xuanyuanking commented on a change in pull request #28937:
URL: https://github.com/apache/spark/pull/28937#discussion_r446613486
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File path:
common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
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@@ -341,8 +341,17 @@ public UTF8String substringSQL(int pos, int length) {
// to the -ith element before the end of the sequence. If a start index i
is 0, it
// refers to the first element.
int len = numChars();
+ // `len + pos` does not overflow as `len >= 0`.
Review comment:
The negative `pos` here `refers to the -ith element before the end of
the sequence`, so if pos = Integer.MIN_VALUE, then the start should be `pos +
len`. The final result of `EMPTY_UTF8` will be returned by `substring` when its
param start and until are both negative. I also added a UT in 4dcfe81.
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