[CK_TILE] add generic_permute (#1607)

include/ck_tile/host/reference/reference_permute.hpp

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2018-2023, Advanced Micro Devices, Inc. All rights reserved.
+
+#pragma once
+
+#include "ck_tile/core.hpp"
+#include "ck_tile/host/host_tensor.hpp"
+#include <thread>
+#include <numeric>
+#include <functional>
+
+namespace ck_tile {
+
+/*
+    this will do permute + contiguous like functionality in pytorch
+*/
+template <typename DataType>
+CK_TILE_HOST void
+reference_permute(const HostTensor<DataType>& x, HostTensor<DataType>& y, std::vector<index_t> dims)
+{
+    const auto x_len = x.mDesc.get_lengths();
+    const auto y_len = y.mDesc.get_lengths();
+    assert(x_len.size() == y_len.size());
+    index_t rank     = x_len.size();
+    const auto x_elm = std::accumulate(x_len.begin(), x_len.end(), 1, std::multiplies<index_t>());
+    const auto y_elm = std::accumulate(y_len.begin(), y_len.end(), 1, std::multiplies<index_t>());
+    assert(x_elm == y_elm);
+    (void)y_elm;
+
+    auto f = [&](auto i_element) {
+        std::vector<size_t> y_coord = [&]() {
+            std::vector<size_t> tmp(rank, 0);
+            size_t r = i_element;
+            for(index_t i = rank - 1; i >= 0; i--)
+            {
+                tmp[i] = r % y_len[i];
+                r      = r / y_len[i];
+            }
+            return tmp;
+        }();
+
+        std::vector<size_t> x_coord = [&]() {
+            std::vector<size_t> tmp(rank, 0);
+            for(index_t i = 0; i < rank; i++)
+            {
+                tmp[dims[i]] = y_coord[i];
+            }
+            return tmp;
+        }();
+
+        // do permute
+        y(y_coord) = x(x_coord);
+    };
+
+    make_ParallelTensorFunctor(f, x_elm)(std::thread::hardware_concurrency());
+}
+} // namespace ck_tile