Optimize JSON-RPC getblockhash

- If the height is in the first half, start at the genesis block and go up, rather than at the top
- Cache the last lookup and use it as a reference point if it's close to the next request, to make linear lookups always fast

1 files changed, 1 insertions, 4 deletions

diff --git a/src/bitcoinrpc.cpp b/src/bitcoinrpc.cpp
index 62b0b497ed..474207bdce 100644
--- a/src/bitcoinrpc.cpp
+++ b/src/bitcoinrpc.cpp
@@ -2023,10 +2023,7 @@ Value getblockhash(const Array& params, bool fHelp)
     if (nHeight < 0 || nHeight > nBestHeight)
         throw runtime_error("Block number out of range.");
 
-    CBlock block;
-    CBlockIndex* pblockindex = mapBlockIndex[hashBestChain];
-    while (pblockindex->nHeight > nHeight)
-        pblockindex = pblockindex->pprev;
+    CBlockIndex* pblockindex = FindBlockByHeight(nHeight);
     return pblockindex->phashBlock->GetHex();
 }