From eefd36b50d5bcc1b43818d9ce49de101afb40dcd Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Tue, 28 Apr 2020 17:20:14 -0600
Subject: [PATCH] do length check in PartialString::range_from (#412)

---
 src/prolog/machine/partial_string.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/prolog/machine/partial_string.rs b/src/prolog/machine/partial_string.rs
index ea36d409..2d821ac4 100644
--- a/src/prolog/machine/partial_string.rs
+++ b/src/prolog/machine/partial_string.rs
@@ -202,7 +202,11 @@ impl PartialString {
 
     #[inline]
     pub fn range_from(&self, index: RangeFrom<usize>) -> PStrIter {
-        PStrIter::from(self.buf, self.len - '\u{0}'.len_utf8(), index.start)
+        if self.len >= '\u{0}'.len_utf8() {
+            PStrIter::from(self.buf, self.len - '\u{0}'.len_utf8(), index.start)
+        } else {
+            PStrIter::from(self.buf, 0, 0)
+        }
     }
 
     #[inline]
-- 
2.54.0