/* Copyright 2019 The TensorFlow Authors. 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.
==============================================================================*/
// WARNING: Users of TensorFlow Lite should not include this file directly, but
// should instead include "third_party/tensorflow/lite/c/common.h".
// Only the TensorFlow Lite implementation itself should include this file
// directly.

/// This file defines common C types and APIs for implementing operations,
/// delegates and other constructs in TensorFlow Lite. The actual operations and
/// delegates can be defined using C++, but the interface between the
/// interpreter and the operations are C.
///
/// Summary of abstractions:
/// * `TF_LITE_ENSURE` - self-sufficient error checking
/// * `TfLiteStatus` - status reporting
/// * `TfLiteIntArray` - stores tensor shapes (dims),
/// * `TfLiteContext` - allows an op to access the tensors
/// * `TfLiteTensor` - tensor (a multidimensional array)
/// * `TfLiteNode` - a single node or operation
/// * `TfLiteRegistration` - the implementation of a conceptual operation.
/// * `TfLiteDelegate` - allows delegation of nodes to alternative backends.
///
/// Some abstractions in this file are created and managed by Interpreter.
///
/// NOTE: The order of values in these structs are "semi-ABI stable". New values
/// should be added only to the end of structs and never reordered.
///
// clang-format off
// NOLINTBEGIN(whitespace/line_length)
/// \note Users of TensorFlow Lite should use
/// \code
/// #include "tensorflow/lite/c/common.h"
/// \endcode
/// to access the APIs documented on this page.
// NOLINTEND(whitespace/line_length)
// clang-format on

// IWYU pragma: private, include "third_party/tensorflow/lite/c/common.h"

#ifndef TENSORFLOW_LITE_CORE_C_COMMON_H_
#define TENSORFLOW_LITE_CORE_C_COMMON_H_

#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

#include "tensorflow/lite/core/c/c_api_types.h"  // IWYU pragma: export

#ifdef __cplusplus
extern "C" {
#endif  // __cplusplus

// clang-format off
// NOLINTBEGIN(whitespace/line_length)
/** \defgroup common lite/c/common.h
 *  @{
 */
// NOLINTEND(whitespace/line_length)
// clang-format on

/// The list of external context types known to TF Lite. This list exists solely
/// to avoid conflicts and to ensure ops can share the external contexts they
/// need. Access to the external contexts is controlled by one of the
/// corresponding support files.
typedef enum TfLiteExternalContextType {
  kTfLiteEigenContext = 0,       /// include eigen_support.h to use.
  kTfLiteGemmLowpContext = 1,    /// include gemm_support.h to use.
  kTfLiteEdgeTpuContext = 2,     /// Placeholder for Edge TPU support.
  kTfLiteCpuBackendContext = 3,  /// include cpu_backend_context.h to use.
  kTfLiteLiteRtBufferContext =
      4,  /// include external_litert_buffer_context.h to use.
  kTfLiteMaxExternalContexts = 5
} TfLiteExternalContextType;

// Forward declare so dependent structs and methods can reference these types
// prior to the struct definitions.
struct TfLiteContext;
struct TfLiteDelegate;
struct TfLiteRegistration;
struct TfLiteOpaqueDelegateBuilder;

/// An external context is a collection of information unrelated to the TF Lite
/// framework, but useful to a subset of the ops. TF Lite knows very little
/// about the actual contexts, but it keeps a list of them, and is able to
/// refresh them if configurations like the number of recommended threads
/// change.
typedef struct TfLiteExternalContext {
  TfLiteExternalContextType type;
  TfLiteStatus (*Refresh)(struct TfLiteContext* context);
} TfLiteExternalContext;

// LINT.IfChange(optional_tensor)
#define kTfLiteOptionalTensor (-1)
// LINT.ThenChange(//tensorflow/compiler/mlir/lite/flatbuffer_export.cc:optional_tensor)

/// Fixed size list of integers. Used for dimensions and inputs/outputs tensor
/// indices
typedef struct TfLiteIntArray {
  int size;

