Support bitwise allreduce operations in the communicator (#8623)

rabit/include/rabit/internal/engine.h

@@ -133,7 +133,9 @@ enum OpType {
   kMax = 0,
   kMin = 1,
   kSum = 2,
-  kBitwiseOR = 3
+  kBitwiseAND = 3,
+  kBitwiseOR = 4,
+  kBitwiseXOR = 5,
 };
 /*!\brief enum of supported data types */
 enum DataType {

rabit/include/rabit/internal/rabit-inl.h

@@ -85,6 +85,13 @@ struct Sum {
     dst += src;
   }
 };
+struct BitAND {
+  static const engine::mpi::OpType kType = engine::mpi::kBitwiseAND;
+  template<typename DType>
+  inline static void Reduce(DType &dst, const DType &src) { // NOLINT(*)
+    dst &= src;
+  }
+};
 struct BitOR {
   static const engine::mpi::OpType kType = engine::mpi::kBitwiseOR;
   template<typename DType>
@@ -92,6 +99,13 @@ struct BitOR {
     dst |= src;
   }
 };
+struct BitXOR {
+  static const engine::mpi::OpType kType = engine::mpi::kBitwiseXOR;
+  template<typename DType>
+  inline static void Reduce(DType &dst, const DType &src) { // NOLINT(*)
+    dst ^= src;
+  }
+};
 template <typename OP, typename DType>
 inline void Reducer(const void *src_, void *dst_, int len, const MPI::Datatype &) {
   const DType *src = static_cast<const DType *>(src_);

rabit/include/rabit/rabit.h

@@ -50,11 +50,21 @@ struct Min;
  * \brief sum reduction operator
  */
 struct Sum;
+/*!
+ * \class rabit::op::BitAND
+ * \brief bitwise AND reduction operator
+ */
+struct BitAND;
 /*!
  * \class rabit::op::BitOR
  * \brief bitwise OR reduction operator
  */
 struct BitOR;
+/*!
+ * \class rabit::op::BitXOR
+ * \brief bitwise XOR reduction operator
+ */
+struct BitXOR;
 }  // namespace op
 /*!
  * \brief initializes rabit, call this once at the beginning of your program