Merge pull request #4076

397668e Deduplicate uint* comparison operator logic (Pieter Wuille)
df9eb5e Move {Get,Set}Compact from bignum to uint256 (Pieter Wuille)
a703150 Add multiplication and division to uint160/uint256 (Pieter Wuille)
4d480c8 Exception instead of assigning 0 in case of wrong vector length (Pieter Wuille)
eb2cbd7 Deduplicate shared code between uint160 and uint256 (Pieter Wuille)

13 files changed, 473 insertions, 508 deletions

diff --git a/src/bignum.h b/src/bignum.h
index 0259338b31..6b77462d83 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -269,71 +269,6 @@ public:
         return vch;
     }
 
-    // The "compact" format is a representation of a whole
-    // number N using an unsigned 32bit number similar to a
-    // floating point format.
-    // The most significant 8 bits are the unsigned exponent of base 256.
-    // This exponent can be thought of as "number of bytes of N".
-    // The lower 23 bits are the mantissa.
-    // Bit number 24 (0x800000) represents the sign of N.
-    // N = (-1^sign) * mantissa * 256^(exponent-3)
-    //
-    // Satoshi's original implementation used BN_bn2mpi() and BN_mpi2bn().
-    // MPI uses the most significant bit of the first byte as sign.
-    // Thus 0x1234560000 is compact (0x05123456)
-    // and  0xc0de000000 is compact (0x0600c0de)
-    // (0x05c0de00) would be -0x40de000000
-    //
-    // Bitcoin only uses this "compact" format for encoding difficulty
-    // targets, which are unsigned 256bit quantities.  Thus, all the
-    // complexities of the sign bit and using base 256 are probably an
-    // implementation accident.
-    //
-    // This implementation directly uses shifts instead of going
-    // through an intermediate MPI representation.
-    CBigNum& SetCompact(unsigned int nCompact)
-    {
-        unsigned int nSize = nCompact >> 24;
-        bool fNegative     =(nCompact & 0x00800000) != 0;
-        unsigned int nWord = nCompact & 0x007fffff;
-        if (nSize <= 3)
-        {
-            nWord >>= 8*(3-nSize);
-            BN_set_word(this, nWord);
-        }
-        else
-        {
-            BN_set_word(this, nWord);
-            BN_lshift(this, this, 8*(nSize-3));
-        }
-        BN_set_negative(this, fNegative);
-        return *this;
-    }
-
-    unsigned int GetCompact() const
-    {
-        unsigned int nSize = BN_num_bytes(this);
-        unsigned int nCompact = 0;
-        if (nSize <= 3)
-            nCompact = BN_get_word(this) << 8*(3-nSize);
-        else
-        {
-            CBigNum bn;
-            BN_rshift(&bn, this, 8*(nSize-3));
-            nCompact = BN_get_word(&bn);
-        }
-        // The 0x00800000 bit denotes the sign.
-        // Thus, if it is already set, divide the mantissa by 256 and increase the exponent.
-        if (nCompact & 0x00800000)
-        {
-            nCompact >>= 8;
-            nSize++;
-        }
-        nCompact |= nSize << 24;
-        nCompact |= (BN_is_negative(this) ? 0x00800000 : 0);
-        return nCompact;
-    }
-
     void SetHex(const std::string& str)
     {
         // skip 0x
diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index eb56800b92..f5cf846a01 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -110,7 +110,7 @@ public:
         vAlertPubKey = ParseHex("04fc9702847840aaf195de8442ebecedf5b095cdbb9bc716bda9110971b28a49e0ead8564ff0db22209e0374782c093bb899692d524e9d6a6956e7c5ecbcd68284");
         nDefaultPort = 8333;
         nRPCPort = 8332;
-        bnProofOfWorkLimit = CBigNum(~uint256(0) >> 32);
+        bnProofOfWorkLimit = ~uint256(0) >> 32;
         nSubsidyHalvingInterval = 210000;
 
         // Build the genesis block. Note that the output of the genesis coinbase cannot
@@ -233,7 +233,7 @@ public:
         pchMessageStart[2] = 0xb5;
         pchMessageStart[3] = 0xda;
         nSubsidyHalvingInterval = 150;
-        bnProofOfWorkLimit = CBigNum(~uint256(0) >> 1);
+        bnProofOfWorkLimit = ~uint256(0) >> 1;
         genesis.nTime = 1296688602;
         genesis.nBits = 0x207fffff;
         genesis.nNonce = 2;
diff --git a/src/chainparams.h b/src/chainparams.h
index 542afeaf92..f3f24efd99 100644
--- a/src/chainparams.h
+++ b/src/chainparams.h
@@ -56,7 +56,7 @@ public:
     const MessageStartChars& MessageStart() const { return pchMessageStart; }
     const vector<unsigned char>& AlertKey() const { return vAlertPubKey; }
     int GetDefaultPort() const { return nDefaultPort; }
-    const CBigNum& ProofOfWorkLimit() const { return bnProofOfWorkLimit; }
+    const uint256& ProofOfWorkLimit() const { return bnProofOfWorkLimit; }
     int SubsidyHalvingInterval() const { return nSubsidyHalvingInterval; }
     virtual const CBlock& GenesisBlock() const = 0;
     virtual bool RequireRPCPassword() const { return true; }
@@ -75,7 +75,7 @@ protected:
     vector<unsigned char> vAlertPubKey;
     int nDefaultPort;
     int nRPCPort;
-    CBigNum bnProofOfWorkLimit;
+    uint256 bnProofOfWorkLimit;
     int nSubsidyHalvingInterval;
     string strDataDir;
     vector<CDNSSeedData> vSeeds;
diff --git a/src/main.cpp b/src/main.cpp
index e384f809bf..379ca3ef74 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1207,13 +1207,13 @@ static const int64_t nInterval = nTargetTimespan / nTargetSpacing;
 //
 unsigned int ComputeMinWork(unsigned int nBase, int64_t nTime)
 {
-    const CBigNum &bnLimit = Params().ProofOfWorkLimit();
+    const uint256 &bnLimit = Params().ProofOfWorkLimit();
     // Testnet has min-difficulty blocks
     // after nTargetSpacing*2 time between blocks:
     if (TestNet() && nTime > nTargetSpacing*2)
         return bnLimit.GetCompact();
 
-    CBigNum bnResult;
+    uint256 bnResult;
     bnResult.SetCompact(nBase);
     while (nTime > 0 && bnResult < bnLimit)
     {
@@ -1272,8 +1272,10 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
         nActualTimespan = nTargetTimespan*4;
 
     // Retarget
-    CBigNum bnNew;
+    uint256 bnNew;
+    uint256 bnOld;
     bnNew.SetCompact(pindexLast->nBits);
+    bnOld = bnNew;
     bnNew *= nActualTimespan;
     bnNew /= nTargetTimespan;
 