#if defined(_MSC_VER)
  // Context for why this is needed is in http://b/189926408#comment21
  int data[1];
#elif (!defined(__clang__) && defined(__GNUC__) && __GNUC__ == 6 && \
       __GNUC_MINOR__ >= 1) ||                                      \
    defined(HEXAGON) ||                                             \
    (defined(__clang__) && __clang_major__ == 7 && __clang_minor__ == 1)
  // gcc 6.1+ have a bug where flexible members aren't properly handled
  // https://github.com/google/re2/commit/b94b7cd42e9f02673cd748c1ac1d16db4052514c
  int data[0];
#else
  int data[];
#endif
} TfLiteIntArray;

/// Given the size (number of elements) in a TfLiteIntArray, calculate its size
/// in bytes.
size_t TfLiteIntArrayGetSizeInBytes(int size);

#ifndef TF_LITE_STATIC_MEMORY
/// Create a array of a given `size` (uninitialized entries).
/// This returns a pointer, that you must free using TfLiteIntArrayFree().
TfLiteIntArray* TfLiteIntArrayCreate(int size);
#endif

/// Check if two intarrays are equal. Returns 1 if they are equal, 0 otherwise.
int TfLiteIntArrayEqual(const TfLiteIntArray* a, const TfLiteIntArray* b);

/// Check if an intarray equals an array. Returns 1 if equals, 0 otherwise.
int TfLiteIntArrayEqualsArray(const TfLiteIntArray* a, int b_size,
                              const int b_data[]);

#ifndef TF_LITE_STATIC_MEMORY
/// Create a copy of an array passed as `src`.
/// You are expected to free memory with TfLiteIntArrayFree
TfLiteIntArray* TfLiteIntArrayCopy(const TfLiteIntArray* src);

/// Free memory of array `a`.
void TfLiteIntArrayFree(TfLiteIntArray* a);
#endif  // TF_LITE_STATIC_MEMORY

/// Fixed size list of floats. Used for per-channel quantization.
typedef struct TfLiteFloatArray {
  int size;
#if defined(_MSC_VER)
  // Context for why this is needed is in http://b/189926408#comment21
  float data[1];
#elif (!defined(__clang__) && defined(__GNUC__) && __GNUC__ == 6 && \
       __GNUC_MINOR__ >= 1) ||                                      \
    defined(HEXAGON) ||                                             \
    (defined(__clang__) && __clang_major__ == 7 && __clang_minor__ == 1)
  // gcc 6.1+ have a bug where flexible members aren't properly handled
  // https://github.com/google/re2/commit/b94b7cd42e9f02673cd748c1ac1d16db4052514c
  float data[0];
#else
  float data[];
#endif
} TfLiteFloatArray;

/// Given the size (number of elements) in a TfLiteFloatArray, calculate its
/// size in bytes.
int TfLiteFloatArrayGetSizeInBytes(int size);

#ifndef TF_LITE_STATIC_MEMORY
/// Create a array of a given `size` (uninitialized entries).
/// This returns a pointer, that you must free using TfLiteFloatArrayFree().
TfLiteFloatArray* TfLiteFloatArrayCreate(int size);

/// Create a copy of an array passed as `src`.
/// You are expected to free memory with TfLiteFloatArrayFree.
TfLiteFloatArray* TfLiteFloatArrayCopy(const TfLiteFloatArray* src);

/// Free memory of array `a`.
void TfLiteFloatArrayFree(TfLiteFloatArray* a);
#endif  // TF_LITE_STATIC_MEMORY

// Since we must not depend on any libraries, define a minimal subset of
// error macros while avoiding names that have pre-conceived meanings like
// assert and check.

