**Use case**
Clickhouse version 21.4
```
SELECT
    quantileTiming(0.95)(key) AS timing,
    quantileExact(0.95)(key) AS exact,
    quantileTDigest(0.95)(key) AS tdigest
FROM
(
    SELECT
        9000 AS key,
        2 AS count
    UNION ALL
    SELECT
        3000,
        11
    UNION ALL
    SELECT
        1000,
        26
)
ARRAY JOIN range(count) AS s

Query id: addce63f-0b75-46e2-b896-712d66711fb0

┌─timing─┬─exact─┬──tdigest─┐
│   9000 │  9000 │ 8123.076 │
└────────┴───────┴──────────┘


SELECT
    quantileTiming(0.9)(key) AS timing,
    quantileExact(0.9)(key) AS exact,
    quantileTDigest(0.9)(key) AS tdigest
FROM
(
    SELECT key
    FROM
    (
        SELECT
            9000 AS key,
            2 AS count
        UNION ALL
        SELECT
            3000,
            11
        UNION ALL
        SELECT
            1000,
            26
    )
    ARRAY JOIN range(count) AS s
    ORDER BY key ASC
)

Query id: e92e3d07-3b97-4155-aa10-9a15544d9312

┌─timing─┬─exact─┬───tdigest─┐
│   3000 │  3000 │ 6323.0757 │
└────────┴───────┴───────────┘

```

Probably related: https://github.com/tdunning/t-digest/issues/154
{
        if (unmerged > 0 || centroids.size() > params.max_centroids)
        {
            
            RadixSort<RadixSortTraits>::executeLSD(centroids.data(), centroids.size());
            
            auto l = centroids.begin();
            auto r = std::next(l);
            const BetterFloat count_epsilon_4 = count * params.epsilon * 4; 
            BetterFloat sum = 0;
            BetterFloat l_mean = l->mean; 
            BetterFloat l_count = l->count;
            while (r != centroids.end())
            {
                if (l->mean == r->mean) 
                {
                    l_count += r->count;
                    l->count = l_count;
                    ++r;
                    continue;