idx_abs_max: add customization point kokkos#96

Note the different behavior with kokkos-kernels,
tracked in issue kokkos#114.

examples/kokkos-based/CMakeLists.txt

@@ -2,5 +2,6 @@
 linalg_add_example(add_kokkos)
 linalg_add_example(dot_kokkos)
 linalg_add_example(dotc_kokkos)
+linalg_add_example(idx_abs_max_kokkos)
 linalg_add_example(simple_scale_kokkos)
 linalg_add_example(matrix_vector_product_kokkos)

examples/kokkos-based/idx_abs_max_kokkos.cpp

@@ -0,0 +1,42 @@
+#include <experimental/linalg>
+#include <iostream>
+
+int main(int argc, char* argv[])
+{
+  std::cout << "idx_abs_max example: calling kokkos-kernels" << std::endl;
+
+  std::size_t N = 10;
+  Kokkos::initialize(argc,argv);
+  {
+    using value_type = double;
+
+    Kokkos::View<value_type*> a_view("A",N);
+    value_type* a_ptr = a_view.data();
+
+    // Requires CTAD working, GCC 11.1 works but some others are buggy
+    // std::experimental::mdspan a(a_ptr,N);
+    using extents_type = std::experimental::extents<std::experimental::dynamic_extent>;
+    std::experimental::mdspan<value_type, extents_type> a(a_ptr,N);
+    a(0) =  0.5;
+    a(1) =  0.2;
+    a(2) =  0.1;
+    a(3) =  0.4;
+    a(4) = -0.8;
+    a(5) = -1.7;
+    a(6) = -0.3;
+    a(7) =  0.5;
+    a(8) = -1.7;
+    a(9) = -0.9;
+
+    namespace stdla = std::experimental::linalg;
+
+    // This goes to the base implementation
+    const auto idx = stdla::idx_abs_max(std::execution::seq, a);
+    printf("Seq result    = %i\n", idx);
+
+    // This forwards to KokkosKernels (https://github.com/kokkos/kokkos-kernels
+    const auto idx_kk = stdla::idx_abs_max(KokkosKernelsSTD::kokkos_exec<>(), a);
+    printf("Kokkos result = %i\n", idx_kk);
+  }
+  Kokkos::finalize();
+}

include/experimental/__p1673_bits/blas1_vector_idx_abs_max.hpp

@@ -48,11 +48,33 @@ namespace experimental {
 inline namespace __p1673_version_0 {
 namespace linalg {
 
+// begin anonymous namespace
+namespace {
+
+template <class Exec, class v_t, class = void>
+struct is_custom_idx_abs_max_avail : std::false_type {};
+
+template <class Exec, class v_t>
+struct is_custom_idx_abs_max_avail<
+  Exec, v_t,
+  std::enable_if_t<
+    std::is_integral<
+      decltype(idx_abs_max(std::declval<Exec>(),
+			   std::declval<v_t>()
+			   )
+	       )
+      >::value
+    >
+  >
+{
+  static constexpr bool value = !std::is_same<Exec,std::experimental::linalg::impl::inline_exec_t>::value;
+};
+
 template<class ElementType,
          extents<>::size_type ext0,
          class Layout,
          class Accessor>
-extents<>::size_type idx_abs_max(
+extents<>::size_type idx_abs_max_default_impl(
   std::experimental::mdspan<ElementType, std::experimental::extents<ext0>, Layout, Accessor> v)
 {
   using std::abs;
@@ -73,16 +95,38 @@ extents<>::size_type idx_abs_max(
   return maxInd; // FIXME check for NaN "never less than" stuff
 }
 
+} // end anonymous namespace
+
 template<class ExecutionPolicy,
          class ElementType,
          extents<>::size_type ext0,
          class Layout,
          class Accessor>
 extents<>::size_type idx_abs_max(
-  ExecutionPolicy&& /* exec */,
+  ExecutionPolicy&& exec,
+  std::experimental::mdspan<ElementType, std::experimental::extents<ext0>, Layout, Accessor> v)
+{
+  constexpr bool use_custom = is_custom_idx_abs_max_avail<
+    decltype(execpolicy_mapper(exec)), decltype(v)
+    >::value;
+
+  if constexpr(use_custom){
+    using return_type = extents<>::size_type;
+    return return_type(idx_abs_max(execpolicy_mapper(exec), v));
+  }
+  else{
+    return idx_abs_max_default_impl(v);
+  }
+}
+
+template<class ElementType,
+         extents<>::size_type ext0,
+         class Layout,
+         class Accessor>
+extents<>::size_type idx_abs_max(
   std::experimental::mdspan<ElementType, std::experimental::extents<ext0>, Layout, Accessor> v)
 {
-  return idx_abs_max(v);
+  return idx_abs_max(std::experimental::linalg::impl::default_exec_t(), v);
 }
 
 } // end namespace linalg

include/experimental/__p1673_bits/linalg_execpolicy_mapper.hpp

@@ -17,7 +17,7 @@ struct default_exec_t {};
 }
 
 
-#if defined(LINALG_ENABLE_KOKKOS) || defined(LINALG_ENABLE_KOKKOS_DEFAULT)
+#if defined(LINALG_ENABLE_KOKKOS) && defined(LINALG_ENABLE_KOKKOS_DEFAULT)
 #include <experimental/__p1673_bits/kokkos-kernels/exec_policy_wrapper_kk.hpp>
 #endif
 

tpl-implementations/include/experimental/__p1673_bits/kokkos-kernels/blas1_idx_abs_max_kk.hpp

@@ -0,0 +1,24 @@
+
+#ifndef LINALG_TPLIMPLEMENTATIONS_INCLUDE_EXPERIMENTAL_P1673_BITS_KOKKOSKERNELS_IDX_ABS_MAX_HPP_
+#define LINALG_TPLIMPLEMENTATIONS_INCLUDE_EXPERIMENTAL_P1673_BITS_KOKKOSKERNELS_IDX_ABS_MAX_HPP_
+
+#include <KokkosBlas1_iamax.hpp>
+
+namespace KokkosKernelsSTD {
+
+template<class ExecSpace,
+         class ElementType,
+         std::experimental::extents<>::size_type ext0,
+         class Layout,
+         class Accessor>
+auto idx_abs_max(kokkos_exec<ExecSpace>,
+		 std::experimental::mdspan<ElementType, std::experimental::extents<ext0>, Layout, Accessor> v)
+{
+  // note that -1 here, this is related to:
+  // https://github.com/kokkos/stdBLAS/issues/114
+
+  return KokkosBlas::iamax(Impl::mdspan_to_view(v))-1;
+}
+
+}
+#endif

tpl-implementations/include/experimental/linalg_kokkoskernels

@@ -5,4 +5,5 @@
 #include "__p1673_bits/kokkos-kernels/blas1_dot_kk.hpp"
 #include "__p1673_bits/kokkos-kernels/blas1_add_kk.hpp"
 #include "__p1673_bits/kokkos-kernels/blas1_scale_kk.hpp"
+#include "__p1673_bits/kokkos-kernels/blas1_idx_abs_max_kk.hpp"
 #include "__p1673_bits/kokkos-kernels/blas2_matrix_vector_product_kk.hpp"