@@ -1283,23 +1285,25 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
     /// debug print
     LogPrintf("GetNextWorkRequired RETARGET\n");
     LogPrintf("nTargetTimespan = %d    nActualTimespan = %d\n", nTargetTimespan, nActualTimespan);
-    LogPrintf("Before: %08x  %s\n", pindexLast->nBits, CBigNum().SetCompact(pindexLast->nBits).getuint256().ToString());
-    LogPrintf("After:  %08x  %s\n", bnNew.GetCompact(), bnNew.getuint256().ToString());
+    LogPrintf("Before: %08x  %s\n", pindexLast->nBits, bnOld.ToString());
+    LogPrintf("After:  %08x  %s\n", bnNew.GetCompact(), bnNew.ToString());
 
     return bnNew.GetCompact();
 }
 
 bool CheckProofOfWork(uint256 hash, unsigned int nBits)
 {
-    CBigNum bnTarget;
-    bnTarget.SetCompact(nBits);
+    bool fNegative;
+    bool fOverflow;
+    uint256 bnTarget;
+    bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
 
     // Check range
-    if (bnTarget <= 0 || bnTarget > Params().ProofOfWorkLimit())
+    if (fNegative || bnTarget == 0 || fOverflow || bnTarget > Params().ProofOfWorkLimit())
         return error("CheckProofOfWork() : nBits below minimum work");
 
     // Check proof of work matches claimed amount
-    if (hash > bnTarget.getuint256())
+    if (hash > bnTarget)
         return error("CheckProofOfWork() : hash doesn't match nBits");
 
     return true;
@@ -1338,7 +1342,7 @@ void CheckForkWarningConditions()
     if (pindexBestForkTip && chainActive.Height() - pindexBestForkTip->nHeight >= 72)
         pindexBestForkTip = NULL;
 
-    if (pindexBestForkTip || (pindexBestInvalid && pindexBestInvalid->nChainWork > chainActive.Tip()->nChainWork + (chainActive.Tip()->GetBlockWork() * 6).getuint256()))
+    if (pindexBestForkTip || (pindexBestInvalid && pindexBestInvalid->nChainWork > chainActive.Tip()->nChainWork + (chainActive.Tip()->GetBlockWork() * 6)))
     {
         if (!fLargeWorkForkFound)
         {
@@ -1394,7 +1398,7 @@ void CheckForkWarningConditionsOnNewFork(CBlockIndex* pindexNewForkTip)
     // We define it this way because it allows us to only store the highest fork tip (+ base) which meets
     // the 7-block condition and from this always have the most-likely-to-cause-warning fork
     if (pfork && (!pindexBestForkTip || (pindexBestForkTip && pindexNewForkTip->nHeight > pindexBestForkTip->nHeight)) &&
-            pindexNewForkTip->nChainWork - pfork->nChainWork > (pfork->GetBlockWork() * 7).getuint256() &&
+            pindexNewForkTip->nChainWork - pfork->nChainWork > (pfork->GetBlockWork() * 7) &&
             chainActive.Height() - pindexNewForkTip->nHeight < 72)
     {
         pindexBestForkTip = pindexNewForkTip;
@@ -1428,10 +1432,6 @@ void static InvalidChainFound(CBlockIndex* pindexNew)
     if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
     {
         pindexBestInvalid = pindexNew;
-        // The current code doesn't actually read the BestInvalidWork entry in
-        // the block database anymore, as it is derived from the flags in block
-        // index entry. We only write it for backward compatibility.
-        pblocktree->WriteBestInvalidWork(CBigNum(pindexBestInvalid->nChainWork));
         uiInterface.NotifyBlocksChanged();
     }
     LogPrintf("InvalidChainFound: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n",
@@ -2174,7 +2174,7 @@ CBlockIndex* AddToBlockIndex(CBlockHeader& block)
         pindexNew->pprev = (*miPrev).second;
         pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
     }
-    pindexNew->nChainWork = (pindexNew->pprev ? pindexNew->pprev->nChainWork : 0) + pindexNew->GetBlockWork().getuint256();
+    pindexNew->nChainWork = (pindexNew->pprev ? pindexNew->pprev->nChainWork : 0) + pindexNew->GetBlockWork();
     pindexNew->RaiseValidity(BLOCK_VALID_TREE);
 
     return pindexNew;
@@ -2351,11 +2351,12 @@ bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state, bool f
             return state.DoS(100, error("CheckBlockHeader() : block with timestamp before last checkpoint"),
                              REJECT_CHECKPOINT, "time-too-old");
         }
-        CBigNum bnNewBlock;
-        bnNewBlock.SetCompact(block.nBits);
-        CBigNum bnRequired;
+        bool fOverflow = false;
+        uint256 bnNewBlock;
+        bnNewBlock.SetCompact(block.nBits, NULL, &fOverflow);
+        uint256 bnRequired;
         bnRequired.SetCompact(ComputeMinWork(pcheckpoint->nBits, deltaTime));
-        if (bnNewBlock > bnRequired)
+        if (fOverflow || bnNewBlock > bnRequired)
         {
             return state.DoS(100, error("CheckBlockHeader() : block with too little proof-of-work"),
                              REJECT_INVALID, "bad-diffbits");
@@ -2926,7 +2927,7 @@ bool static LoadBlockIndexDB()
     BOOST_FOREACH(const PAIRTYPE(int, CBlockIndex*)& item, vSortedByHeight)
     {
         CBlockIndex* pindex = item.second;
-        pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + pindex->GetBlockWork().getuint256();
+        pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + pindex->GetBlockWork();
         pindex->nChainTx = (pindex->pprev ? pindex->pprev->nChainTx : 0) + pindex->nTx;
         if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS))
             setBlockIndexValid.insert(pindex);
diff --git a/src/main.h b/src/main.h
index 3d3773138d..f47c9ee825 100644
--- a/src/main.h
+++ b/src/main.h
@@ -10,7 +10,6 @@
 #include "bitcoin-config.h"
 #endif
 
-#include "bignum.h"
 #include "chainparams.h"
 #include "coins.h"
 #include "core.h"
@@ -814,13 +813,19 @@ public:
         return (int64_t)nTime;
     }
 
-    CBigNum GetBlockWork() const
+    uint256 GetBlockWork() const
     {
-        CBigNum bnTarget;
-        bnTarget.SetCompact(nBits);
-        if (bnTarget <= 0)
+        uint256 bnTarget;
+        bool fNegative;
+        bool fOverflow;
+        bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
+        if (fNegative || fOverflow || bnTarget == 0)
             return 0;
-        return (CBigNum(1)<<256) / (bnTarget+1);
+        // We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256
+        // as it's too large for a uint256. However, as 2**256 is at least as large
+        // as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,
+        // or ~bnTarget / (nTarget+1) + 1.
+        return (~bnTarget / (bnTarget + 1)) + 1;
     }
 
     bool CheckIndex() const
diff --git a/src/miner.cpp b/src/miner.cpp
index 01fc56601b..50be4fad40 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -466,7 +466,7 @@ CBlockTemplate* CreateNewBlockWithKey(CReserveKey& reservekey)
 bool CheckWork(CBlock* pblock, CWallet& wallet, CReserveKey& reservekey)
 {
     uint256 hash = pblock->GetHash();
-    uint256 hashTarget = CBigNum().SetCompact(pblock->nBits).getuint256();
+    uint256 hashTarget = uint256().SetCompact(pblock->nBits);
 
