feat(mpi): add MPI reduction op conversion logic

Signed-off-by: Gabriel Dos Santos <[email protected]>

Author: dssgabriel

src/KokkosComm/mpi/impl/reduction_op.hpp

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright Contributors to the Kokkos project
+
+#pragma once
+
+#include <type_traits>
+
+#include <mpi.h>
+
+#include <KokkosComm/concepts.hpp>
+#include <KokkosComm/reduction_op.hpp>
+
+namespace KokkosComm::mpi::Impl {
+
+template <ReductionOperator RedOp>
+constexpr auto reduction_op() -> MPI_Op {
+  if constexpr (std::is_same_v<RedOp, Max>) {
+    return MPI_MAX;
+  } else if constexpr (std::is_same_v<RedOp, Min>) {
+    return MPI_MIN;
+  } else if constexpr (std::is_same_v<RedOp, Sum>) {
+    return MPI_SUM;
+  } else if constexpr (std::is_same_v<RedOp, Prod>) {
+    return MPI_PROD;
+  } else if constexpr (std::is_same_v<RedOp, LAnd>) {
+    return MPI_LAND;
+  } else if constexpr (std::is_same_v<RedOp, BAnd>) {
+    return MPI_BAND;
+  } else if constexpr (std::is_same_v<RedOp, LOr>) {
+    return MPI_LOR;
+  } else if constexpr (std::is_same_v<RedOp, BOr>) {
+    return MPI_BOR;
+  } else if constexpr (std::is_same_v<RedOp, LXor>) {
+    return MPI_LXOR;
+  } else if constexpr (std::is_same_v<RedOp, BXor>) {
+    return MPI_BXOR;
+  } else if constexpr (std::is_same_v<RedOp, MaxLoc>) {
+    return MPI_MAXLOC;
+  } else if constexpr (std::is_same_v<RedOp, MinLoc>) {
+    return MPI_MINLOC;
+  } else {
+    static_assert(std::is_void_v<RedOp>, "mpi::Impl::reduction_op: operator not implemented");
+    return MPI_SUM;  // unreachable
+  }
+}
+
+template <ReductionOperator RedOp>
+inline constexpr MPI_Op reduction_op_v = reduction_op<RedOp>();
+
+}  // namespace KokkosComm::mpi::Impl