// Try to make all reporting calls through TF_LITE_KERNEL_LOG rather than
// calling the context->ReportError function directly, so that message strings
// can be stripped out if the binary size needs to be severely optimized.
#ifndef TF_LITE_STRIP_ERROR_STRINGS
#define TF_LITE_KERNEL_LOG(context, ...)            \
  do {                                              \
    (context)->ReportError((context), __VA_ARGS__); \
  } while (false)

#define TF_LITE_MAYBE_KERNEL_LOG(context, ...)        \
  do {                                                \
    if ((context) != nullptr) {                       \
      (context)->ReportError((context), __VA_ARGS__); \
    }                                                 \
  } while (false)
#else  // TF_LITE_STRIP_ERROR_STRINGS
#define ARGS_UNUSED(...) (void)sizeof(#__VA_ARGS__)
#define TF_LITE_KERNEL_LOG(context, ...) ARGS_UNUSED(__VA_ARGS__)
#define TF_LITE_MAYBE_KERNEL_LOG(context, ...) ARGS_UNUSED(__VA_ARGS__)
#endif  // TF_LITE_STRIP_ERROR_STRINGS

/// Check whether value is true, and if not return kTfLiteError from
/// the current function (and report the error string msg).
#define TF_LITE_ENSURE_MSG(context, value, ...)                \
  do {                                                         \
    if (!(value)) {                                            \
      TF_LITE_KERNEL_LOG((context), __FILE__ " " __VA_ARGS__); \
      return kTfLiteError;                                     \
    }                                                          \
  } while (0)

/// Check whether the value `a` is true, and if not return kTfLiteError from
/// the current function, while also reporting the location of the error.
#define TF_LITE_ENSURE(context, a)                                      \
  do {                                                                  \
    if (!(a)) {                                                         \
      TF_LITE_KERNEL_LOG((context), "%s:%d %s was not true.", __FILE__, \
                         __LINE__, #a);                                 \
      return kTfLiteError;                                              \
    }                                                                   \
  } while (0)

#define TF_LITE_ENSURE_STATUS(a) \
  do {                           \
    const TfLiteStatus s = (a);  \
    if (s != kTfLiteOk) {        \
      return s;                  \
    }                            \
  } while (0)

/// Check whether the value `a == b` is true, and if not return kTfLiteError
/// from the current function, while also reporting the location of the error.
/// `a` and `b` may be evaluated more than once, so no side effects or
/// extremely expensive computations should be done.
///
/// NOTE: Use TF_LITE_ENSURE_TYPES_EQ if comparing TfLiteTypes.
#define TF_LITE_ENSURE_EQ(context, a, b)                                   \
  do {                                                                     \
    if ((a) != (b)) {                                                      \
      TF_LITE_KERNEL_LOG((context), "%s:%d %s != %s (%d != %d)", __FILE__, \
                         __LINE__, #a, #b, (a), (b));                      \
      return kTfLiteError;                                                 \
    }                                                                      \
  } while (0)

#define TF_LITE_ENSURE_TYPES_EQ(context, a, b)                             \
  do {                                                                     \
    if ((a) != (b)) {                                                      \
      TF_LITE_KERNEL_LOG((context), "%s:%d %s != %s (%s != %s)", __FILE__, \
                         __LINE__, #a, #b, TfLiteTypeGetName(a),           \
                         TfLiteTypeGetName(b));                            \
      return kTfLiteError;                                                 \
    }                                                                      \
  } while (0)

#define TF_LITE_ENSURE_NEAR(context, a, b, epsilon)                          \
  do {                                                                       \
    auto delta = ((a) > (b)) ? ((a) - (b)) : ((b) - (a));                    \
    if (delta > epsilon) {                                                   \
      TF_LITE_KERNEL_LOG((context), "%s:%d %s not near %s (%f != %f)",       \
                         __FILE__, __LINE__, #a, #b, static_cast<double>(a), \
                         static_cast<double>(b));                            \
      return kTfLiteError;                                                   \
    }                                                                        \
  } while (0)

#define TF_LITE_ENSURE_OK(context, status) \
  do {                                     \
    const TfLiteStatus s = (status);       \
    if ((s) != kTfLiteOk) {                \
      return s;                            \
    }                                      \
  } while (0)

// `std::unreachable` not available until CC23.
#ifdef __GNUC__  // GCC, Clang, ICC

#define TFL_UNREACHABLE() (__builtin_unreachable())

#elif defined(_MSC_VER)  // MSVC

#define TFL_UNREACHABLE() (__assume(false))

