refactor: Avoid double to int cast for nCheckFrequency

Use a ratio instead of a frequency that requires a double to int cast
for determining how often a mempool sanity check should run.

Author: ellemouton

src/init.cpp

@@ -1394,10 +1394,8 @@ bool AppInitMain(const util::Ref& context, NodeContext& node, interfaces::BlockA
     assert(!node.mempool);
     node.mempool = MakeUnique<CTxMemPool>(&::feeEstimator);
     if (node.mempool) {
-        int ratio = std::min<int>(std::max<int>(args.GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
-        if (ratio != 0) {
-            node.mempool->setSanityCheck(1.0 / ratio);
-        }
+        int check_ratio = std::min<int>(std::max<int>(args.GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
+        node.mempool->setSanityCheck(check_ratio);
     }
 
     assert(!node.chainman);

src/txmempool.cpp

@@ -339,7 +339,7 @@ CTxMemPool::CTxMemPool(CBlockPolicyEstimator* estimator)
     // Sanity checks off by default for performance, because otherwise
     // accepting transactions becomes O(N^2) where N is the number
     // of transactions in the pool
-    nCheckFrequency = 0;
+    m_check_ratio = 0;
 }
 
 bool CTxMemPool::isSpent(const COutPoint& outpoint) const
@@ -523,7 +523,7 @@ void CTxMemPool::removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMem
                 if (it2 != mapTx.end())
                     continue;
                 const Coin &coin = pcoins->AccessCoin(txin.prevout);
-                if (nCheckFrequency != 0) assert(!coin.IsSpent());
+                if (m_check_ratio != 0) assert(!coin.IsSpent());
                 if (coin.IsSpent() || (coin.IsCoinBase() && ((signed long)nMemPoolHeight) - coin.nHeight < COINBASE_MATURITY)) {
                     txToRemove.insert(it);
                     break;
@@ -620,11 +620,9 @@ static void CheckInputsAndUpdateCoins(const CTransaction& tx, CCoinsViewCache& m
 void CTxMemPool::check(const CCoinsViewCache *pcoins) const
 {
     LOCK(cs);
-    if (nCheckFrequency == 0)
-        return;
+    if (m_check_ratio == 0) return;
 
-    if (GetRand(std::numeric_limits<uint32_t>::max()) >= nCheckFrequency)
-        return;
+    if (GetRand(m_check_ratio) >= 1) return;
 
     LogPrint(BCLog::MEMPOOL, "Checking mempool with %u transactions and %u inputs\n", (unsigned int)mapTx.size(), (unsigned int)mapNextTx.size());
 

src/txmempool.h

@@ -488,7 +488,7 @@ class SaltedTxidHasher
 class CTxMemPool
 {
 private:
-    uint32_t nCheckFrequency GUARDED_BY(cs); //!< Value n means that n times in 2^32 we check.
+    uint32_t m_check_ratio GUARDED_BY(cs); //!< Value n means that 1 times in n we check.
     std::atomic<unsigned int> nTransactionsUpdated; //!< Used by getblocktemplate to trigger CreateNewBlock() invocation
     CBlockPolicyEstimator* minerPolicyEstimator;
 
@@ -611,7 +611,7 @@ class CTxMemPool
      * check does nothing.
      */
     void check(const CCoinsViewCache *pcoins) const;
-    void setSanityCheck(double dFrequency = 1.0) { LOCK(cs); nCheckFrequency = static_cast<uint32_t>(dFrequency * 4294967295.0); }
+    void setSanityCheck(int check_ratio = 0) { LOCK(cs); m_check_ratio = check_ratio; }
 
     // addUnchecked must updated state for all ancestors of a given transaction,
     // to track size/count of descendant transactions.  First version of