edponce commented on a change in pull request #10349:
URL: https://github.com/apache/arrow/pull/10349#discussion_r704005402
##########
File path: cpp/src/arrow/compute/kernels/scalar_arithmetic.cc
##########
@@ -852,24 +854,232 @@ struct LogbChecked {
}
};
+struct RoundUtil {
+ template <typename T>
+ static constexpr enable_if_t<std::is_floating_point<T>::value, bool>
IsApproxEqual(
+ const T a, const T b, const T abs_tol = kDefaultAbsoluteTolerance) {
+ return std::fabs(a - b) <= abs_tol;
+ }
+
+ template <typename T>
+ static constexpr enable_if_t<std::is_floating_point<T>::value, bool>
IsApproxInt(
+ const T val, const T abs_tol = kDefaultAbsoluteTolerance) {
+ // |frac| ~ 0.0?
+ return IsApproxEqual(val, std::round(val), abs_tol);
+ }
+
+ template <typename T>
+ static constexpr enable_if_t<std::is_floating_point<T>::value, bool>
IsApproxHalfInt(
+ const T val, const T abs_tol = kDefaultAbsoluteTolerance) {
+ // |frac| ~ 0.5?
+ return IsApproxEqual(val - std::floor(val), T(0.5), abs_tol);
+ }
+
+ template <typename T>
+ static enable_if_floating_point<T> Pow10(const int64_t power) {
+ const T lut[]{1e0F, 1e1F, 1e2F, 1e3F, 1e4F, 1e5F, 1e6F, 1e7F,
+ 1e8F, 1e9F, 1e10F, 1e11F, 1e12F, 1e13F, 1e14F, 1e15F,
+ 1e16F, 1e17F, 1e18F, 1e19F, 1e20F, 1e21F, 1e22F};
+ // Return NaN if index is out-of-range.
+ auto lut_size = (int64_t)(sizeof(lut) / sizeof(*lut));
+ return (power >= 0 && power < lut_size) ? lut[power] : std::nanf("");
+ }
+};
+
+// Specializations of rounding implementations for round kernels
+template <typename T, RoundMode>
+struct RoundImpl {};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::DOWN> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return std::floor(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::UP> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return std::ceil(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::TOWARDS_ZERO> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return std::signbit(val) ? std::ceil(val) : std::floor(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::TOWARDS_INFINITY> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return std::signbit(val) ? std::floor(val) : std::ceil(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::HALF_DOWN> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return RoundImpl<T, RoundMode::DOWN>::Round(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::HALF_UP> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return RoundImpl<T, RoundMode::UP>::Round(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::HALF_TOWARDS_ZERO> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return RoundImpl<T, RoundMode::TOWARDS_ZERO>::Round(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::HALF_TOWARDS_INFINITY> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return RoundImpl<T, RoundMode::TOWARDS_INFINITY>::Round(val);
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::HALF_TO_EVEN> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return std::round(val * T(0.5)) * 2;
+ }
+};
+
+template <typename T>
+struct RoundImpl<T, RoundMode::HALF_TO_ODD> {
+ static constexpr enable_if_floating_point<T> Round(const T val) {
+ return std::floor(val * T(0.5)) + std::ceil(val * T(0.5));
+ }
+};
+
+template <RoundMode RndMode>
+struct Round {
+ using RoundState = OptionsWrapper<RoundOptions>;
+
+ template <typename T, typename Arg>
+ static enable_if_floating_point<Arg, T> Call(KernelContext* ctx, Arg arg,
Status* st) {
+ static_assert(std::is_same<T, Arg>::value, "");
+ static_assert(RoundMode::HALF_DOWN > RoundMode::DOWN &&
+ RoundMode::HALF_DOWN > RoundMode::UP &&
+ RoundMode::HALF_DOWN > RoundMode::TOWARDS_ZERO &&
+ RoundMode::HALF_DOWN > RoundMode::TOWARDS_INFINITY &&
+ RoundMode::HALF_DOWN < RoundMode::HALF_UP &&
+ RoundMode::HALF_DOWN < RoundMode::HALF_TOWARDS_ZERO &&
+ RoundMode::HALF_DOWN < RoundMode::HALF_TOWARDS_INFINITY
&&
+ RoundMode::HALF_DOWN < RoundMode::HALF_TO_EVEN &&
+ RoundMode::HALF_DOWN < RoundMode::HALF_TO_ODD,
+ "Round modes prefixed with HALF need to be defined last in
enum and "
+ "the first HALF entry has to be HALF_DOWN.");
+
+ auto options = RoundState::Get(ctx);
+ auto pow10 = RoundUtil::Pow10<T>(std::llabs(options.ndigits));
+ if (std::isnan(pow10)) {
+ *st = Status::Invalid("out-of-range value for rounding digits");
+ return arg;
Review comment:
I agree, and I tried to make use of
[`KernelStateFromFunctionOptions`](https://github.com/apache/arrow/blob/master/cpp/src/arrow/compute/kernels/codegen_internal.h#L96)
but failed to make it work. The issues I encountered were:
* I do not know how to invoke `Init` from this wrapper (while allowing the
existing `Init` to be invoked first). Actually, I calculated `pow10` in the
constructor.
* An invalid `status` cannot be handled in constructor, it has to be `Init`.
* `Call` is a static function and member variable `state` is not.
Here is more or less what I tried:
```c++
struct RoundState {
RoundOptions options_;
Status status_ = Status::OK();
double pow10_;
explicit RoundState(KernelContext* ctx, RoundOptions options) :
options_(std::move(options)) {
pow10_ = RoundUtil::Pow10<double>(std::llabs(options_.ndigits));
if (std::isnan(pow10_)) {
// NOTE: There is no way to signal this invalid status outside of Call
(e.g., a PreExec method like in StringTransforms).
status_ = Status::Invalid("out-of-range value for rounding digits");
}
}
};
template <RoundMode RndMode>
struct Round {
using State = KernelStateFromFunctionOptions<RoundState, RoundOptions>;
const State& state_;
template <typename T, typename Arg>
static enable_if_floating_point<Arg, T> Call(KernelContext* ctx, Arg arg,
Status* st) {
static_assert(std::is_same<T, Arg>::value, "");
// NOTE: There is no way to signal this invalid status outside of Call
(e.g., a PreExec method).
if (state_.status_ != Status::OK()) {
*st = state_.status_;
return arg;
} else if (!std::isfinite(arg)) {
return arg;
}
auto pow10 = T(state_.pow10_);
...
}
};
```
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