[luci/pass] Introduce ArrayIndex helper

Let's introduce Array4DIndex to help calculating 4D array index.

ONE-DCO-Signed-off-by: Dayoung Lee <dayoung.lee@samsung.com>

compiler/luci/pass/src/helpers/ArrayIndex.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2025 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ArrayIndex.h"
+
+#include <cassert>
+
+namespace luci
+{
+
+Array4DIndex::Array4DIndex(uint32_t D0, uint32_t D1, uint32_t D2, uint32_t D3)
+  : _dim{D0, D1, D2, D3}
+{
+  assert(D0 > 0 && D1 > 0 && D2 > 0 && D3 > 0);
+
+  _strides[3] = 1;
+  _strides[2] = D3;
+  _strides[1] = D3 * D2;
+  _strides[0] = D3 * D2 * D1;
+
+  for (int i = 0; i < 4; ++i)
+  {
+    assert(_strides[i] > 0);
+  }
+}
+uint32_t Array4DIndex::operator()(uint32_t i0, uint32_t i1, uint32_t i2, uint32_t i3) const
+{
+  assert(i0 < _dim[0] && i1 < _dim[1] && i2 < _dim[2] && i3 < _dim[3]);
+  return i0 * _strides[0] + i1 * _strides[1] + i2 * _strides[2] + i3 * _strides[3];
+}
+
+uint32_t Array4DIndex::size(void) const { return _strides[3]; }
+uint32_t Array4DIndex::stride(uint32_t axis) const { return _strides[axis]; }
+
+} // namespace luci

compiler/luci/pass/src/helpers/ArrayIndex.h

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+/*
+ * Copyright (c) 2025 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __LUCI_ARRAY_INDEX_H__
+#define __LUCI_ARRAY_INDEX_H__
+
+#include <cstdint>
+
+namespace luci
+{
+
+/**
+ * @brief Index class for 4D tensor (NHWC) to calculate linear index from multi-dimensional indices.
+ */
+class Array4DIndex
+{
+public:
+  Array4DIndex(uint32_t N, uint32_t H, uint32_t W, uint32_t D);
+  /**
+   * @brief Calculate linear index from multi-dimensional indices.
+   */
+  uint32_t operator()(uint32_t n, uint32_t h, uint32_t w, uint32_t d) const;
+  /**
+   * @brief Get total number of elements in the tensor.
+   */
+  uint32_t size(void) const;
+  /**
+   * @brief Get stride of the given axis.
+   */
+  uint32_t stride(uint32_t axis) const;
+
+protected:
+  uint32_t _dim[4];
+  uint32_t _strides[4];
+};
+
+} // namespace luci
+
+#endif // __LUCI_ARRAY_INDEX_H__

compiler/luci/pass/src/helpers/ArrayIndex.test.cpp

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+/*
+ * Copyright (c) 2025 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ArrayIndex.h"
+
+#include <gtest/gtest.h>
+
+TEST(LuciPassHelpersArrayIndex, array_index_4d)
+{
+  luci::Array4DIndex idx(5, 4, 3, 2);
+
+  EXPECT_EQ(idx.rank(), 4);
+
+  EXPECT_EQ(idx(0, 0, 0, 0), 0);
+
+  EXPECT_EQ(idx(1, 0, 0, 0), idx.stride(0));
+  EXPECT_EQ(idx(0, 1, 0, 0), idx.stride(1));
+  EXPECT_EQ(idx(0, 0, 1, 0), idx.stride(2));
+  EXPECT_EQ(idx(0, 0, 0, 1), idx.stride(3));
+
+  EXPECT_EQ(idx(4, 3, 2, 1), 4 * 4 * 3 * 2 + 3 * 3 * 2 + 2 * 2 + 1);
+}
+
+TEST(LuciPassHelpersArrayIndex, array_index_4d_NEG)
+{
+  ASSERT_THROW(luci::Array4DIndex idx(5, 4, 3, -1));
+}