From 3e3bd07ff8aa4346814c2cea6eb3f1a65669e3f6 Mon Sep 17 00:00:00 2001
From: ChJR <chjr8815@gmail.com>
Date: Fri, 20 Nov 2020 02:46:53 +0900
Subject: [PATCH] Fix overflow of string reverse iteration

This issue does not appear in CI.
---
 vm/src/builtins/pystr.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/vm/src/builtins/pystr.rs b/vm/src/builtins/pystr.rs
index 45ebe0100..f19a90666 100644
--- a/vm/src/builtins/pystr.rs
+++ b/vm/src/builtins/pystr.rs
@@ -180,7 +180,11 @@ impl PyIter for PyStrReverseIterator {
                     break;
                 }
             }
-            start.unwrap_or(end - 4)
+            if end < 4 {
+                start.unwrap_or(0)
+            } else {
+                start.unwrap_or(end - 4)
+            }
         };
 
         let stored = zelf.position.swap(start);