From fb9c7896c4ab2cf63fe85e8a126f97165f12db43 Mon Sep 17 00:00:00 2001
From: MarcoFalke <falke.marco@gmail.com>
Date: Sun, 3 Apr 2016 13:44:01 +0200
Subject: [PATCH] [amount] Add support for negative fee rates

---
 src/amount.cpp | 22 ++++++++++++++++------
 src/amount.h   | 21 ++++++++++++++-------
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/src/amount.cpp b/src/amount.cpp
index 7de7fa113..99ed48d30 100644
--- a/src/amount.cpp
+++ b/src/amount.cpp
@@ -10,20 +10,30 @@
 
 const std::string CURRENCY_UNIT = "BTC";
 
-CFeeRate::CFeeRate(const CAmount& nFeePaid, size_t nSize)
+CFeeRate::CFeeRate(const CAmount& nFeePaid, size_t nBytes_)
 {
+    assert(nBytes_ <= uint64_t(std::numeric_limits<int64_t>::max()));
+    int64_t nSize = int64_t(nBytes_);
+
     if (nSize > 0)
-        nSatoshisPerK = nFeePaid*1000/nSize;
+        nSatoshisPerK = nFeePaid * 1000 / nSize;
     else
         nSatoshisPerK = 0;
 }
 
-CAmount CFeeRate::GetFee(size_t nSize) const
+CAmount CFeeRate::GetFee(size_t nBytes_) const
 {
-    CAmount nFee = nSatoshisPerK * ceil(1 + nSize / 1000);
+    assert(nBytes_ <= uint64_t(std::numeric_limits<int64_t>::max()));
+    int64_t nSize = int64_t(nBytes_);
 
-    if (nFee == 0 && nSatoshisPerK > 0)
-        nFee = nSatoshisPerK;
+    CAmount nFee = nSatoshisPerK * nSize / 1000;
+
+    if (nFee == 0 && nSize != 0) {
+        if (nSatoshisPerK > 0)
+            nFee = CAmount(1);
+        if (nSatoshisPerK < 0)
+            nFee = CAmount(-1);
+    }
 
     return nFee;
 }
diff --git a/src/amount.h b/src/amount.h
index b42d57511..5d3e7d38e 100644
--- a/src/amount.h
+++ b/src/amount.h
@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <string>
 
+/** Amount in satoshis (Can be negative) */
 typedef int64_t CAmount;
 
 static const CAmount COIN = 100000000;
@@ -30,22 +31,28 @@ extern const std::string CURRENCY_UNIT;
 static const CAmount MAX_MONEY = std::numeric_limits<int64_t>::max();
 inline bool MoneyRange(const CAmount& nValue) { return (nValue >= 0 && nValue <= MAX_MONEY); }
 
-/** Type-safe wrapper class for fee rates
- * (how much to pay based on transaction size)
+/**
+ * Fee rate in satoshis per kilobyte: CAmount / kB
  */
 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) { }
-    CFeeRate(const CAmount& nFeePaid, size_t nSize);
+    /** 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);
     CFeeRate(const CFeeRate& other) { nSatoshisPerK = other.nSatoshisPerK; }
-
-    CAmount GetFee(size_t size) const; // unit returned is satoshis
-    CAmount GetFeePerK() const { return GetFee(1000); } // satoshis-per-1000-bytes
-
+    /**
+     * Return the fee in satoshis for the given size in bytes.
+     */
+    CAmount GetFee(size_t nBytes) const;
+    /**
+     * Return the fee in satoshis for a size of 1000 bytes
+     */
+    CAmount GetFeePerK() const { return GetFee(1000); }
     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; }