     if (hash > hashTarget)
         return false;
@@ -552,7 +552,7 @@ void static BitcoinMiner(CWallet *pwallet)
         // Search
         //
         int64_t nStart = GetTime();
-        uint256 hashTarget = CBigNum().SetCompact(pblock->nBits).getuint256();
+        uint256 hashTarget = uint256().SetCompact(pblock->nBits);
         uint256 hashbuf[2];
         uint256& hash = *alignup<16>(hashbuf);
         while (true)
@@ -636,7 +636,7 @@ void static BitcoinMiner(CWallet *pwallet)
             {
                 // Changing pblock->nTime can change work required on testnet:
                 nBlockBits = ByteReverse(pblock->nBits);
-                hashTarget = CBigNum().SetCompact(pblock->nBits).getuint256();
+                hashTarget.SetCompact(pblock->nBits);
             }
         }
     } }
diff --git a/src/rpcmining.cpp b/src/rpcmining.cpp
index 070cf1cb2a..cb903b585a 100644
--- a/src/rpcmining.cpp
+++ b/src/rpcmining.cpp
@@ -363,7 +363,7 @@ Value getwork(const Array& params, bool fHelp)
         char phash1[64];
         FormatHashBuffers(pblock, pmidstate, pdata, phash1);
 
-        uint256 hashTarget = CBigNum().SetCompact(pblock->nBits).getuint256();
+        uint256 hashTarget = uint256().SetCompact(pblock->nBits);
 
         Object result;
         result.push_back(Pair("midstate", HexStr(BEGIN(pmidstate), END(pmidstate)))); // deprecated
@@ -559,7 +559,7 @@ Value getblocktemplate(const Array& params, bool fHelp)
     Object aux;
     aux.push_back(Pair("flags", HexStr(COINBASE_FLAGS.begin(), COINBASE_FLAGS.end())));
 
-    uint256 hashTarget = CBigNum().SetCompact(pblock->nBits).getuint256();
+    uint256 hashTarget = uint256().SetCompact(pblock->nBits);
 
     static Array aMutable;
     if (aMutable.empty())
diff --git a/src/test/DoS_tests.cpp b/src/test/DoS_tests.cpp
index d86cc7a290..897fb87e46 100644
--- a/src/test/DoS_tests.cpp
+++ b/src/test/DoS_tests.cpp
@@ -106,9 +106,9 @@ static bool CheckNBits(unsigned int nbits1, int64_t time1, unsigned int nbits2,
         return CheckNBits(nbits2, time2, nbits1, time1);
     int64_t deltaTime = time2-time1;
 
-    CBigNum required;
+    uint256 required;
     required.SetCompact(ComputeMinWork(nbits1, deltaTime));
-    CBigNum have;
+    uint256 have;
     have.SetCompact(nbits2);
     return (have <= required);
 }
diff --git a/src/test/bignum_tests.cpp b/src/test/bignum_tests.cpp
index d5ee8c9778..01967c7684 100644
--- a/src/test/bignum_tests.cpp
+++ b/src/test/bignum_tests.cpp
@@ -125,94 +125,6 @@ BOOST_AUTO_TEST_CASE(bignum_setint64)
 }
 
 
-BOOST_AUTO_TEST_CASE(bignum_SetCompact)
-{
-    CBigNum num;
-    num.SetCompact(0);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x00123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x01003456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x02000056);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x03000000);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x04000000);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x00923456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x01803456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x02800056);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x03800000);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-    
-    num.SetCompact(0x04800000);
-    BOOST_CHECK_EQUAL(num.GetHex(), "0");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
-
-    num.SetCompact(0x01123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "12");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x01120000U);
-
-    // Make sure that we don't generate compacts with the 0x00800000 bit set
-    num = 0x80;
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x02008000U);
-
-    num.SetCompact(0x01fedcba);
-    BOOST_CHECK_EQUAL(num.GetHex(), "-7e");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x01fe0000U);
-
-    num.SetCompact(0x02123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "1234");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x02123400U);
-
-    num.SetCompact(0x03123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "123456");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x03123456U);
-
-    num.SetCompact(0x04123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "12345600");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x04123456U);
-
-    num.SetCompact(0x04923456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "-12345600");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x04923456U);
-
-    num.SetCompact(0x05009234);
-    BOOST_CHECK_EQUAL(num.GetHex(), "92340000");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x05009234U);
-
-    num.SetCompact(0x20123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "1234560000000000000000000000000000000000000000000000000000000000");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0x20123456U);
-
-    num.SetCompact(0xff123456);
-    BOOST_CHECK_EQUAL(num.GetHex(), "123456000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000");
-    BOOST_CHECK_EQUAL(num.GetCompact(), 0xff123456U);
-}
-
 BOOST_AUTO_TEST_CASE(bignum_SetHex)
 {
     std::string hexStr = "deecf97fd890808b9cc0f1b6a3e7a60b400f52710e6ad075b1340755bfa58cc9";
diff --git a/src/test/uint256_tests.cpp b/src/test/uint256_tests.cpp
index 815babf107..4b1a2ae58f 100644
--- a/src/test/uint256_tests.cpp
+++ b/src/test/uint256_tests.cpp
@@ -160,11 +160,11 @@ BOOST_AUTO_TEST_CASE( basics ) // constructors, equality, inequality
     tmpS = ~R2S; BOOST_CHECK(tmpS == ~R2S);
     tmpS = ~MaxS; BOOST_CHECK(tmpS == ~MaxS);
 
-    // Wrong length must give 0
-    BOOST_CHECK(uint256(std::vector<unsigned char>(OneArray,OneArray+31)) == 0);
-    BOOST_CHECK(uint256(std::vector<unsigned char>(OneArray,OneArray+20)) == 0);
-    BOOST_CHECK(uint160(std::vector<unsigned char>(OneArray,OneArray+32)) == 0);
-    BOOST_CHECK(uint160(std::vector<unsigned char>(OneArray,OneArray+19)) == 0);
+    // Wrong length must throw exception.
+    BOOST_CHECK_THROW(uint256(std::vector<unsigned char>(OneArray,OneArray+31)), uint_error);
+    BOOST_CHECK_THROW(uint256(std::vector<unsigned char>(OneArray,OneArray+20)), uint_error);
+    BOOST_CHECK_THROW(uint160(std::vector<unsigned char>(OneArray,OneArray+32)), uint_error);
+    BOOST_CHECK_THROW(uint160(std::vector<unsigned char>(OneArray,OneArray+19)), uint_error);
 }
 
 void shiftArrayRight(unsigned char* to, const unsigned char* from, unsigned int arrayLength, unsigned int bitsToShift) 
@@ -482,6 +482,77 @@ BOOST_AUTO_TEST_CASE( plusMinus )
 
