From 0df67f1f7ab4adfe9f0b3ba6276e737b37826464 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Tue, 31 Mar 2015 19:15:42 -0700
Subject: [PATCH] Simplify hash loop code

---
 src/miner.cpp | 30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

diff --git a/src/miner.cpp b/src/miner.cpp
index cf08b7822..44661fd13 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -365,33 +365,23 @@ void IncrementExtraNonce(CBlock* pblock, CBlockIndex* pindexPrev, unsigned int&
 
 //
 // ScanHash scans nonces looking for a hash with at least some zero bits.
-// The nonce is usually preserved between calls, but periodically or if the
-// nonce is 0xffff0000 or above, the block is rebuilt and nNonce starts over at
-// zero.
+// The nonce is usually preserved between calls, but periodically the block is
+// rebuilt and nNonce starts over at zero.
 //
-bool static ScanHash(const CBlockHeader *pblock, uint32_t& nNonce, uint256 *phash)
+bool static ScanHash(CBlockHeader *pblock, uint256 *phash)
 {
-    // Write the first 76 bytes of the block header to a double-SHA256 state.
-    CHash256 hasher;
-    CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
-    ss << *pblock;
-    assert(ss.size() == 80);
-    hasher.Write((unsigned char*)&ss[0], 76);
-
     while (true) {
-        nNonce++;
+        pblock->nNonce++;
 
-        // Write the last 4 bytes of the block header (the nonce) to a copy of
-        // the double-SHA256 state, and compute the result.
-        CHash256(hasher).Write((unsigned char*)&nNonce, 4).Finalize((unsigned char*)phash);
+        *phash = (CHashWriter(SER_GETHASH, 0) << *pblock).GetHash();
 
         // Return the nonce if the hash has at least some zero bits,
         // caller will check if it has enough to reach the target
         if (((uint16_t*)phash)[15] == 0)
             return true;
 
-        // If nothing found after trying for a while, return -1
-        if ((nNonce & 0xfff) == 0)
+        // If nothing found after trying for a while, return false.
+        if ((pblock->nNonce & 0xfff) == 0)
             return false;
     }
 }
@@ -478,15 +468,13 @@ void static BitcoinMiner(CWallet *pwallet)
             int64_t nStart = GetTime();
             arith_uint256 hashTarget = arith_uint256().SetCompact(pblock->nBits);
             uint256 hash;
-            uint32_t nNonce = 0;
             while (true) {
                 // Check if something found
-                if (ScanHash(pblock, nNonce, &hash))
+                if (ScanHash(pblock, &hash))
                 {
                     if (UintToArith256(hash) <= hashTarget)
                     {
                         // Found a solution
-                        pblock->nNonce = nNonce;
                         assert(hash == pblock->GetHash());
 
                         SetThreadPriority(THREAD_PRIORITY_NORMAL);
@@ -508,7 +496,7 @@ void static BitcoinMiner(CWallet *pwallet)
                 // Regtest mode doesn't require peers
                 if (vNodes.empty() && Params().MiningRequiresPeers())
                     break;
-                if (nNonce >= 0xffff0000)
+                if (pblock->nNonce >= 0xffff0000)
                     break;
                 if (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLast && GetTime() - nStart > 60)
                     break;