jkosh44 commented on code in PR #14489:
URL: https://github.com/apache/datafusion/pull/14489#discussion_r1941739956
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datafusion/functions-nested/src/extract.rs:
##########
@@ -487,7 +487,17 @@ where
// 0 ~ len - 1
let adjusted_zero_index = if index < 0 {
if let Ok(index) = index.try_into() {
- index + len
+ // When index < 0 and -index > length, index is clamped to the
beginning of the list.
+ // Otherwise, when index < 0, the index is counted from the
end of the list.
+ //
+ // Note, we actually test the contrapositive, index < -length,
because negating a
+ // negative will panic if the negative is equal to the
smallest representable value
+ // while negating a positive is always safe.
+ if index < (O::zero() - O::one()) * len {
Review Comment:
If anyone knows a simpler way of negating `len`, please let me know.
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