#endif

/// Single-precision complex data type compatible with the C99 definition.
typedef struct TfLiteComplex64 {
  float re, im;  /// real and imaginary parts, respectively.
} TfLiteComplex64;

/// Double-precision complex data type compatible with the C99 definition.
typedef struct TfLiteComplex128 {
  double re, im;  /// real and imaginary parts, respectively.
} TfLiteComplex128;

/// Half precision data type compatible with the C99 definition.
typedef struct TfLiteFloat16 {
  uint16_t data;
} TfLiteFloat16;

/// bfloat16 data type compatible with the Google Brain definition.
/// https://cloud.google.com/tpu/docs/bfloat16.
/// This provides 1 bit of sign, 8 bits of exponent, and 7 bits of mantissa.
typedef struct TfLiteBFloat16 {
  uint16_t data;
} TfLiteBFloat16;

/// Return the name of a given type, for error reporting purposes.
const char* TfLiteTypeGetName(TfLiteType type);

/// SupportedQuantizationTypes.
typedef enum TfLiteQuantizationType : int {
  /// No quantization.
  kTfLiteNoQuantization = 0,
  /// Affine quantization (with support for per-channel quantization).
  /// Corresponds to TfLiteAffineQuantization.
  kTfLiteAffineQuantization = 1,
} TfLiteQuantizationType;

/// Structure specifying the quantization used by the tensor, if-any.
typedef struct TfLiteQuantization {
  /// The type of quantization held by params.
  TfLiteQuantizationType type;
  /// Holds an optional reference to a quantization param structure. The actual
  /// type depends on the value of the `type` field (see the comment there for
  /// the values and corresponding types).
  void* params;
} TfLiteQuantization;

/// Parameters for asymmetric quantization across a dimension (i.e per output
/// channel quantization).
/// quantized_dimension specifies which dimension the scales and zero_points
/// correspond to.
/// For a particular value in quantized_dimension, quantized values can be
/// converted back to float using:
///     `real_value = scale * (quantized_value - zero_point)`
typedef struct TfLiteAffineQuantization {
  TfLiteFloatArray* scale;
  TfLiteIntArray* zero_point;
  int32_t quantized_dimension;
} TfLiteAffineQuantization;

/// A union of pointers that points to memory for a given tensor.
///
/// Do not access these members directly, if possible, use
/// `GetTensorData<TYPE>(tensor)` instead, otherwise only access `.data`, as
/// other members are deprecated.
typedef union TfLitePtrUnion {
  int32_t* i32;
  uint32_t* u32;
  int64_t* i64;
  uint64_t* u64;
  float* f;
  TfLiteFloat16* f16;
  TfLiteBFloat16* bf16;
  double* f64;
  char* raw;
  const char* raw_const;
  uint8_t* uint8;
  bool* b;
  int16_t* i16;
  uint16_t* ui16;
  TfLiteComplex64* c64;
  TfLiteComplex128* c128;
  int8_t* int8;
  /// Only use this member.
  void* data;
} TfLitePtrUnion;

/// Memory allocation strategies.
///  * `kTfLiteMmapRo`: Read-only memory-mapped data, or data externally
///        allocated.
///  * `kTfLiteArenaRw`: Arena allocated with no guarantees about persistence,
///        and available during eval.
///  * `kTfLiteArenaRwPersistent`: Arena allocated but persistent across eval,
///  and only available during eval.
///  * `kTfLiteDynamic`: Allocated during eval, or for string tensors.
///  * `kTfLitePersistentRo`: Allocated and populated during prepare. This is
///        useful for tensors that can be computed during prepare and treated
///        as constant inputs for downstream ops (also in prepare).
///  * `kTfLiteCustom`: Custom memory allocation provided by the user. See
///        TfLiteCustomAllocation below.
///  * `kTfLiteVariantObject`: Allocation is an arbitrary type-erased C++
///  object.
///        Allocation and deallocation are done through `new` and `delete`.
typedef enum TfLiteAllocationType {
  kTfLiteMemNone = 0,
  kTfLiteMmapRo,
  kTfLiteArenaRw,
  kTfLiteArenaRwPersistent,
  kTfLiteDynamic,
  kTfLitePersistentRo,
  kTfLiteCustom,
  kTfLiteVariantObject,
} TfLiteAllocationType;

