IBD: do not check PoW (Yespower) during downloading headers (#122)

* IBD: do not check PoW (Yespower) during downloading headers
However this means checking PoW during IBD is, not actually skipped, but still checking in another places. This makes IBD much faster.
* remove: debug printf
* adding comment by volbil

src/validation.cpp

@@ -3047,6 +3047,13 @@ static bool CheckBlockHeader(const CBlockHeader& block, CValidationState& state,
     if (fCheckPOW && !CheckProofOfWork(block.GetPoWHash_cached(), block.nBits, consensusParams))
         return state.DoS(50, false, REJECT_INVALID, "high-hash", false, "proof of work failed");
 
+    // FIXME.SUGAR // check PoW: SKIPPED during downloading headers (IBD)
+    // You can see this log when IBD.
+    // This means PoW check during IBD is not actually skipped, but still its checking in another places.
+    // What we skipped is only when Downloading headers, but not else. This makes IBD much faster.
+    // if (IsInitialBlockDownload())
+    //     printf("%s IBD=%d CBH=%s\n", DateTimeStrFormat("%Y-%m-%d %H:%M:%S", GetTime()).c_str(), IsInitialBlockDownload(), block.GetHash().ToString().c_str());
+
     return true;
 }
 
@@ -3057,8 +3064,9 @@ bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::P
     if (block.fChecked)
         return true;
 
+    // FIXME.SUGAR // check PoW: SKIPPED during downloading headers (IBD)
     // Check that the header is valid (particularly PoW).  This is mostly
-    // redundant with the call in AcceptBlockHeader.
+    // redundant with the call in AcceptBlockHeader, but when IBD mode, its SKIPPED.
     if (!CheckBlockHeader(block, state, consensusParams, fCheckPOW))
         return false;
 
@@ -3334,7 +3342,9 @@ bool CChainState::AcceptBlockHeader(const CBlockHeader& block, CValidationState&
             return true;
         }
 
-        if (!CheckBlockHeader(block, state, chainparams.GetConsensus()))
+        // FIXME.SUGAR // check PoW: SKIPPED during downloading headers (IBD)
+        // IBD: do not check PoW (Yespower) during Download headers for performance reason
+        if (!IsInitialBlockDownload() && !CheckBlockHeader(block, state, chainparams.GetConsensus()))
             return error("%s: Consensus::CheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
 
         // Get prev block index