gf2121 commented on issue #12639:
URL: https://github.com/apache/lucene/issues/12639#issuecomment-1752926917
> is it the number of longs or the number of bits?
It is the number of longs. Here is the whole class:
```
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@State(Scope.Benchmark)
@Warmup(iterations = 3, time = 3)
@Measurement(iterations = 5, time = 3)
@Fork(value = 1, jvmArgsPrepend = {"--add-modules=jdk.incubator.vector"})
public class BitcountBenchmark {
static final VectorSpecies<Long> PREFERRED_LONG_SPECIES
= LongVector.SPECIES_MAX.withShape(
VectorShape.forBitSize(IntVector.SPECIES_PREFERRED.vectorBitSize()
<< 1));
private long[] longs;
@Param({"1024"})
int size;
@Setup(Level.Trial)
public void init() {
longs = new long[size];
for (int i = 0; i < size; i++) {
longs[i] = ThreadLocalRandom.current().nextLong();
}
if (bitCountOld() != bitCountNew()) {
throw new RuntimeException("New is wrong");
}
if (bitCountOld() != bitCountNewInt()) {
throw new RuntimeException("New is wrong");
}
}
@Benchmark
public int bitCountOld() {
int sum = 0;
for (int i = 0; i < size; i++) {
sum += Long.bitCount(longs[i]);
}
return sum;
}
@Benchmark
public int bitCountNew() {
int i = 0;
int res = 0;
int upperBound = PREFERRED_LONG_SPECIES.loopBound(longs.length);
LongVector acc = LongVector.zero(PREFERRED_LONG_SPECIES);
for (; i < upperBound; i += PREFERRED_LONG_SPECIES.length()) {
LongVector longVector = LongVector.fromArray(PREFERRED_LONG_SPECIES,
longs, i);
LongVector bitCount = longVector.lanewise(VectorOperators.BIT_COUNT);
acc = acc.add(bitCount);
}
res += (int) acc.reduceLanes(VectorOperators.ADD);
for (; i < longs.length; i++) {
res += Long.bitCount(longs[i]);
}
return res;
}
}
```
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