lidavidm commented on a change in pull request #11045:
URL: https://github.com/apache/arrow/pull/11045#discussion_r700199554
##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_test.cc
##########
@@ -587,6 +589,36 @@ TEST(Cast, Decimal256ToInt) {
CheckCast(negative_scale, ArrayFromJSON(int64(), "[1234567890000,
-120000]"), options);
}
+TEST(Cast, IntegerToDecimal) {
+ for (auto decimal_type : {decimal128(21, 2), decimal256(21, 2)}) {
+ for (auto integer_type : kIntegerTypes) {
+ CheckCast(
+ ArrayFromJSON(integer_type, "[0, 7, null, 100, 99]"),
+ ArrayFromJSON(decimal_type, R"(["0.00", "7.00", null, "100.00",
"99.00"])"));
+ }
+ }
+
+ // extreme value
+ for (auto decimal_type : {decimal128(19, 0), decimal256(19, 0)}) {
+ CheckCast(ArrayFromJSON(int64(), "[-9223372036854775808,
9223372036854775807]"),
+ ArrayFromJSON(decimal_type,
+ R"(["-9223372036854775808",
"9223372036854775807"])"));
+ CheckCast(ArrayFromJSON(uint64(), "[0, 18446744073709551615]"),
+ ArrayFromJSON(decimal_type, R"(["0", "18446744073709551615"])"));
+ }
+
+ // insufficient output precision
+ {
+ CastOptions options;
+
+ options.to_type = decimal128(5, 3);
+ CheckCastFails(ArrayFromJSON(int8(), "[0]"), options);
+
+ options.to_type = decimal256(76, 67);
+ CheckCastFails(ArrayFromJSON(int32(), "[0]"), options);
+ }
Review comment:
Should we file a follow up issue to allow truncation via an unsafe cast
in these cases?
##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_numeric.cc
##########
@@ -391,6 +391,49 @@ struct CastFunctor<O, I,
}
};
+// ----------------------------------------------------------------------
+// Integer to decimal
+
+struct IntegerToDecimal {
+ template <typename OutValue, typename IntegerType>
+ OutValue Call(KernelContext*, IntegerType val, Status* st) const {
+ auto maybe_decimal = OutValue(val).Rescale(0, out_scale_);
+ if (ARROW_PREDICT_TRUE(maybe_decimal.ok())) {
+ return maybe_decimal.MoveValueUnsafe();
+ }
+ *st = maybe_decimal.status();
+ return OutValue{};
+ }
+
+ int32_t out_scale_;
+};
+
+template <typename O, typename I>
+struct CastFunctor<O, I,
+ enable_if_t<is_decimal_type<O>::value &&
is_integer_type<I>::value>> {
+ static Status Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+ const auto& out_type = checked_cast<const O&>(*out->type());
+ const auto out_scale = out_type.scale();
+ const auto out_precision = out_type.precision();
+
+ // verify precision and scale
+ if (out_scale < 0) {
+ return Status::Invalid("Scale must be non-negative");
+ }
+ // maximal number of decimal digits for int8/16/32/64
+ constexpr std::array<int, 4> decimal_digits{3, 5, 10, 19};
+ using ctype = typename I::c_type;
+ static_assert(sizeof(ctype) <= 8, "");
+ if (out_precision < decimal_digits[BitUtil::Log2(sizeof(ctype))] +
out_scale) {
+ return Status::Invalid("Invalid output precision and scale");
Review comment:
nit: in the error message, it might be good to clarify that 1) the
precision is not great enough for the requested type and 2) include the minimal
precision necessary.
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