[GitHub] [arrow-rs] tustvold opened a new issue, #3265: Decimal128 to Decimal256 Silently Overflows

[GitBox <gi...@apache.org>]

tustvold opened a new issue, #3265:
URL: https://github.com/apache/arrow-rs/issues/3265

   **Describe the bug**
   <!--
   A clear and concise description of what the bug is.
   -->
   
   ```
   #[test]
       fn test_cast_decimal128_to_decimal256_negative() {
           let input_type = DataType::Decimal128(10, 3);
           let output_type = DataType::Decimal256(10, 5);
           assert!(can_cast_types(&input_type, &output_type));
           let array = vec![Some(i128::MAX), Some(i128::MIN)];
           let input_decimal_array = create_decimal_array(array, 10, 3).unwrap();
           let array = Arc::new(input_decimal_array) as ArrayRef;
   
           let hundred = i256::from_i128(100);
           generate_cast_test_case!(
               &array,
               Decimal256Array,
               &output_type,
               vec![
                   Some(i256::from_i128(i128::MAX).mul_wrapping(hundred)),
                   Some(i256::from_i128(i128::MIN).mul_wrapping(hundred))
               ]
           );
       }
   ```
   
   Fails with
   
   
   ```
   thread 'cast::tests::test_cast_decimal128_to_decimal256_negative' panicked at 'assertion failed: `(left == right)`
     left: `0`,
    right: `17014118346046923173168730371588410572700`', arrow-cast/src/cast.rs:7251:9
   ```
   
   The issue is that it is not performing the scaling operation in the destination type
   
   ```
   let iter = array.iter().map(|v| {
       v.and_then(|v| v.mul_checked(mul).ok().map(i256::from_i128))
   });
   let casted_array = unsafe {
       PrimitiveArray::<Decimal256Type>::from_trusted_len_iter(iter)
   };
   casted_array
       .with_precision_and_scale(*output_precision, *output_scale)
       .map(|a| Arc::new(a) as ArrayRef)
   ```
   
   **To Reproduce**
   <!--
   Steps to reproduce the behavior:
   -->
   
   **Expected behavior**
   <!--
   A clear and concise description of what you expected to happen.
   -->
   
   **Additional context**
   <!--
   Add any other context about the problem here.
   -->


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[GitHub] [arrow-rs] tustvold closed issue #3265: Decimal128 to Decimal256 Overflows

[GitBox <gi...@apache.org>]

tustvold closed issue #3265: Decimal128 to Decimal256 Overflows
URL: https://github.com/apache/arrow-rs/issues/3265


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[GitHub] [arrow-rs] alamb commented on issue #3265: Decimal128 to Decimal256 Overflows

[GitBox <gi...@apache.org>]

alamb commented on issue #3265:
URL: https://github.com/apache/arrow-rs/issues/3265#issuecomment-1344634813

   `label_issue.py` automatically added labels {'arrow'} from #3264


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