 }
 
+BOOST_AUTO_TEST_CASE( multiply )
+{
+    BOOST_CHECK((R1L * R1L).ToString() == "62a38c0486f01e45879d7910a7761bf30d5237e9873f9bff3642a732c4d84f10");
+    BOOST_CHECK((R1L * R2L).ToString() == "de37805e9986996cfba76ff6ba51c008df851987d9dd323f0e5de07760529c40");
+    BOOST_CHECK((R1L * ZeroL) == ZeroL);
+    BOOST_CHECK((R1L * OneL) == R1L);
+    BOOST_CHECK((R1L * MaxL) == -R1L);
+    BOOST_CHECK((R2L * R1L) == (R1L * R2L));
+    BOOST_CHECK((R2L * R2L).ToString() == "ac8c010096767d3cae5005dec28bb2b45a1d85ab7996ccd3e102a650f74ff100");
+    BOOST_CHECK((R2L * ZeroL) == ZeroL);
+    BOOST_CHECK((R2L * OneL) == R2L);
+    BOOST_CHECK((R2L * MaxL) == -R2L);
+
+    BOOST_CHECK((R1S * R1S).ToString() == "a7761bf30d5237e9873f9bff3642a732c4d84f10");
+    BOOST_CHECK((R1S * R2S).ToString() == "ba51c008df851987d9dd323f0e5de07760529c40");
+    BOOST_CHECK((R1S * ZeroS) == ZeroS);
+    BOOST_CHECK((R1S * OneS) == R1S);
+    BOOST_CHECK((R1S * MaxS) == -R1S);
+    BOOST_CHECK((R2S * R1S) == (R1S * R2S));
+    BOOST_CHECK((R2S * R2S).ToString() == "c28bb2b45a1d85ab7996ccd3e102a650f74ff100");
+    BOOST_CHECK((R2S * ZeroS) == ZeroS);
+    BOOST_CHECK((R2S * OneS) == R2S);
+    BOOST_CHECK((R2S * MaxS) == -R2S);
+
+    BOOST_CHECK(MaxL * MaxL == OneL);
+    BOOST_CHECK(MaxS * MaxS == OneS);
+
+    BOOST_CHECK((R1L * 0) == 0);
+    BOOST_CHECK((R1L * 1) == R1L);
+    BOOST_CHECK((R1L * 3).ToString() == "7759b1c0ed14047f961ad09b20ff83687876a0181a367b813634046f91def7d4");
+    BOOST_CHECK((R2L * 0x87654321UL).ToString() == "23f7816e30c4ae2017257b7a0fa64d60402f5234d46e746b61c960d09a26d070");
+    BOOST_CHECK((R1S * 0) == 0);
+    BOOST_CHECK((R1S * 1) == R1S);
+    BOOST_CHECK((R1S * 7).ToString() == "f7a987f3c3bf758d927f202d7e795faeff084244");
+    BOOST_CHECK((R2S * 0xFFFFFFFFUL).ToString() == "1c6f6c930353e17f7d6127213bb18d2883e2cd90");
+}
+
+BOOST_AUTO_TEST_CASE( divide )
+{
+    uint256 D1L("AD7133AC1977FA2B7");
+    uint256 D2L("ECD751716");
+    BOOST_CHECK((R1L / D1L).ToString() == "00000000000000000b8ac01106981635d9ed112290f8895545a7654dde28fb3a");
+    BOOST_CHECK((R1L / D2L).ToString() == "000000000873ce8efec5b67150bad3aa8c5fcb70e947586153bf2cec7c37c57a");
+    BOOST_CHECK(R1L / OneL == R1L);
+    BOOST_CHECK(R1L / MaxL == ZeroL);
+    BOOST_CHECK(MaxL / R1L == 2);
+    BOOST_CHECK_THROW(R1L / ZeroL, uint_error);
+    BOOST_CHECK((R2L / D1L).ToString() == "000000000000000013e1665895a1cc981de6d93670105a6b3ec3b73141b3a3c5");
+    BOOST_CHECK((R2L / D2L).ToString() == "000000000e8f0abe753bb0afe2e9437ee85d280be60882cf0bd1aaf7fa3cc2c4");
+    BOOST_CHECK(R2L / OneL == R2L);
+    BOOST_CHECK(R2L / MaxL == ZeroL);
+    BOOST_CHECK(MaxL / R2L == 1);
+    BOOST_CHECK_THROW(R2L / ZeroL, uint_error);
+
+    uint160 D1S("D3C5EDCDEA54EB92679F0A4B4");
+    uint160 D2S("13037");
+    BOOST_CHECK((R1S / D1S).ToString() == "0000000000000000000000000db9af3beade6c02");
+    BOOST_CHECK((R1S / D2S).ToString() == "000098dfb6cc40ca592bf74366794f298ada205c");
+    BOOST_CHECK(R1S / OneS == R1S);
+    BOOST_CHECK(R1S / MaxS == ZeroS);
+    BOOST_CHECK(MaxS / R1S == 1);
+    BOOST_CHECK_THROW(R1S / ZeroS, uint_error);
+    BOOST_CHECK((R2S / D1S).ToString() == "0000000000000000000000000c5608e781182047");
+    BOOST_CHECK((R2S / D2S).ToString() == "00008966751b7187c3c67c1fda5cea7db2c1c069");
+    BOOST_CHECK(R2S / OneS == R2S);
+    BOOST_CHECK(R2S / MaxS == ZeroS);
+    BOOST_CHECK(MaxS / R2S == 1);
+    BOOST_CHECK_THROW(R2S / ZeroS, uint_error);
+}
+
+
 bool almostEqual(double d1, double d2) 
 {
     return fabs(d1-d2) <= 4*fabs(d1)*std::numeric_limits<double>::epsilon();
@@ -604,6 +675,135 @@ BOOST_AUTO_TEST_CASE( methods ) // GetHex SetHex begin() end() size() GetLow64 G
     }
 }
 
+BOOST_AUTO_TEST_CASE(bignum_SetCompact)
+{
+    uint256 num;
+    bool fNegative;
+    bool fOverflow;
+    num.SetCompact(0, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x00123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x01003456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x02000056, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x03000000, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x04000000, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x00923456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x01803456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x02800056, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x03800000, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x04800000, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x01123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000000012");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x01120000U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    // Make sure that we don't generate compacts with the 0x00800000 bit set
+    num = 0x80;
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x02008000U);
+
+    num.SetCompact(0x01fedcba, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "000000000000000000000000000000000000000000000000000000000000007e");
+    BOOST_CHECK_EQUAL(num.GetCompact(true), 0x01fe0000U);
+    BOOST_CHECK_EQUAL(fNegative, true);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x02123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000001234");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x02123400U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x03123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000000123456");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x03123456U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x04123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000012345600");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x04123456U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x04923456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000012345600");
+    BOOST_CHECK_EQUAL(num.GetCompact(true), 0x04923456U);
+    BOOST_CHECK_EQUAL(fNegative, true);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x05009234, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "0000000000000000000000000000000000000000000000000000000092340000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x05009234U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0x20123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(num.GetHex(), "1234560000000000000000000000000000000000000000000000000000000000");
+    BOOST_CHECK_EQUAL(num.GetCompact(), 0x20123456U);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, false);
+
+    num.SetCompact(0xff123456, &fNegative, &fOverflow);
+    BOOST_CHECK_EQUAL(fNegative, false);
+    BOOST_CHECK_EQUAL(fOverflow, true);
+}
+
+
 BOOST_AUTO_TEST_CASE( getmaxcoverage ) // some more tests just to get 100% coverage
 {
     // ~R1L give a base_uint<256>
diff --git a/src/txdb.cpp b/src/txdb.cpp
index cb92922a35..4eab8525a5 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -73,12 +73,6 @@ bool CBlockTreeDB::WriteBlockIndex(const CDiskBlockIndex& blockindex)
     return Write(make_pair('b', blockindex.GetBlockHash()), blockindex);
 }
 
