From c457904a6172d5924cb545af24e4ae692b735f66 Mon Sep 17 00:00:00 2001
From: Jacek Sieka <jacek@status.im>
Date: Tue, 3 Dec 2019 11:28:00 +0100
Subject: [PATCH] avoid recursion when getting lmd ancestors

---
 beacon_chain/fork_choice.nim | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/beacon_chain/fork_choice.nim b/beacon_chain/fork_choice.nim
index cc3b8bddc..018b61e4c 100644
--- a/beacon_chain/fork_choice.nim
+++ b/beacon_chain/fork_choice.nim
@@ -1,16 +1,28 @@
 import
   deques, options, sequtils, tables,
-  chronicles,
   ./spec/[datatypes, crypto, helpers],
   ./attestation_pool, ./beacon_node_types, ./ssz
 
 func get_ancestor(blck: BlockRef, slot: Slot): BlockRef =
-  if blck.slot == slot:
-    blck
-  elif blck.slot < slot:
-    nil
-  else:
-    get_ancestor(blck.parent, slot)
+  var blck = blck
+
+  var depth = 0
+  const maxDepth = (100'i64 * 365 * 24 * 60 * 60 div SECONDS_PER_SLOT.int)
+
+  while true:
+    if blck.slot == slot:
+      return blck
+
+    if blck.slot < slot:
+      return nil
+
+    if blck.parent == nil:
+      return nil
+
+    doAssert depth < maxDepth
+    depth += 1
+
+    blck = blck.parent
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.8.4/specs/core/0_fork-choice.md
 # The structure of this code differs from the spec since we use a different