Merge "Optimize Message comparison to be branchless." into main

    }

    /*package*/ static int compareMessages(@NonNull Message m1, @NonNull Message m2) {

        if (m1 == m2) {

            return 0;

        }

        // Primary queue order is by when.

        // Messages with an earlier when should come first in the queue.

        final long whenDiff = m1.when - m2.when;

        if (whenDiff > 0) return 1;

        if (whenDiff < 0) return -1;

        // Secondary queue order is by insert sequence.

        // If two messages were inserted with the same `when`, the one inserted

        // first should come first in the queue.

        final long insertSeqDiff = m1.insertSeq - m2.insertSeq;

        if (insertSeqDiff > 0) return 1;

        if (insertSeqDiff < 0) return -1;

        return 0;

        // Implement the comparison with branchless logic.

        final long when1 = m1.when;

        final long when2 = m2.when;

        final long insertSeq1 = m1.insertSeq;

        final long insertSeq2 = m2.insertSeq;

        final int whenSign = Long.signum(when1 - when2);

        final int insertSeqSign = Long.signum(insertSeq1 - insertSeq2);

        // whenSign takes precedence over insertSeqSign, so the formula below is such that

        // insertSeqSign

        // only matters as a tie-breaker if whenSign is 0.

        return whenSign * 2 + insertSeqSign;

    }

    @Override