-bool CBlockTreeDB::WriteBestInvalidWork(const CBigNum& bnBestInvalidWork)
-{
-    // Obsolete; only written for backward compatibility.
-    return Write('I', bnBestInvalidWork);
-}
-
 bool CBlockTreeDB::WriteBlockFileInfo(int nFile, const CBlockFileInfo &info) {
     return Write(make_pair('f', nFile), info);
 }
diff --git a/src/txdb.h b/src/txdb.h
index 5eb5731db3..7257b0dd21 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -14,7 +14,6 @@
 #include <utility>
 #include <vector>
 
-class CBigNum;
 class CCoins;
 class uint256;
 
@@ -52,7 +51,6 @@ private:
     void operator=(const CBlockTreeDB&);
 public:
     bool WriteBlockIndex(const CDiskBlockIndex& blockindex);
-    bool WriteBestInvalidWork(const CBigNum& bnBestInvalidWork);
     bool ReadBlockFileInfo(int nFile, CBlockFileInfo &fileinfo);
     bool WriteBlockFileInfo(int nFile, const CBlockFileInfo &fileinfo);
     bool ReadLastBlockFile(int &nFile);
diff --git a/src/uint256.h b/src/uint256.h
index ba903bc8fc..1acedd14bf 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -1,11 +1,13 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2013 The Bitcoin developers
+// Copyright (c) 2009-2014 The Bitcoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #ifndef BITCOIN_UINT256_H
 #define BITCOIN_UINT256_H
 
+#include <assert.h>
+#include <stdexcept>
 #include <stdint.h>
 #include <stdio.h>
 #include <string>
@@ -19,17 +21,59 @@ inline signed char HexDigit(char c)
     return p_util_hexdigit[(unsigned char)c];
 }
 
-/** Base class without constructors for uint256 and uint160.
- * This makes the compiler let you use it in a union.
- */
+class uint_error : public std::runtime_error {
+public:
+    explicit uint_error(const std::string& str) : std::runtime_error(str) {}
+};
+
+/** Template base class for unsigned big integers. */
 template<unsigned int BITS>
 class base_uint
 {
-protected:
+private:
     enum { WIDTH=BITS/32 };
     uint32_t pn[WIDTH];
 public:
 
+    base_uint()
+    {
+        for (int i = 0; i < WIDTH; i++)
+            pn[i] = 0;
+    }
+
+    base_uint(const base_uint& b)
+    {
+        for (int i = 0; i < WIDTH; i++)
+            pn[i] = b.pn[i];
+    }
+
+    base_uint& operator=(const base_uint& b)
+    {
+        for (int i = 0; i < WIDTH; i++)
+            pn[i] = b.pn[i];
+        return *this;
+    }
+
+    base_uint(uint64_t b)
+    {
+        pn[0] = (unsigned int)b;
+        pn[1] = (unsigned int)(b >> 32);
+        for (int i = 2; i < WIDTH; i++)
+            pn[i] = 0;
+    }
+
+    explicit base_uint(const std::string& str)
+    {
+        SetHex(str);
+    }
+
+    explicit base_uint(const std::vector<unsigned char>& vch)
+    {
+        if (vch.size() != sizeof(pn))
+            throw uint_error("Converting vector of wrong size to base_uint");
+        memcpy(pn, &vch[0], sizeof(pn));
+    }
+
     bool operator!() const
     {
         for (int i = 0; i < WIDTH; i++)
@@ -178,6 +222,57 @@ public:
         return *this;
     }
 
+    base_uint& operator*=(uint32_t b32)
+    {
+        uint64_t carry = 0;
+        for (int i = 0; i < WIDTH; i++)
+        {
+            uint64_t n = carry + (uint64_t)b32 * pn[i];
+            pn[i] = n & 0xffffffff;
+            carry = n >> 32;
+        }
+        return *this;
+    }
+
+    base_uint& operator*=(const base_uint& b)
+    {
+        base_uint a = *this;
+        *this = 0;
+        for (int j = 0; j < WIDTH; j++) {
+            uint64_t carry = 0;
+            for (int i = 0; i + j < WIDTH; i++) {
+                uint64_t n = carry + pn[i + j] + (uint64_t)a.pn[j] * b.pn[i];
+                pn[i + j] = n & 0xffffffff;
+                carry = n >> 32;
+            }
+        }
+        return *this;
+    }
+
+    base_uint& operator/=(const base_uint& b)
+    {
+        base_uint div = b; // make a copy, so we can shift.
+        base_uint num = *this; // make a copy, so we can subtract.
+        *this = 0; // the quotient.
+        int num_bits = num.bits();
+        int div_bits = div.bits();
+        if (div_bits == 0)
+            throw uint_error("Division by zero");
+        if (div_bits > num_bits) // the result is certainly 0.
+            return *this;
+        int shift = num_bits - div_bits;
+        div <<= shift; // shift so that div and nun align.
+        while (shift >= 0) {
+            if (num >= div) {
+                num -= div;
+                pn[shift / 32] |= (1 << (shift & 31)); // set a bit of the result.
+            }
+            div >>= 1; // shift back.
+            shift--;
+        }
+        // num now contains the remainder of the division.
+        return *this;
+    }
 
     base_uint& operator++()
     {
@@ -213,86 +308,46 @@ public:
         return ret;
     }
 
-
-    friend inline bool operator<(const base_uint& a, const base_uint& b)
-    {
-        for (int i = base_uint::WIDTH-1; i >= 0; i--)
-        {
-            if (a.pn[i] < b.pn[i])
-                return true;
-            else if (a.pn[i] > b.pn[i])
-                return false;
-        }
-        return false;
-    }
-
-    friend inline bool operator<=(const base_uint& a, const base_uint& b)
-    {
-        for (int i = base_uint::WIDTH-1; i >= 0; i--)
-        {
-            if (a.pn[i] < b.pn[i])
-                return true;
-            else if (a.pn[i] > b.pn[i])
-                return false;
+    int CompareTo(const base_uint& b) const {
+        for (int i = base_uint::WIDTH-1; i >= 0; i--) {
+            if (pn[i] < b.pn[i])
+                return -1;
+            if (pn[i] > b.pn[i])
+                return 1;
         }
-        return true;
+        return 0;
     }
 
