Force explicit double -> int conversion for CFeeRate constructor

This resolves an issue where estimatesmartfee would return 999
sat/byte instead of 1000, due to floating point loss of precision

Thanks to sipa for suggesting is_integral.

4 files changed, 13 insertions, 8 deletions

diff --git a/src/policy/feerate.h b/src/policy/feerate.h
index 7e519e3efa..3449cdd699 100644
--- a/src/policy/feerate.h
+++ b/src/policy/feerate.h
@@ -20,10 +20,15 @@ class CFeeRate
 {
 private:
     CAmount nSatoshisPerK; // unit is satoshis-per-1,000-bytes
+
 public:
     /** Fee rate of 0 satoshis per kB */
     CFeeRate() : nSatoshisPerK(0) { }
-    explicit CFeeRate(const CAmount& _nSatoshisPerK): nSatoshisPerK(_nSatoshisPerK) { }
+    template<typename I>
+    CFeeRate(const I _nSatoshisPerK): nSatoshisPerK(_nSatoshisPerK) {
+        // We've previously had bugs creep in from silent double->int conversion...
+        static_assert(std::is_integral<I>::value, "CFeeRate should be used without floats");
+    }
     /** Constructor for a fee rate in satoshis per kB. The size in bytes must not exceed (2^63 - 1)*/
     CFeeRate(const CAmount& nFeePaid, size_t nBytes);
     /**
diff --git a/src/policy/fees.cpp b/src/policy/fees.cpp
index ca774cd74b..8056f385ab 100644
--- a/src/policy/fees.cpp
+++ b/src/policy/fees.cpp
@@ -714,7 +714,7 @@ CFeeRate CBlockPolicyEstimator::estimateRawFee(int confTarget, double successThr
     if (median < 0)
         return CFeeRate(0);
 
-    return CFeeRate(median);
+    return CFeeRate(llround(median));
 }
 
 unsigned int CBlockPolicyEstimator::HighestTargetTracked(FeeEstimateHorizon horizon) const
@@ -901,7 +901,7 @@ CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation
 
     if (median < 0) return CFeeRate(0); // error condition
 
-    return CFeeRate(median);
+    return CFeeRate(llround(median));
 }
 
 
diff --git a/src/test/mempool_tests.cpp b/src/test/mempool_tests.cpp
index 51b28d09fa..116210a297 100644
--- a/src/test/mempool_tests.cpp
+++ b/src/test/mempool_tests.cpp
@@ -559,15 +559,15 @@ BOOST_AUTO_TEST_CASE(MempoolSizeLimitTest)
     // ... we should keep the same min fee until we get a block
     pool.removeForBlock(vtx, 1);
     SetMockTime(42 + 2*CTxMemPool::ROLLING_FEE_HALFLIFE);
-    BOOST_CHECK_EQUAL(pool.GetMinFee(1).GetFeePerK(), (maxFeeRateRemoved.GetFeePerK() + 1000)/2);
+    BOOST_CHECK_EQUAL(pool.GetMinFee(1).GetFeePerK(), llround((maxFeeRateRemoved.GetFeePerK() + 1000)/2.0));
     // ... then feerate should drop 1/2 each halflife
 
     SetMockTime(42 + 2*CTxMemPool::ROLLING_FEE_HALFLIFE + CTxMemPool::ROLLING_FEE_HALFLIFE/2);
-    BOOST_CHECK_EQUAL(pool.GetMinFee(pool.DynamicMemoryUsage() * 5 / 2).GetFeePerK(), (maxFeeRateRemoved.GetFeePerK() + 1000)/4);
+    BOOST_CHECK_EQUAL(pool.GetMinFee(pool.DynamicMemoryUsage() * 5 / 2).GetFeePerK(), llround((maxFeeRateRemoved.GetFeePerK() + 1000)/4.0));
     // ... with a 1/2 halflife when mempool is < 1/2 its target size
 
     SetMockTime(42 + 2*CTxMemPool::ROLLING_FEE_HALFLIFE + CTxMemPool::ROLLING_FEE_HALFLIFE/2 + CTxMemPool::ROLLING_FEE_HALFLIFE/4);
-    BOOST_CHECK_EQUAL(pool.GetMinFee(pool.DynamicMemoryUsage() * 9 / 2).GetFeePerK(), (maxFeeRateRemoved.GetFeePerK() + 1000)/8);
+    BOOST_CHECK_EQUAL(pool.GetMinFee(pool.DynamicMemoryUsage() * 9 / 2).GetFeePerK(), llround((maxFeeRateRemoved.GetFeePerK() + 1000)/8.0));
     // ... with a 1/4 halflife when mempool is < 1/4 its target size
 
     SetMockTime(42 + 7*CTxMemPool::ROLLING_FEE_HALFLIFE + CTxMemPool::ROLLING_FEE_HALFLIFE/2 + CTxMemPool::ROLLING_FEE_HALFLIFE/4);
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index f68d677646..776d3f36ca 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -981,7 +981,7 @@ const CTxMemPool::setEntries & CTxMemPool::GetMemPoolChildren(txiter entry) cons
 CFeeRate CTxMemPool::GetMinFee(size_t sizelimit) const {
     LOCK(cs);
     if (!blockSinceLastRollingFeeBump || rollingMinimumFeeRate == 0)
-        return CFeeRate(rollingMinimumFeeRate);
+        return CFeeRate(llround(rollingMinimumFeeRate));
 
     int64_t time = GetTime();
     if (time > lastRollingFeeUpdate + 10) {
@@ -999,7 +999,7 @@ CFeeRate CTxMemPool::GetMinFee(size_t sizelimit) const {
             return CFeeRate(0);
         }
     }
-    return std::max(CFeeRate(rollingMinimumFeeRate), incrementalRelayFee);
+    return std::max(CFeeRate(llround(rollingMinimumFeeRate)), incrementalRelayFee);
 }
 
 void CTxMemPool::trackPackageRemoved(const CFeeRate& rate) {