/// Memory allocation strategies.
///
/// TfLiteAllocationType values have been overloaded to mean more than their
/// original intent. This enum should only be used to document the allocation
/// strategy used by a tensor for it data.
typedef enum TfLiteAllocationStrategy {
  kTfLiteAllocationStrategyUnknown,
  kTfLiteAllocationStrategyNone,    /// No data is allocated.
  kTfLiteAllocationStrategyMMap,    /// Data is mmaped.
  kTfLiteAllocationStrategyArena,   /// Handled by the arena.
  kTfLiteAllocationStrategyMalloc,  /// Uses `malloc`/`free`.
  kTfLiteAllocationStrategyNew      /// Uses `new[]`/`delete[]`.
} TfLiteAllocationStrategy;

/// Describes how stable a tensor attribute is with regards to an interpreter
/// runs.
typedef enum TfLiteRunStability {
  kTfLiteRunStabilityUnknown,
  kTfLiteRunStabilityUnstable,   /// May change at any time.
  kTfLiteRunStabilitySingleRun,  /// Will stay the same for one run.
  kTfLiteRunStabilityAcrossRuns  /// Will stay the same across all runs.
} TfLiteRunStability;

/// Describes the steps of a TFLite operation life cycle.
typedef enum TfLiteRunStep {
  kTfLiteRunStepUnknown,
  kTfLiteRunStepInit,
  kTfLiteRunStepPrepare,
  kTfLiteRunStepEval
} TfLiteRunStep;

/// The delegates should use zero or positive integers to represent handles.
/// -1 is reserved from unallocated status.
typedef int TfLiteBufferHandle;
enum {
  kTfLiteNullBufferHandle = -1,
};

/// Metadata to encode each dimension in a sparse tensor.
typedef struct TfLiteDimensionMetadata {
  TfLiteDimensionType format;
  int dense_size;
  TfLiteIntArray* array_segments;
  TfLiteIntArray* array_indices;
} TfLiteDimensionMetadata;

/// Parameters used to encode a sparse tensor. For detailed explanation of each
/// field please refer to lite/schema/schema.fbs.
typedef struct TfLiteSparsity {
  TfLiteIntArray* traversal_order;
  TfLiteIntArray* block_map;
  TfLiteDimensionMetadata* dim_metadata;
  int dim_metadata_size;
} TfLiteSparsity;

/// Defines a custom memory allocation not owned by the runtime.
/// `data` should be aligned to kDefaultTensorAlignment defined in
/// lite/util.h. (Currently 64 bytes)
/// NOTE: See `Interpreter::SetCustomAllocationForTensor` for details on usage.
typedef struct TfLiteCustomAllocation {
  void* data;
  size_t bytes;
} TfLiteCustomAllocation;

/// The flags used in `Interpreter::SetCustomAllocationForTensor`.
/// Note that this is a bitmask, so the values should be 1, 2, 4, 8, ...etc.
typedef enum TfLiteCustomAllocationFlags {
  kTfLiteCustomAllocationFlagsNone = 0,
  /// Skips checking whether allocation.data points to an aligned buffer as
  /// expected by the TFLite runtime.
  /// NOTE: Setting this flag can cause crashes when calling Invoke().
  /// Use with caution.
  kTfLiteCustomAllocationFlagsSkipAlignCheck = 1,
} TfLiteCustomAllocationFlags;

enum { kTfLiteNoBufferIdentifier = SIZE_MAX };