-    friend inline bool operator>(const base_uint& a, const base_uint& b)
-    {
-        for (int i = base_uint::WIDTH-1; i >= 0; i--)
-        {
-            if (a.pn[i] > b.pn[i])
-                return true;
-            else if (a.pn[i] < b.pn[i])
+    bool EqualTo(uint64_t b) const {
+        for (int i = base_uint::WIDTH-1; i >= 2; i--) {
+            if (pn[i])
                 return false;
         }
-        return false;
-    }
-
-    friend inline bool operator>=(const base_uint& a, const base_uint& b)
-    {
-        for (int i = base_uint::WIDTH-1; i >= 0; i--)
-        {
-            if (a.pn[i] > b.pn[i])
-                return true;
-            else if (a.pn[i] < b.pn[i])
-                return false;
-        }
-        return true;
-    }
-
-    friend inline bool operator==(const base_uint& a, const base_uint& b)
-    {
-        for (int i = 0; i < base_uint::WIDTH; i++)
-            if (a.pn[i] != b.pn[i])
-                return false;
-        return true;
-    }
-
-    friend inline bool operator==(const base_uint& a, uint64_t b)
-    {
-        if (a.pn[0] != (unsigned int)b)
+        if (pn[1] != (b >> 32))
             return false;
-        if (a.pn[1] != (unsigned int)(b >> 32))
+        if (pn[0] != (b & 0xfffffffful))
             return false;
-        for (int i = 2; i < base_uint::WIDTH; i++)
-            if (a.pn[i] != 0)
-                return false;
         return true;
     }
 
-    friend inline bool operator!=(const base_uint& a, const base_uint& b)
-    {
-        return (!(a == b));
-    }
-
-    friend inline bool operator!=(const base_uint& a, uint64_t b)
-    {
-        return (!(a == b));
-    }
-
-
+    friend inline const base_uint operator+(const base_uint& a, const base_uint& b) { return base_uint(a) += b; }
+    friend inline const base_uint operator-(const base_uint& a, const base_uint& b) { return base_uint(a) -= b; }
+    friend inline const base_uint operator*(const base_uint& a, const base_uint& b) { return base_uint(a) *= b; }
+    friend inline const base_uint operator/(const base_uint& a, const base_uint& b) { return base_uint(a) /= b; }
+    friend inline const base_uint operator|(const base_uint& a, const base_uint& b) { return base_uint(a) |= b; }
+    friend inline const base_uint operator&(const base_uint& a, const base_uint& b) { return base_uint(a) &= b; }
+    friend inline const base_uint operator^(const base_uint& a, const base_uint& b) { return base_uint(a) ^= b; }
+    friend inline const base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
+    friend inline const base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
+    friend inline const base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
+    friend inline bool operator==(const base_uint& a, const base_uint& b) { return a.CompareTo(b) == 0; }
+    friend inline bool operator!=(const base_uint& a, const base_uint& b) { return a.CompareTo(b) != 0; }
+    friend inline bool operator>(const base_uint& a, const base_uint& b) { return a.CompareTo(b) > 0; }
+    friend inline bool operator<(const base_uint& a, const base_uint& b) { return a.CompareTo(b) < 0; }
+    friend inline bool operator>=(const base_uint& a, const base_uint& b) { return a.CompareTo(b) >= 0; }
+    friend inline bool operator<=(const base_uint& a, const base_uint& b) { return a.CompareTo(b) <= 0; }
+    friend inline bool operator==(const base_uint& a, uint64_t b) { return a.EqualTo(b); }
+    friend inline bool operator!=(const base_uint& a, uint64_t b) { return !a.EqualTo(b); }
 
     std::string GetHex() const
     {
@@ -367,269 +422,134 @@ public:
         return sizeof(pn);
     }
 
+    // Returns the position of the highest bit set plus one, or zero if the
+    // value is zero.
+    unsigned int bits() const
+    {
+        for (int pos = WIDTH-1; pos >= 0; pos--) {
+            if (pn[pos]) {
+                for (int bits = 31; bits > 0; bits--) {
+                    if (pn[pos] & 1<<bits)
+                        return 32*pos + bits + 1;
+                }
+                return 32*pos + 1;
+            }
+        }
+        return 0;
+    }
+
     uint64_t GetLow64() const
     {
         assert(WIDTH >= 2);
         return pn[0] | (uint64_t)pn[1] << 32;
     }
 
-//    unsigned int GetSerializeSize(int nType=0, int nVersion=PROTOCOL_VERSION) const
     unsigned int GetSerializeSize(int nType, int nVersion) const
     {
         return sizeof(pn);
     }
 
     template<typename Stream>
-//    void Serialize(Stream& s, int nType=0, int nVersion=PROTOCOL_VERSION) const
     void Serialize(Stream& s, int nType, int nVersion) const
     {
         s.write((char*)pn, sizeof(pn));
     }
 
     template<typename Stream>
-//    void Unserialize(Stream& s, int nType=0, int nVersion=PROTOCOL_VERSION)
     void Unserialize(Stream& s, int nType, int nVersion)
     {
         s.read((char*)pn, sizeof(pn));
     }
-
-
-    friend class uint160;
-    friend class uint256;
 };
 
-typedef base_uint<160> base_uint160;
-typedef base_uint<256> base_uint256;
-
-
-
-//
-// uint160 and uint256 could be implemented as templates, but to keep
-// compile errors and debugging cleaner, they're copy and pasted.
-//
-
-
-
-//////////////////////////////////////////////////////////////////////////////
-//
-// uint160
-//
-
-/** 160-bit unsigned integer */
-class uint160 : public base_uint160
-{
+/** 160-bit unsigned big integer. */
+class uint160 : public base_uint<160> {
 public:
-    typedef base_uint160 basetype;
-
-    uint160()
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = 0;
-    }
-
-    uint160(const basetype& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-    }
-
-    uint160& operator=(const basetype& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-        return *this;
-    }
-
-    uint160(uint64_t b)
-    {
-        pn[0] = (unsigned int)b;
-        pn[1] = (unsigned int)(b >> 32);
-        for (int i = 2; i < WIDTH; i++)
-            pn[i] = 0;
-    }
-
-    uint160& operator=(uint64_t b)
-    {
-        pn[0] = (unsigned int)b;
-        pn[1] = (unsigned int)(b >> 32);
-        for (int i = 2; i < WIDTH; i++)
-            pn[i] = 0;
-        return *this;
-    }
-
-    explicit uint160(const std::string& str)
-    {
-        SetHex(str);
-    }
-
-    explicit uint160(const std::vector<unsigned char>& vch)
-    {
-        if (vch.size() == sizeof(pn))
-            memcpy(pn, &vch[0], sizeof(pn));
-        else
-            *this = 0;
-    }
+    uint160() {}
+    uint160(const base_uint<160>& b) : base_uint<160>(b) {}
+    uint160(uint64_t b) : base_uint<160>(b) {}
+    explicit uint160(const std::string& str) : base_uint<160>(str) {}
+    explicit uint160(const std::vector<unsigned char>& vch) : base_uint<160>(vch) {}
 };
 
