jpountz opened a new pull request, #14979:
URL: https://github.com/apache/lucene/pull/14979
I remember benchmarking prefix sums quite extensively, and unrolled loops
performed significantly better than their rolled on counterpart, both on micro
and macro benchmarks:
```java
private static void prefixSum(int[] arr, int len) {
for (int i = 1; i < len; ++i) {
arr[i] += arr[i-1];
}
}
```
However, I recently discovered that rewriting the loop this way performs
much better, and almost on par with the unrolled variant:
```java
private static void prefixSum(int[] arr, int len) {
int sum = 0;
for (int i = 0; i < len; ++i) {
sum += arr[i];
arr[i] = sum;
}
}
```
I haven't checked the assembly yet, but both a JMH benchmark and luceneutil
agree that it doesn't introduce a slowdown, so I cut over prefix sums to this
approach.
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