cyb70289 commented on a change in pull request #10364:
URL: https://github.com/apache/arrow/pull/10364#discussion_r645469007
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File path: cpp/src/arrow/compute/kernels/scalar_arithmetic.cc
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@@ -516,6 +520,141 @@ std::shared_ptr<ScalarFunction>
MakeUnarySignedArithmeticFunctionNotNull(
return func;
}
+// Decimal arithmetics
+struct BinaryDecimal : public KernelState {
+ const std::shared_ptr<DecimalType> left_type, right_type;
+ std::shared_ptr<DataType> out_type;
+
+ explicit BinaryDecimal(const KernelInitArgs& args)
+ : left_type(checked_pointer_cast<DecimalType>(args.inputs[0].type)),
+ right_type(checked_pointer_cast<DecimalType>(args.inputs[1].type)) {
+ DCHECK_EQ(left_type->id(), right_type->id());
+ }
+
+ // create instance of derived class T
+ template <typename T>
+ static Result<std::unique_ptr<KernelState>> Make(const KernelInitArgs& args)
{
+ auto op = ::arrow::internal::make_unique<T>(args);
+ if (op->left_type->scale() < 0 || op->right_type->scale() < 0) {
+ return Status::Invalid("Decimals with negative scales not supported");
+ }
+ RETURN_NOT_OK(op->Init(op->left_type->precision(), op->left_type->scale(),
+ op->right_type->precision(),
op->right_type->scale()));
+ return std::move(op);
+ }
+
+ // return error and stop kernel execution if output precision is out of bound
+ Status Init(int32_t out_prec, int32_t out_scale) {
+ if (left_type->id() == Type::DECIMAL128) {
+ ARROW_ASSIGN_OR_RAISE(out_type, Decimal128Type::Make(out_prec,
out_scale));
+ } else {
+ ARROW_ASSIGN_OR_RAISE(out_type, Decimal256Type::Make(out_prec,
out_scale));
+ }
+ return Status::OK();
+ }
+
+ Result<std::shared_ptr<DataType>> ResolveOutput(const
std::vector<ValueDescr>&) const {
+ return out_type;
+ }
+};
+
+template <bool IsSubtract>
+struct AddOrSubtractDecimal : public BinaryDecimal {
+ using BinaryDecimal::BinaryDecimal;
+
+ int32_t left_scaleup, right_scaleup;
+
+ // called by kernel::init()
+ static Result<std::unique_ptr<KernelState>> Make(KernelContext*,
+ const KernelInitArgs& args)
{
+ return BinaryDecimal::Make<AddOrSubtractDecimal<IsSubtract>>(args);
+ }
+
+ // figure out output type and arg scaling, called by Make()
+ Status Init(int32_t p1, int32_t s1, int32_t p2, int32_t s2) {
+ const int32_t out_scale = std::max(s1, s2);
+ const int32_t out_prec = std::max(p1 - s1, p2 - s2) + 1 + out_scale;
+ left_scaleup = out_scale - s1;
+ right_scaleup = out_scale - s2;
+ return BinaryDecimal::Init(out_prec, out_scale);
+ }
+
+ // called by kerne::exec() for each value pair
+ // TODO(yibo): avoid repeat rescaling of scalar arg
+ template <typename T, typename Arg0, typename Arg1>
+ T Call(KernelContext*, Arg0 left, Arg1 right, Status*) const {
+ if (left_scaleup > 0) left = left.IncreaseScaleBy(left_scaleup);
+ if (right_scaleup > 0) right = right.IncreaseScaleBy(right_scaleup);
+ if (IsSubtract) right = -right;
+ return left + right;
+ }
+};
+
+using AddDecimal = AddOrSubtractDecimal</*IsSubtract=*/false>;
+using SubtractDecimal = AddOrSubtractDecimal</*IsSubtract=*/true>;
+
+struct MultiplyDecimal : public BinaryDecimal {
+ using BinaryDecimal::BinaryDecimal;
+
+ static Result<std::unique_ptr<KernelState>> Make(KernelContext*,
+ const KernelInitArgs& args)
{
+ return BinaryDecimal::Make<MultiplyDecimal>(args);
+ }
+
+ Status Init(int32_t p1, int32_t s1, int32_t p2, int32_t s2) {
+ return BinaryDecimal::Init(p1 + p2 + 1, s1 + s2);
+ }
+
+ template <typename T, typename Arg0, typename Arg1>
+ T Call(KernelContext*, Arg0 left, Arg1 right, Status*) const {
+ return left * right;
+ }
+};
+
+struct DivideDecimal : public BinaryDecimal {
+ using BinaryDecimal::BinaryDecimal;
+
+ int32_t left_scaleup;
+
+ static Result<std::unique_ptr<KernelState>> Make(KernelContext*,
+ const KernelInitArgs& args)
{
+ return BinaryDecimal::Make<DivideDecimal>(args);
+ }
+
+ Status Init(int32_t p1, int32_t s1, int32_t p2, int32_t s2) {
+ //
https://docs.aws.amazon.com/redshift/latest/dg/r_numeric_computations201.html
Review comment:
Added explanation to compute.rst
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