go tdigest: only create a newLocalRNG if one is not provided by options

Allocating and seeding rand objects can be a surprisingly expensive operation.

Especially if the user is already re-using RNGs, or needs to generate their own for
whatever reason, this extra setup can be a lot of overhead for an object that does
not get used.

Id: 428259572af62bcb45505af43359283c95524c65
Author: Zach Dylag
Commit time: 2022-10-07T13:47:57-07:00

Modified tdigest.go

@@ -55,7 +55,6
tdigest := &TDigest{
compression: 100,
count: 0,
- rng: newLocalRNG(1),
}

for _, option := range options {

@@ -63,6 +62,10
if err != nil {
return nil, err
}
+ }
+
+ if tdigest.rng == nil {
+ tdigest.rng = newLocalRNG(1)
}

return tdigest, nil