rmuir commented on code in PR #15116:
URL: https://github.com/apache/lucene/pull/15116#discussion_r2294901684
##########
lucene/core/src/java/org/apache/lucene/util/GroupVIntUtil.java:
##########
@@ -57,13 +59,44 @@ public static void readGroupVInts(DataInput in, int[] dst,
int limit) throws IOE
* @param offset the offset in the array to start storing ints.
*/
public static void readGroupVInt(DataInput in, int[] dst, int offset) throws
IOException {
+ readGroupVInt(true, in, dst, offset);
+ }
+
+ /** DO not use! Only visible for benchmarking purposes! */
+ public static void readGroupVInt$Baseline(DataInput in, int[] dst, int
offset)
+ throws IOException {
+ readGroupVInt(false, in, dst, offset);
+ }
+
+ private static void readGroupVInt(boolean optimized, DataInput in, int[]
dst, int offset)
+ throws IOException {
final int flag = in.readByte() & 0xFF;
final int n1Minus1 = flag >> 6;
final int n2Minus1 = (flag >> 4) & 0x03;
final int n3Minus1 = (flag >> 2) & 0x03;
final int n4Minus1 = flag & 0x03;
+ // if our DataInput implements RandomAccessInput for absolute access and
IndexInput for seeking,
+ // we use a branch-less implementation:
+ if (optimized && in instanceof RandomAccessInput rin && in instanceof
IndexInput iin) {
Review Comment:
just wondering, if e.g. RandomAccessInput implied IndexInput, maybe we could
even put the readGroupVint() there on RandomAccessInput instead of DataInput.
let it always be optimized and there's no other slow way? At least we should
look to see what is possible to remove checks and just have more sanity.
I don't know if there are cases in the java classes that would make this not
doable.
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