[GitHub] [arrow] lidavidm commented on a change in pull request #10349: ARROW-12744: [C++][Compute] Add rounding kernel

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

lidavidm commented on a change in pull request #10349:
URL: https://github.com/apache/arrow/pull/10349#discussion_r658733299



##########
File path: cpp/src/arrow/compute/kernels/scalar_arithmetic.cc
##########
@@ -454,6 +456,159 @@ struct PowerChecked {
   }
 };
 
+using RoundState = internal::OptionsWrapper<RoundOptions>;
+
+struct Round {
+  template <typename T, enable_if_t<std::is_floating_point<T>::value, bool> = true>
+  static constexpr bool ApproxEqual(T x, T y, int ulp = 8) {
+    // https://en.cppreference.com/w/cpp/types/numeric_limits/epsilon
+    // The machine epsilon has to be scaled to the magnitude of the values used
+    // and multiplied by the desired precision in ULPs (units in the last place)
+    return (std::fabs(x - y) <=
+            (std::numeric_limits<T>::epsilon() * std::fabs(x + y) * ulp))
+           // unless the result is subnormal
+           || (std::fabs(x - y) < std::numeric_limits<T>::min());
+  }
+
+  template <typename T, enable_if_t<std::is_floating_point<T>::value, bool> = true>
+  static constexpr bool IsHalf(T val) {
+    // |frac| == 0.5?
+    return ApproxEqual(std::fabs(std::fmod(val, T(1))), T(0.5));
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> RoundWithMultiple(T val, T mult) {
+    return (val / mult) * mult;
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> Floor(T val) {
+    return std::floor(val);
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> Ceiling(T val) {
+    return std::ceil(val);
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> Truncate(T val) {
+    return std::trunc(val);
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> TowardsInfinity(T val) {
+    return std::signbit(val) ? std::floor(val) : std::ceil(val);
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> HalfDown(T val) {
+    return std::ceil(val - T(0.5));
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> HalfUp(T val) {
+    return std::floor(val + T(0.5));
+  }
+
+  template <typename T>
+  static enable_if_floating_point<T> HalfToEven(T val) {
+    if (IsHalf(val)) {
+      auto floor = std::floor(val);
+      // Odd + 1, Even + 0
+      return floor + (std::fmod(std::fabs(floor), T(2)) >= T(1));
+    }
+    return std::round(val);
+  }
+
+  template <typename T>
+  static enable_if_floating_point<T> HalfToOdd(T val) {
+    if (IsHalf(val)) {
+      auto floor = std::floor(val);
+      // Odd + 0, Even + 1
+      return floor + (std::fmod(std::fabs(floor), T(2)) < T(1));
+    }
+    return std::round(val);
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> Nearest(T val) {
+    return std::round(val);
+  }
+
+  template <typename T>
+  static constexpr enable_if_floating_point<T> HalfTowardsZero(T val) {
+    return std::copysign(std::ceil(std::fabs(val) - T(0.5)), val);
+  }
+
+  template <typename T, typename Arg,
+            enable_if_t<std::is_integral<Arg>::value, bool> = true>
+  static constexpr enable_if_floating_point<T> Call(KernelContext* ctx, Arg arg,
+                                                    Status* st) {
+    return Call<T, T>(ctx, T(arg), st);
+  }
+
+  template <typename T, typename Arg,
+            enable_if_t<std::is_floating_point<Arg>::value, bool> = true>
+  static enable_if_floating_point<T> Call(KernelContext* ctx, Arg arg, Status* st) {
+    const RoundOptions& options = RoundState::Get(ctx);

Review comment:
       The default options instance needs to be declared static, e.g. see JoinOptions: https://github.com/apache/arrow/blob/c4a20e98a3294b32e51c879e927878e9fb6e799b/cpp/src/arrow/compute/kernels/scalar_string.cc#L3566
   
   Currently, the default options are allocated on the stack in RegisterScalarArithmetic and will go away when the function returns. Then when you call the function, it references the already-deallocated options and crashes.




-- 
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org