/// A tensor in the interpreter system which is a wrapper around a buffer of
/// data including a dimensionality (or NULL if not currently defined).
#ifndef TF_LITE_STATIC_MEMORY
typedef struct TfLiteTensor {
  /// The data type specification for data stored in `data`. This affects
  /// what member of `data` union should be used.
  TfLiteType type;
  /// A union of data pointers. The appropriate type should be used for a typed
  /// tensor based on `type`.
  TfLitePtrUnion data;
  /// A pointer to a structure representing the dimensionality interpretation
  /// that the buffer should have. NOTE: the product of elements of `dims`
  /// and the element datatype size should be equal to `bytes` below.
  TfLiteIntArray* dims;
  /// Quantization information.
  TfLiteQuantizationParams params;
  /// How memory is mapped
  ///  kTfLiteMmapRo: Memory mapped read only.
  ///  i.e. weights
  ///  kTfLiteArenaRw: Arena allocated read write memory
  ///  (i.e. temporaries, outputs).
  TfLiteAllocationType allocation_type;
  /// The number of bytes required to store the data of this Tensor. I.e.
  /// (bytes of each element) * dims[0] * ... * dims[n-1].  For example, if
  /// type is kTfLiteFloat32 and dims = {3, 2} then
  /// bytes = sizeof(float) * 3 * 2 = 4 * 3 * 2 = 24.
  size_t bytes;

  /// An opaque pointer to a tflite::MMapAllocation
  const void* allocation;

  /// Null-terminated name of this tensor.
  const char* name;

  /// The delegate which knows how to handle `buffer_handle`.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  struct TfLiteDelegate* delegate;

  /// An integer buffer handle that can be handled by `delegate`.
  /// The value is valid only when delegate is not null.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteBufferHandle buffer_handle;

  /// If the delegate uses its own buffer (e.g. GPU memory), the delegate is
  /// responsible to set data_is_stale to true.
  /// `delegate->CopyFromBufferHandle` can be called to copy the data from
  /// delegate buffer.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  bool data_is_stale;

  /// True if the tensor is a variable.
  bool is_variable;

  /// Quantization information. Replaces params field above.
  TfLiteQuantization quantization;

  /// Parameters used to encode a sparse tensor.
  /// This is optional. The field is NULL if a tensor is dense.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteSparsity* sparsity;

  /// Optional. Encodes shapes with unknown dimensions with -1. This field is
  /// only populated when unknown dimensions exist in a read-write tensor (i.e.
  /// an input or output tensor). (e.g.  `dims` contains [1, 1, 1, 3] and
  /// `dims_signature` contains [1, -1, -1, 3]).  If no unknown dimensions exist
  /// then `dims_signature` is either null, or set to an empty array.  Note that
  /// this field only exists when TF_LITE_STATIC_MEMORY is not defined.
  const TfLiteIntArray* dims_signature;
} TfLiteTensor;

/// A structure representing an instance of a node.
/// This structure only exhibits the inputs, outputs, user defined data and some
/// node properties (like statefulness), not other features like the type.
typedef struct TfLiteNode {
  /// Inputs to this node expressed as indices into the simulator's tensors.
  TfLiteIntArray* inputs;

  /// Outputs to this node expressed as indices into the simulator's tensors.
  TfLiteIntArray* outputs;

  /// intermediate tensors to this node expressed as indices into the
  /// simulator's tensors.
  TfLiteIntArray* intermediates;

  /// Temporary tensors uses during the computations. This usually contains no
  /// tensors, but ops are allowed to change that if they need scratch space of
  /// any sort.
  TfLiteIntArray* temporaries;

  /// Opaque data provided by the node implementer through `Registration.init`.
  void* user_data;

  /// Opaque data provided to the node if the node is a builtin. This is usually
  /// a structure defined in builtin_op_data.h
  void* builtin_data;

  /// Custom initial data. This is the opaque data provided in the flatbuffer.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  const void* custom_initial_data;
  int custom_initial_data_size;

  /// The pointer to the delegate. This is non-null only when the node is
  /// created by calling `interpreter.ModifyGraphWithDelegate`.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  struct TfLiteDelegate* delegate;

