rmuir commented on a change in pull request #710:
URL: https://github.com/apache/lucene/pull/710#discussion_r814137771
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File path: lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java
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@@ -176,6 +176,30 @@ public int cardinality() {
return (int) BitUtil.pop_array(bits, 0, numWords);
}
+ @Override
+ public int approximateCardinality() {
+ // Naive sampling: compute the number of bits that are set on the first 16
longs every 1024
+ // longs and scale the result by 1024/16.
+ // This computes the pop count on ranges instead of single longs in order
to take advantage of
+ // vectorization.
+
+ final int rangeLength = 16;
+ final int interval = 1024;
+
+ if (numWords < interval) {
+ return cardinality();
+ }
+
+ long popCount = 0;
+ int maxWord;
+ for (maxWord = 0; maxWord + interval < numWords; maxWord += interval) {
+ popCount += BitUtil.pop_array(bits, maxWord, rangeLength);
Review comment:
this isn't related/review comment. just saying i would be in favor of
removing these `BitUtil` methods as I think they are outdated and provide no
value. I think it would be easier on our eyes to just see loops with
Long.bitCount?
The other constants/methods in the `BitUtil` class actually provide value.
But let's not wrap what the JDK provides efficiently for no reason?
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