[GitHub] [arrow] edponce commented on a diff in pull request #12660: ARROW-15965: [C++][Python] Add Scalar constructor of RoundToMultipleOptions to Python

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

edponce commented on code in PR #12660:
URL: https://github.com/apache/arrow/pull/12660#discussion_r850529787


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cpp/src/arrow/compute/kernels/scalar_arithmetic.cc:
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@@ -1453,20 +1447,20 @@ struct RoundToMultiple<ArrowType, kRoundMode, enable_if_decimal<ArrowType>> {
   bool has_halfway_point;
 
   explicit RoundToMultiple(const State& state, const DataType& out_ty)
-      : ty(checked_cast<const ArrowType&>(out_ty)) {
-    const auto& options = state.options;
-    DCHECK(options.multiple);
-    DCHECK(options.multiple->is_valid);
-    DCHECK(options.multiple->type->Equals(out_ty));
-    multiple = UnboxScalar<ArrowType>::Unbox(*options.multiple);
-    half_multiple = multiple;
-    half_multiple /= 2;
-    neg_half_multiple = -half_multiple;
-    has_halfway_point = multiple.low_bits() % 2 == 0;
-  }
+      : ty(checked_cast<const ArrowType&>(out_ty)),
+        multiple(UnboxScalar<ArrowType>::Unbox(*state.options.multiple)),
+        half_multiple(multiple / 2),
+        neg_half_multiple(-half_multiple),
+        has_halfway_point(multiple.low_bits() % 2 == 0) {}
 
   template <typename T = ArrowType, typename CType = typename TypeTraits<T>::CType>
   enable_if_decimal_value<CType> Call(KernelContext* ctx, CType arg, Status* st) const {
+    // Return zeros if `multiple` option is zero.

Review Comment:
   Good catch. The general form of rounding to a multiple is `round(value / multiple) * multiple` which is not defined for `multiple = 0` (div-by-zero). Nevertheless, `mround` in Excel returns 0 when `multiple = 0`.
   Now, I think we should not support a `multiple = 0` and treat it as an error.



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