From 807bd662b2d70e578185ad284b39ae16c73a6dcc Mon Sep 17 00:00:00 2001
From: Ethan Buchman <ethan@coinculture.info>
Date: Sat, 8 Aug 2015 22:20:19 -0400
Subject: [PATCH] vm: catch stack underflow on Peek()

---
 vm/stack.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/vm/stack.go b/vm/stack.go
index 9dfff4df6..7dae3e71d 100644
--- a/vm/stack.go
+++ b/vm/stack.go
@@ -104,6 +104,10 @@ func (st *Stack) Dup(n int) {
 
 // Not an opcode, costs no gas.
 func (st *Stack) Peek() Word256 {
+	if st.ptr == 0 {
+		st.setErr(ErrDataStackUnderflow)
+		return Zero256
+	}
 	return st.data[st.ptr-1]
 }