gruuya commented on PR #8700:
URL: https://github.com/apache/arrow-rs/pull/8700#issuecomment-3696873750
> The current implementation has an overflow issue. You can test with the
following code:
>
> ```
> let result =
parse_decimal::<Decimal128Type>("20000000000000000000000000000000000002", 38,
0).unwrap();
> assert_eq!(result, 20000000000000000000000000000000000002i128);
> let result =
parse_decimal::<Decimal128Type>("20000000000000000000000000000000000002.0", 38,
0).unwrap();
> assert_eq!(result, 20000000000000000000000000000000000002i128);
> ```
>
> The first assert will pass. The second assert will fail:
>
> ```
> assertion `left == right` failed
> left: -14028236692093846346337460743176821143
> right: 20000000000000000000000000000000000002
> ```
>
> There is apparently an interger overflow.
Great catch, thanks!
I revised the implementation a bit, and tried a drive-by `parse_e_notation`
simplification. We won't hit the integer overflow in this case anymore (added a
test for it too), since we now avoid the redundant `result =
result.mul_wrapping(base)` unless we hit an e-notation (in which case we need
to do it since we don;t know ahead of time what are the actual non-fractional
digits then).
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