do length check in PartialString::range_from (#412)

2020-04-28 17:20:14 -06:00
parent 97115a9c1c
commit eefd36b50d
1 changed files with 5 additions and 1 deletions
--- 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]