1 files changed, 51 insertions, 0 deletions
diff --git a/src/test/DoS_tests.cpp b/src/test/DoS_tests.cpp
index 1093b73d80..01e6691254 100644
--- a/src/test/DoS_tests.cpp
+++ b/src/test/DoS_tests.cpp
@@ -1,6 +1,7 @@
 //
 // Unit tests for denial-of-service detection/prevention code
 //
+#include <boost/assign/list_of.hpp> // for 'map_list_of()'
 #include <boost/test/unit_test.hpp>
 #include <boost/foreach.hpp>
 
@@ -64,4 +65,54 @@ BOOST_AUTO_TEST_CASE(DoS_bantime)
     BOOST_CHECK(!CNode::IsBanned(addr.ip));
 }    
 
+static bool CheckNBits(unsigned int nbits1, int64 time1, unsigned int nbits2, int64 time2)
+{
+    if (time1 > time2)
+        return CheckNBits(nbits2, time2, nbits1, time1);
+    int64 deltaTime = time2-time1;
+
+    CBigNum required;
+    required.SetCompact(ComputeMinWork(nbits1, deltaTime));
+    CBigNum have;
+    have.SetCompact(nbits2);
+    return (have <= required);
+}
+
+BOOST_AUTO_TEST_CASE(DoS_checknbits)
+{
+    using namespace boost::assign; // for 'map_list_of()'
+
+    // Timestamps,nBits from the bitcoin blockchain.
+    // These are the block-chain checkpoint blocks
+    typedef std::map<int64, unsigned int> BlockData;
+    BlockData chainData =
+        map_list_of(1239852051,486604799)(1262749024,486594666)
+        (1279305360,469854461)(1280200847,469830746)(1281678674,469809688)
+        (1296207707,453179945)(1302624061,453036989)(1309640330,437004818)
+        (1313172719,436789733);
+
+    // Make sure CheckNBits considers every combination of block-chain-lock-in-points
+    // "sane":
+    BOOST_FOREACH(const BlockData::value_type& i, chainData)
+    {
+        BOOST_FOREACH(const BlockData::value_type& j, chainData)
+        {
+            BOOST_CHECK(CheckNBits(i.second, i.first, j.second, j.first));
+        }
+    }
+
+    // Test a couple of insane combinations:
+    BlockData::value_type firstcheck = *(chainData.begin());
+    BlockData::value_type lastcheck = *(chainData.rbegin());
+
+    // First checkpoint difficulty at or a while after the last checkpoint time should fail when
+    // compared to last checkpoint
+    BOOST_CHECK(!CheckNBits(firstcheck.second, lastcheck.first+60*10, lastcheck.second, lastcheck.first));
+    BOOST_CHECK(!CheckNBits(firstcheck.second, lastcheck.first+60*60*24*14, lastcheck.second, lastcheck.first));
+
+    // ... but OK if enough time passed for difficulty to adjust downward:
+    BOOST_CHECK(CheckNBits(firstcheck.second, lastcheck.first+60*60*24*365*4, lastcheck.second, lastcheck.first));
+    
+}
+
 BOOST_AUTO_TEST_SUITE_END()