ChrisHegarty commented on code in PR #13545:
URL: https://github.com/apache/lucene/pull/13545#discussion_r1670333682
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lucene/core/src/java/org/apache/lucene/util/VectorUtil.java:
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@@ -212,6 +212,14 @@ public static int int4DotProductPacked(byte[] unpacked,
byte[] packed) {
return IMPL.int4DotProduct(unpacked, false, packed, true);
}
+ /**
+ * For xorBitCount we stride over the values as either 64-bits (long) or
32-bits (int) at a time.
+ * On ARM Long::bitCount is not vectorized, and therefore produces less than
optimal code, when
+ * compared to Integer::bitCount. While Long::bitCount is optimal on x64.
TODO: include the
+ * OpenJDK JIRA url
Review Comment:
Oops. I just added it in
https://github.com/apache/lucene/commit/4baaedaa67046adeed19cdc28a346c1ebc9e8b5d
https://bugs.openjdk.org/browse/JDK-8336000
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