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fix sum decimal array overflow behavior with scalars #6431

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Merged
joseph-isaacs merged 2 commits into from
Feb 11, 2026
Merged

fix sum decimal array overflow behavior with scalars #6431

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8fb1dc9
fix sum decimal array overflow
connortsui20 Feb 11, 2026
838d354
dont match validity twice
connortsui20 Feb 11, 2026
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127 changes: 76 additions & 51 deletions vortex-array/src/arrays/decimal/compute/sum.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@ use num_traits::AsPrimitive;
use num_traits::CheckedAdd;
use vortex_buffer::BitBuffer;
use vortex_buffer::Buffer;
use vortex_dtype::DType;
use vortex_dtype::DecimalDType;
use vortex_dtype::DecimalType;
use vortex_dtype::Nullability::Nullable;
use vortex_dtype::match_each_decimal_value_type;
Expand All @@ -24,75 +26,77 @@ use crate::expr::stats::Stat;
use crate::register_kernel;

impl SumKernel for DecimalVTable {
#[expect(
clippy::cognitive_complexity,
reason = "complexity from nested match_each_* macros"
)]
fn sum(&self, array: &DecimalArray, accumulator: &Scalar) -> VortexResult<Scalar> {
let return_dtype = Stat::Sum
.dtype(array.dtype())
.vortex_expect("sum for decimals exists");
let return_decimal_dtype = return_dtype
let return_decimal_dtype = *return_dtype
.as_decimal_opt()
.vortex_expect("must be decimal");

// Extract the initial value as a DecimalValue
// Extract the initial value as a `DecimalValue`.
let initial_decimal = accumulator
.as_decimal()
.decimal_value()
.vortex_expect("cannot be null");

match array.validity_mask()? {
let mask = array.validity_mask()?;
let validity = match &mask {
Mask::AllTrue(_) => None,
Mask::Values(mask_values) => Some(mask_values.bit_buffer()),
Mask::AllFalse(_) => {
vortex_bail!("invalid state, all-null array should be checked by top-level sum fn")
}
Mask::AllTrue(_) => {
let values_type = DecimalType::smallest_decimal_value_type(return_decimal_dtype);
match_each_decimal_value_type!(array.values_type(), |I| {
match_each_decimal_value_type!(values_type, |O| {
let initial_val: O = initial_decimal
.cast()
.vortex_expect("cannot fail to cast initial value");
if let Some(sum) = sum_decimal(array.buffer::<I>(), initial_val) {
Ok(Scalar::decimal(
DecimalValue::from(sum),
*return_decimal_dtype,
Nullable,
))
} else {
Ok(Scalar::null(return_dtype))
}
})
})
}
Mask::Values(mask_values) => {
let values_type = DecimalType::smallest_decimal_value_type(return_decimal_dtype);
match_each_decimal_value_type!(array.values_type(), |I| {
match_each_decimal_value_type!(values_type, |O| {
let initial_val: O = initial_decimal
.cast()
.vortex_expect("cannot fail to cast initial value");

if let Some(sum) = sum_decimal_with_validity(
array.buffer::<I>(),
mask_values.bit_buffer(),
initial_val,
) {
Ok(Scalar::decimal(
DecimalValue::from(sum),
*return_decimal_dtype,
Nullable,
))
} else {
Ok(Scalar::null(return_dtype))
}
})
})
}
}
};

let values_type = DecimalType::smallest_decimal_value_type(&return_decimal_dtype);
match_each_decimal_value_type!(array.values_type(), |I| {
match_each_decimal_value_type!(values_type, |O| {
let initial_val: O = initial_decimal
.cast()
.vortex_expect("cannot fail to cast initial value");

Ok(sum_to_scalar(
array.buffer::<I>(),
validity,
initial_val,
return_decimal_dtype,
&return_dtype,
))
})
})
}
}

/// Compute the checked sum and convert the result to a [`Scalar`].
///
/// Returns a null scalar if the sum overflows the underlying integer type or if the result
/// exceeds the declared decimal precision.
fn sum_to_scalar<T, O>(
values: Buffer<T>,
validity: Option<&BitBuffer>,
initial: O,
return_decimal_dtype: DecimalDType,
return_dtype: &DType,
) -> Scalar
where
T: AsPrimitive<O>,
O: Copy + CheckedAdd + Into<DecimalValue> + 'static,
{
let raw_sum = match validity {
Some(v) => sum_decimal_with_validity(values, v, initial),
None => sum_decimal(values, initial),
};

raw_sum
.map(Into::<DecimalValue>::into)
// We have to make sure that the decimal value fits the precision of the decimal dtype.
.filter(|v| v.fits_in_precision(return_decimal_dtype))
.map(|v| Scalar::decimal(v, return_decimal_dtype, Nullable))
// If an overflow occurs during summation, or final value does not fit, then return a null.
.unwrap_or_else(|| Scalar::null(return_dtype.clone()))
}

fn sum_decimal<T: AsPrimitive<I>, I: Copy + CheckedAdd + 'static>(
values: Buffer<T>,
initial: I,
Expand Down Expand Up @@ -371,6 +375,27 @@ mod tests {
assert_eq!(result, expected);
}

#[test]
fn test_sum_precision_overflow_without_i256_overflow() {
// Construct values that individually fit in precision 76 but whose sum exceeds it,
// while still fitting in `i256`. This ensures we return null for precision overflow
// and not just for arithmetic overflow.
let ten_to_38 = i256::from_i128(10i128.pow(38));
let ten_to_75 = ten_to_38 * i256::from_i128(10i128.pow(37));
// 6 * 10^75 is a 76-digit number, which fits in precision 76.
let val = ten_to_75 * i256::from_i128(6);

let decimal_dtype = DecimalDType::new(76, 0);
let decimal = DecimalArray::new(buffer![val, val], decimal_dtype, Validity::AllValid);

// Sum = 12 * 10^75 = 1.2 * 10^76, which exceeds precision 76 but fits in `i256`.
let result = sum(decimal.as_ref()).unwrap();
assert_eq!(
result,
Scalar::null(DType::Decimal(decimal_dtype, Nullability::Nullable))
);
}

#[test]
fn test_i256_overflow() {
let decimal_dtype = DecimalDType::new(76, 0);
Expand Down
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