uschindler commented on PR #13076:
URL: https://github.com/apache/lucene/pull/13076#issuecomment-1927626207
Hi,
I modified the scalar variant like that:
```java
@Override
public int binaryHammingDistance(byte[] a, byte[] b) {
int distance = 0, i = 0;
for (; i < a.length + 1 - Long.BYTES; i += Long.BYTES) {
distance += Long.bitCount(((long) BitUtil.VH_NATIVE_LONG.get(a, i) ^
(long) BitUtil.VH_NATIVE_LONG.get(b, i)) & 0xFFFFFFFFFFFFFFFFL);
}
// int tail
for (; i < a.length + 1 - Integer.BYTES; i += Integer.BYTES) {
distance += Integer.bitCount(((int) BitUtil.VH_NATIVE_INT.get(a, i) ^
(int) BitUtil.VH_NATIVE_INT.get(b, i)) & 0xFFFFFFFF);
}
// byte tail
for (; i < a.length; i++) {
distance += Integer.bitCount((a[i] ^ b[i]) & 0xFF);
}
return distance;
}
```
This one only uses popcnt CPU instruction. I then ran your benchmakrk to
compare the panama-vectorized one with my new implementation as above:
```
Benchmark (size) Mode Cnt Score
Error Units
VectorUtilBenchmark.binaryHammingDistanceScalar 1 thrpt 15 258,511
± 17,969 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 128 thrpt 15 62,364
± 0,723 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 207 thrpt 15 40,302
± 0,703 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 256 thrpt 15 42,025
± 0,891 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 300 thrpt 15 35,065
± 3,125 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 512 thrpt 15 24,391
± 1,987 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 702 thrpt 15 17,505
± 0,684 ops/us
VectorUtilBenchmark.binaryHammingDistanceScalar 1024 thrpt 15 13,806
± 0,102 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 1 thrpt 15 231,651
± 9,975 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 128 thrpt 15 16,760
± 0,251 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 207 thrpt 15 10,317
± 0,251 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 256 thrpt 15 8,887
± 0,559 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 300 thrpt 15 7,466
± 0,345 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 512 thrpt 15 4,706
± 0,080 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 702 thrpt 15 3,062
± 0,566 ops/us
VectorUtilBenchmark.binaryHammingDistanceVector 1024 thrpt 15 2,404
± 0,024 ops/us
````
Please not the SCALAR one here is the above variant. As this one four (!)
times faster than the Panama variant, there is no need to have a
panama-vectorized one and it looks like it is not working at all. I think the
lookup table is a bad idea.
To make it short:
- Remove the impl and the table from VectorUtilSupport (scalar and
vectorized)
- Implement my above methoid directly in VectorUtil class
This will be a short PR. Make sure to add more tests (there's only one for
the VectorUtil method).
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