From 1cc0e96e9cc7aa094ddee9fe5b192b3ac1a59da8 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Thu, 26 Mar 2015 11:06:27 -0700
Subject: [PATCH] Trivial optimization: use GetAncestor to compute new target

---
 src/pow.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/pow.cpp b/src/pow.cpp
index 3c5a8d9d9..cf7ac387f 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -42,9 +42,9 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
     }
 
     // Go back by what we want to be 14 days worth of blocks
-    const CBlockIndex* pindexFirst = pindexLast;
-    for (int i = 0; pindexFirst && i < params.DifficultyAdjustmentInterval()-1; i++)
-        pindexFirst = pindexFirst->pprev;
+    int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1);
+    assert(nHeightFirst >= 0);
+    const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
     assert(pindexFirst);
 
     return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);