jpountz commented on PR #14203:
URL: https://github.com/apache/lucene/pull/14203#issuecomment-2726015514
Thanks for running benchmarks. So it looks like the JVM doesn't think these
shorter loops (with step 128) are worth unrolling? This makes me wonder how
something like that performs on your AVX-512 CPU. I think you had something
similar in one of your previous iterations. On my machine it's on par with the
current version.
```java
private void readInts24(IndexInput in, int count, int[] docIDs) throws
IOException {
if (count == BKDConfig.DEFAULT_MAX_POINTS_IN_LEAF_NODE) {
// Same format, but enabling the JVM to specialize the decoding logic
for the default number
// of points per node proved to help on benchmarks
doReadInts24(in, 512, docIDs);
} else {
doReadInts24(in, count, docIDs);
}
}
private void doReadInts24(IndexInput in, int count, int[] docIDs) throws
IOException {
// Read the first (count - count % 4) values
int quarter = count >> 2;
int numBytes = quarter * 3;
in.readInts(scratch, 0, numBytes);
for (int i = 0; i < numBytes; ++i) {
docIDs[i] = scratch[i] >>> 8;
scratch[i] &= 0xFF;
}
for (int i = 0; i < quarter; ++i) {
docIDs[numBytes + i] = scratch[i]
| (scratch[quarter + i] << 8)
| (scratch[2 * quarter + i] << 16);
}
// Now read the remaining 0, 1, 2 or 3 values
for (int i = quarter << 2; i < count; ++i) {
docIDs[i] = (in.readShort() & 0xFFFF) | (in.readByte() & 0xFF) << 16;
}
}
```
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