IBD check uses minimumchain work instead of checkpoints.

This introduces a 'minimum chain work' chainparam which is intended
 to be the known amount of work in the chain for the network at the
 time of software release.  If you don't have this much work, you're
 not yet caught up.

This is used instead of the count of blocks test from checkpoints.

This criteria is trivial to keep updated as there is no element of
subjectivity, trust, or position dependence to it. It is also a more
reliable metric of sync status than a block count.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 5e17ec6251..6b33539a2e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1740,7 +1740,9 @@ bool IsInitialBlockDownload()
         return false;
     if (fImporting || fReindex)
         return true;
-    if (fCheckpointsEnabled && chainActive.Height() < Checkpoints::GetTotalBlocksEstimate(chainParams.Checkpoints()))
+    if (chainActive.Tip() == NULL)
+        return true;
+    if (chainActive.Tip()->nChainWork < UintToArith256(chainParams.GetConsensus().nMinimumChainWork))
         return true;
     bool state = (chainActive.Height() < pindexBestHeader->nHeight - 24 * 6 ||
             std::max(chainActive.Tip()->GetBlockTime(), pindexBestHeader->GetBlockTime()) < GetTime() - nMaxTipAge);
@@ -1774,7 +1776,7 @@ void CheckForkWarningConditions()
 {
     AssertLockHeld(cs_main);
     // Before we get past initial download, we cannot reliably alert about forks
-    // (we assume we don't get stuck on a fork before the last checkpoint)
+    // (we assume we don't get stuck on a fork before finishing our initial sync)
     if (IsInitialBlockDownload())
         return;