > 0) {
+      int exceptionCount = 0;
+      for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) {
+        if (longs[i] > (1L << patchedBitsRequired) - 1) {
+          exceptions[exceptionCount*2] = (byte) i;
+          exceptions[exceptionCount*2+1] = (byte) (longs[i] >>> 
patchedBitsRequired);
+          longs[i] &= (1L << patchedBitsRequired) - 1;
+          exceptionCount++;
+        }
+      }
+      assert exceptionCount == numExceptions : exceptionCount + " " + 
numExceptions;
+    }
+
+    if (allEqual(longs) && maxBitsRequired <= 8) {
 
 Review comment:
   All values in `longs` have been masked at this point, so there might be 
exceptions. My intuition is that this case is important for rare terms that 
might have most of their term freqs equal to 1, but maybe a couple exceptions. 
Does it answer your question?

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
us...@infra.apache.org


With regards,
Apache Git Services

---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org
For additional commands, e-mail: issues-h...@lucene.apache.org

Reply via email to