-inline bool operator==(const uint160& a, uint64_t b)                         { return (base_uint160)a == b; }
-inline bool operator!=(const uint160& a, uint64_t b)                         { return (base_uint160)a != b; }
-inline const uint160 operator<<(const base_uint160& a, unsigned int shift)   { return uint160(a) <<= shift; }
-inline const uint160 operator>>(const base_uint160& a, unsigned int shift)   { return uint160(a) >>= shift; }
-inline const uint160 operator<<(const uint160& a, unsigned int shift)        { return uint160(a) <<= shift; }
-inline const uint160 operator>>(const uint160& a, unsigned int shift)        { return uint160(a) >>= shift; }
-
-inline const uint160 operator^(const base_uint160& a, const base_uint160& b) { return uint160(a) ^= b; }
-inline const uint160 operator&(const base_uint160& a, const base_uint160& b) { return uint160(a) &= b; }
-inline const uint160 operator|(const base_uint160& a, const base_uint160& b) { return uint160(a) |= b; }
-inline const uint160 operator+(const base_uint160& a, const base_uint160& b) { return uint160(a) += b; }
-inline const uint160 operator-(const base_uint160& a, const base_uint160& b) { return uint160(a) -= b; }
-
-inline bool operator<(const base_uint160& a, const uint160& b)               { return (base_uint160)a <  (base_uint160)b; }
-inline bool operator<=(const base_uint160& a, const uint160& b)              { return (base_uint160)a <= (base_uint160)b; }
-inline bool operator>(const base_uint160& a, const uint160& b)               { return (base_uint160)a >  (base_uint160)b; }
-inline bool operator>=(const base_uint160& a, const uint160& b)              { return (base_uint160)a >= (base_uint160)b; }
-inline bool operator==(const base_uint160& a, const uint160& b)              { return (base_uint160)a == (base_uint160)b; }
-inline bool operator!=(const base_uint160& a, const uint160& b)              { return (base_uint160)a != (base_uint160)b; }
-inline const uint160 operator^(const base_uint160& a, const uint160& b)      { return (base_uint160)a ^  (base_uint160)b; }
-inline const uint160 operator&(const base_uint160& a, const uint160& b)      { return (base_uint160)a &  (base_uint160)b; }
-inline const uint160 operator|(const base_uint160& a, const uint160& b)      { return (base_uint160)a |  (base_uint160)b; }
-inline const uint160 operator+(const base_uint160& a, const uint160& b)      { return (base_uint160)a +  (base_uint160)b; }
-inline const uint160 operator-(const base_uint160& a, const uint160& b)      { return (base_uint160)a -  (base_uint160)b; }
-
-inline bool operator<(const uint160& a, const base_uint160& b)               { return (base_uint160)a <  (base_uint160)b; }
-inline bool operator<=(const uint160& a, const base_uint160& b)              { return (base_uint160)a <= (base_uint160)b; }
-inline bool operator>(const uint160& a, const base_uint160& b)               { return (base_uint160)a >  (base_uint160)b; }
-inline bool operator>=(const uint160& a, const base_uint160& b)              { return (base_uint160)a >= (base_uint160)b; }
-inline bool operator==(const uint160& a, const base_uint160& b)              { return (base_uint160)a == (base_uint160)b; }
-inline bool operator!=(const uint160& a, const base_uint160& b)              { return (base_uint160)a != (base_uint160)b; }
-inline const uint160 operator^(const uint160& a, const base_uint160& b)      { return (base_uint160)a ^  (base_uint160)b; }
-inline const uint160 operator&(const uint160& a, const base_uint160& b)      { return (base_uint160)a &  (base_uint160)b; }
-inline const uint160 operator|(const uint160& a, const base_uint160& b)      { return (base_uint160)a |  (base_uint160)b; }
-inline const uint160 operator+(const uint160& a, const base_uint160& b)      { return (base_uint160)a +  (base_uint160)b; }
-inline const uint160 operator-(const uint160& a, const base_uint160& b)      { return (base_uint160)a -  (base_uint160)b; }
-
-inline bool operator<(const uint160& a, const uint160& b)                    { return (base_uint160)a <  (base_uint160)b; }
-inline bool operator<=(const uint160& a, const uint160& b)                   { return (base_uint160)a <= (base_uint160)b; }
-inline bool operator>(const uint160& a, const uint160& b)                    { return (base_uint160)a >  (base_uint160)b; }
-inline bool operator>=(const uint160& a, const uint160& b)                   { return (base_uint160)a >= (base_uint160)b; }
-inline bool operator==(const uint160& a, const uint160& b)                   { return (base_uint160)a == (base_uint160)b; }
-inline bool operator!=(const uint160& a, const uint160& b)                   { return (base_uint160)a != (base_uint160)b; }
-inline const uint160 operator^(const uint160& a, const uint160& b)           { return (base_uint160)a ^  (base_uint160)b; }
-inline const uint160 operator&(const uint160& a, const uint160& b)           { return (base_uint160)a &  (base_uint160)b; }
-inline const uint160 operator|(const uint160& a, const uint160& b)           { return (base_uint160)a |  (base_uint160)b; }
-inline const uint160 operator+(const uint160& a, const uint160& b)           { return (base_uint160)a +  (base_uint160)b; }
-inline const uint160 operator-(const uint160& a, const uint160& b)           { return (base_uint160)a -  (base_uint160)b; }
-
-
-
-//////////////////////////////////////////////////////////////////////////////
-//
-// uint256
-//
-
-/** 256-bit unsigned integer */
-class uint256 : public base_uint256
-{
+/** 256-bit unsigned big integer. */
+class uint256 : public base_uint<256> {
 public:
-    typedef base_uint256 basetype;
-
-    uint256()
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = 0;
-    }
-
-    uint256(const basetype& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-    }
-
-    uint256& operator=(const basetype& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-        return *this;
-    }
-
-    uint256(uint64_t b)
-    {
-        pn[0] = (unsigned int)b;
-        pn[1] = (unsigned int)(b >> 32);
-        for (int i = 2; i < WIDTH; i++)
-            pn[i] = 0;
-    }
-
-    uint256& operator=(uint64_t b)
-    {
-        pn[0] = (unsigned int)b;
-        pn[1] = (unsigned int)(b >> 32);
-        for (int i = 2; i < WIDTH; i++)
-            pn[i] = 0;
+    uint256() {}
+    uint256(const base_uint<256>& b) : base_uint<256>(b) {}
+    uint256(uint64_t b) : base_uint<256>(b) {}
+    explicit uint256(const std::string& str) : base_uint<256>(str) {}
+    explicit uint256(const std::vector<unsigned char>& vch) : base_uint<256>(vch) {}
+
+    // The "compact" format is a representation of a whole
+    // number N using an unsigned 32bit number similar to a
+    // floating point format.
+    // The most significant 8 bits are the unsigned exponent of base 256.
+    // This exponent can be thought of as "number of bytes of N".
+    // The lower 23 bits are the mantissa.
+    // Bit number 24 (0x800000) represents the sign of N.
+    // N = (-1^sign) * mantissa * 256^(exponent-3)
+    //
+    // Satoshi's original implementation used BN_bn2mpi() and BN_mpi2bn().
+    // MPI uses the most significant bit of the first byte as sign.
+    // Thus 0x1234560000 is compact (0x05123456)
+    // and  0xc0de000000 is compact (0x0600c0de)
+    // (0x05c0de00) would be -0x40de000000
+    //
+    // Bitcoin only uses this "compact" format for encoding difficulty
+    // targets, which are unsigned 256bit quantities.  Thus, all the
+    // complexities of the sign bit and using base 256 are probably an
+    // implementation accident.
+    //
+    // This implementation directly uses shifts instead of going
+    // through an intermediate MPI representation.
+    uint256& SetCompact(uint32_t nCompact, bool *pfNegative = NULL, bool *pfOverflow = NULL)
+    {
+        int nSize = nCompact >> 24;
+        uint32_t nWord = nCompact & 0x007fffff;
+        if (nSize <= 3)
+        {
+            nWord >>= 8*(3-nSize);
+            *this = nWord;
+        }
+        else
+        {
+            *this = nWord;
+            *this <<= 8*(nSize-3);
+        }
+        if (pfNegative)
+            *pfNegative = nWord != 0 && (nCompact & 0x00800000) != 0;
+        if (pfOverflow)
+            *pfOverflow = nWord != 0 && ((nSize > 34) ||
+                                         (nWord > 0xff && nSize > 33) ||
+                                         (nWord > 0xffff && nSize > 32));
         return *this;
     }
 
