Type-safe CFeeRate class

Use CFeeRate instead of an int64_t for quantities that are
fee-per-size.

Helps prevent unit-conversion mismatches between the wallet,
relaying, and mining code.

1 files changed, 30 insertions, 7 deletions

diff --git a/src/core.h b/src/core.h
index ba7f691119..9fccffc4b2 100644
--- a/src/core.h
+++ b/src/core.h
@@ -112,6 +112,28 @@ public:
 
 
 
+/** Type-safe wrapper class to for fee rates
+ * (how much to pay based on transaction size)
+ */
+class CFeeRate
+{
+private:
+    int64_t nSatoshisPerK; // unit is satoshis-per-1,000-bytes
+public:
+    explicit CFeeRate(int64_t _nSatoshisPerK): nSatoshisPerK(_nSatoshisPerK) { }
+    CFeeRate(int64_t nFeePaid, size_t nSize);
+    CFeeRate(const CFeeRate& other) { nSatoshisPerK = other.nSatoshisPerK; }
+
+    int64_t GetFee(size_t size); // unit returned is satoshis
+    int64_t GetFeePerK() { return GetFee(1000); } // satoshis-per-1000-bytes
+
+    friend bool operator<(const CFeeRate& a, const CFeeRate& b) { return a.nSatoshisPerK < b.nSatoshisPerK; }
+    friend bool operator>(const CFeeRate& a, const CFeeRate& b) { return a.nSatoshisPerK > b.nSatoshisPerK; }
+    friend bool operator==(const CFeeRate& a, const CFeeRate& b) { return a.nSatoshisPerK == b.nSatoshisPerK; }
+
+    std::string ToString() const;
+};
+
 
 /** An output of a transaction.  It contains the public key that the next input
  * must be able to sign with to claim it.
@@ -148,17 +170,18 @@ public:
 
     uint256 GetHash() const;
 
-    bool IsDust(int64_t nMinRelayTxFee) const
+    bool IsDust(CFeeRate minRelayTxFee) const
     {
-        // "Dust" is defined in terms of CTransaction::nMinRelayTxFee,
+        // "Dust" is defined in terms of CTransaction::minRelayTxFee,
         // which has units satoshis-per-kilobyte.
         // If you'd pay more than 1/3 in fees
         // to spend something, then we consider it dust.
         // A typical txout is 34 bytes big, and will
-        // need a CTxIn of at least 148 bytes to spend,
+        // need a CTxIn of at least 148 bytes to spend:
         // so dust is a txout less than 546 satoshis 
-        // with default nMinRelayTxFee.
-        return ((nValue*1000)/(3*((int)GetSerializeSize(SER_DISK,0)+148)) < nMinRelayTxFee);
+        // with default minRelayTxFee.
+        size_t nSize = GetSerializeSize(SER_DISK,0)+148u;
+        return (nValue < 3*minRelayTxFee.GetFee(nSize));
     }
 
     friend bool operator==(const CTxOut& a, const CTxOut& b)
@@ -183,8 +206,8 @@ public:
 class CTransaction
 {
 public:
-    static int64_t nMinTxFee;
-    static int64_t nMinRelayTxFee;
+    static CFeeRate minTxFee;
+    static CFeeRate minRelayTxFee;
     static const int CURRENT_VERSION=1;
     int nVersion;
     std::vector<CTxIn> vin;