Merge bitcoin/bitcoin#27319: addrman, refactor: improve stochastic test in AddSingle

e064487 addrman, refactor: improve stochastic test in `AddSingle` (brunoerg)

Pull request description:

  This PR changes this algorithm to be O(1) instead of O(n). Also, in the current implementation, if `pinfo->nRefCount` is 0, we created an unnecessary variable (`nFactor`), this changes it. the change is relatively simple and does not cause conflicts.

ACKs for top commit:
  achow101:
    ACK e064487
  amitiuttarwar:
    ACK e064487
  stratospher:
    ACK e064487. simple use of << instead of a loop, didn't observe any behaviour difference before and after.

Tree-SHA512: ff0a65155e47f65d2ce3cb5a3fd7a86efef1861181143df13a9d8e59cb16aee9be2f8801457bba8478b17fac47b015bff5cc656f6fac2ccc071ee7178a38d291

Author: achow101

src/addrman.cpp

@@ -585,11 +585,10 @@ bool AddrManImpl::AddSingle(const CAddress& addr, const CNetAddr& source, std::c
             return false;
 
         // stochastic test: previous nRefCount == N: 2^N times harder to increase it
-        int nFactor = 1;
-        for (int n = 0; n < pinfo->nRefCount; n++)
-            nFactor *= 2;
-        if (nFactor > 1 && (insecure_rand.randrange(nFactor) != 0))
-            return false;
+        if (pinfo->nRefCount > 0) {
+            const int nFactor{1 << pinfo->nRefCount};
+            if (insecure_rand.randrange(nFactor) != 0) return false;
+        }
     } else {
         pinfo = Create(addr, source, &nId);
         pinfo->nTime = std::max(NodeSeconds{0s}, pinfo->nTime - time_penalty);