-    explicit uint256(const std::string& str)
-    {
-        SetHex(str);
-    }
-
-    explicit uint256(const std::vector<unsigned char>& vch)
+    uint32_t GetCompact(bool fNegative = false) const
     {
-        if (vch.size() == sizeof(pn))
-            memcpy(pn, &vch[0], sizeof(pn));
+        int nSize = (bits() + 7) / 8;
+        uint32_t nCompact = 0;
+        if (nSize <= 3)
+            nCompact = GetLow64() << 8*(3-nSize);
         else
-            *this = 0;
+        {
+            uint256 bn = *this >> 8*(nSize-3);
+            nCompact = bn.GetLow64();
+        }
+        // The 0x00800000 bit denotes the sign.
+        // Thus, if it is already set, divide the mantissa by 256 and increase the exponent.
+        if (nCompact & 0x00800000)
+        {
+            nCompact >>= 8;
+            nSize++;
+        }
+        assert((nCompact & ~0x007fffff) == 0);
+        assert(nSize < 256);
+        nCompact |= nSize << 24;
+        nCompact |= (fNegative && (nCompact & 0x007fffff) ? 0x00800000 : 0);
+        return nCompact;
     }
 };
 
-inline bool operator==(const uint256& a, uint64_t b)                          { return (base_uint256)a == b; }
-inline bool operator!=(const uint256& a, uint64_t b)                          { return (base_uint256)a != b; }
-inline const uint256 operator<<(const base_uint256& a, unsigned int shift)   { return uint256(a) <<= shift; }
-inline const uint256 operator>>(const base_uint256& a, unsigned int shift)   { return uint256(a) >>= shift; }
-inline const uint256 operator<<(const uint256& a, unsigned int shift)        { return uint256(a) <<= shift; }
-inline const uint256 operator>>(const uint256& a, unsigned int shift)        { return uint256(a) >>= shift; }
-
-inline const uint256 operator^(const base_uint256& a, const base_uint256& b) { return uint256(a) ^= b; }
-inline const uint256 operator&(const base_uint256& a, const base_uint256& b) { return uint256(a) &= b; }
-inline const uint256 operator|(const base_uint256& a, const base_uint256& b) { return uint256(a) |= b; }
-inline const uint256 operator+(const base_uint256& a, const base_uint256& b) { return uint256(a) += b; }
-inline const uint256 operator-(const base_uint256& a, const base_uint256& b) { return uint256(a) -= b; }
-
-inline bool operator<(const base_uint256& a, const uint256& b)          { return (base_uint256)a <  (base_uint256)b; }
-inline bool operator<=(const base_uint256& a, const uint256& b)         { return (base_uint256)a <= (base_uint256)b; }
-inline bool operator>(const base_uint256& a, const uint256& b)          { return (base_uint256)a >  (base_uint256)b; }
-inline bool operator>=(const base_uint256& a, const uint256& b)         { return (base_uint256)a >= (base_uint256)b; }
-inline bool operator==(const base_uint256& a, const uint256& b)         { return (base_uint256)a == (base_uint256)b; }
-inline bool operator!=(const base_uint256& a, const uint256& b)         { return (base_uint256)a != (base_uint256)b; }
-inline const uint256 operator^(const base_uint256& a, const uint256& b) { return (base_uint256)a ^  (base_uint256)b; }
-inline const uint256 operator&(const base_uint256& a, const uint256& b) { return (base_uint256)a &  (base_uint256)b; }
-inline const uint256 operator|(const base_uint256& a, const uint256& b) { return (base_uint256)a |  (base_uint256)b; }
-inline const uint256 operator+(const base_uint256& a, const uint256& b) { return (base_uint256)a +  (base_uint256)b; }
-inline const uint256 operator-(const base_uint256& a, const uint256& b) { return (base_uint256)a -  (base_uint256)b; }
-
-inline bool operator<(const uint256& a, const base_uint256& b)          { return (base_uint256)a <  (base_uint256)b; }
-inline bool operator<=(const uint256& a, const base_uint256& b)         { return (base_uint256)a <= (base_uint256)b; }
-inline bool operator>(const uint256& a, const base_uint256& b)          { return (base_uint256)a >  (base_uint256)b; }
-inline bool operator>=(const uint256& a, const base_uint256& b)         { return (base_uint256)a >= (base_uint256)b; }
-inline bool operator==(const uint256& a, const base_uint256& b)         { return (base_uint256)a == (base_uint256)b; }
-inline bool operator!=(const uint256& a, const base_uint256& b)         { return (base_uint256)a != (base_uint256)b; }
-inline const uint256 operator^(const uint256& a, const base_uint256& b) { return (base_uint256)a ^  (base_uint256)b; }
-inline const uint256 operator&(const uint256& a, const base_uint256& b) { return (base_uint256)a &  (base_uint256)b; }
-inline const uint256 operator|(const uint256& a, const base_uint256& b) { return (base_uint256)a |  (base_uint256)b; }
-inline const uint256 operator+(const uint256& a, const base_uint256& b) { return (base_uint256)a +  (base_uint256)b; }
-inline const uint256 operator-(const uint256& a, const base_uint256& b) { return (base_uint256)a -  (base_uint256)b; }
-
-inline bool operator<(const uint256& a, const uint256& b)               { return (base_uint256)a <  (base_uint256)b; }
-inline bool operator<=(const uint256& a, const uint256& b)              { return (base_uint256)a <= (base_uint256)b; }
-inline bool operator>(const uint256& a, const uint256& b)               { return (base_uint256)a >  (base_uint256)b; }
-inline bool operator>=(const uint256& a, const uint256& b)              { return (base_uint256)a >= (base_uint256)b; }
-inline bool operator==(const uint256& a, const uint256& b)              { return (base_uint256)a == (base_uint256)b; }
-inline bool operator!=(const uint256& a, const uint256& b)              { return (base_uint256)a != (base_uint256)b; }
-inline const uint256 operator^(const uint256& a, const uint256& b)      { return (base_uint256)a ^  (base_uint256)b; }
-inline const uint256 operator&(const uint256& a, const uint256& b)      { return (base_uint256)a &  (base_uint256)b; }
-inline const uint256 operator|(const uint256& a, const uint256& b)      { return (base_uint256)a |  (base_uint256)b; }
-inline const uint256 operator+(const uint256& a, const uint256& b)      { return (base_uint256)a +  (base_uint256)b; }
-inline const uint256 operator-(const uint256& a, const uint256& b)      { return (base_uint256)a -  (base_uint256)b; }
-
 #endif