  /// Whether this op might have side effect (e.g. stateful op).
  bool might_have_side_effect;
} TfLiteNode;
#else   // defined(TF_LITE_STATIC_MEMORY)?
// NOTE: This flag is opt-in only at compile time.
//
// Specific reduced TfLiteTensor struct for TF Micro runtime. This struct
// contains only the minimum fields required to initialize and prepare a micro
// inference graph. The fields in this struct have been ordered from
// largest-to-smallest for optimal struct sizeof.
//
// This struct does not use:
// - allocation
// - buffer_handle
// - data_is_stale
// - delegate
// - dims_signature
// - name
// - sparsity
typedef struct TfLiteTensor {
  // TODO(b/155784997): Consider consolidating these quantization fields:
  // Quantization information. Replaces params field above.
  TfLiteQuantization quantization;

  // Quantization information.
  TfLiteQuantizationParams params;

  // A union of data pointers. The appropriate type should be used for a typed
  // tensor based on `type`.
  TfLitePtrUnion data;

  // A pointer to a structure representing the dimensionality interpretation
  // that the buffer should have. NOTE: the product of elements of `dims`
  // and the element datatype size should be equal to `bytes` below.
  TfLiteIntArray* dims;

  // The number of bytes required to store the data of this Tensor. I.e.
  // (bytes of each element) * dims[0] * ... * dims[n-1].  For example, if
  // type is kTfLiteFloat32 and dims = {3, 2} then
  // bytes = sizeof(float) * 3 * 2 = 4 * 3 * 2 = 24.
  size_t bytes;

  // The data type specification for data stored in `data`. This affects
  // what member of `data` union should be used.
  TfLiteType type;

  // How memory is mapped
  //  kTfLiteMmapRo: Memory mapped read only.
  //  i.e. weights
  //  kTfLiteArenaRw: Arena allocated read write memory
  //  (i.e. temporaries, outputs).
  TfLiteAllocationType allocation_type;

  // True if the tensor is a variable.
  bool is_variable;
} TfLiteTensor;

// Specific reduced TfLiteNode struct for TF Micro runtime. This struct contains
// only the minimum fields required to represent a node.
//
// This struct does not use:
// - delegate
// - intermediates
// - temporaries
typedef struct TfLiteNode {
  // Inputs to this node expressed as indices into the simulator's tensors.
  TfLiteIntArray* inputs;

  // Outputs to this node expressed as indices into the simulator's tensors.
  TfLiteIntArray* outputs;

  // intermediate tensors to this node expressed as indices into the simulator's
  // tensors.
  TfLiteIntArray* intermediates;

  // Opaque data provided by the node implementer through `Registration.init`.
  void* user_data;

  // Opaque data provided to the node if the node is a builtin. This is usually
  // a structure defined in builtin_op_data.h
  void* builtin_data;

  // Custom initial data. This is the opaque data provided in the flatbuffer.
  //
  // WARNING: This is an experimental interface that is subject to change.
  const void* custom_initial_data;
  int custom_initial_data_size;
} TfLiteNode;
#endif  // TF_LITE_STATIC_MEMORY

/// Light-weight tensor struct for TF Micro runtime. Provides the minimal amount
/// of information required for a kernel to run during TfLiteRegistration::Eval.
// TODO(b/160955687): Move this field into TF_LITE_STATIC_MEMORY when TFLM
// builds with this flag by default internally.
typedef struct TfLiteEvalTensor {
  /// A union of data pointers. The appropriate type should be used for a typed
  /// tensor based on `type`.
  TfLitePtrUnion data;

  /// A pointer to a structure representing the dimensionality interpretation
  /// that the buffer should have.
  TfLiteIntArray* dims;

  /// The data type specification for data stored in `data`. This affects
  /// what member of `data` union should be used.
  TfLiteType type;
} TfLiteEvalTensor;

#ifndef TF_LITE_STATIC_MEMORY
/// Free data memory of tensor `t`.
void TfLiteTensorDataFree(TfLiteTensor* t);

/// Free quantization data.
void TfLiteQuantizationFree(TfLiteQuantization* quantization);

/// Free sparsity parameters.
void TfLiteSparsityFree(TfLiteSparsity* sparsity);

/// Free memory of tensor `t`.
void TfLiteTensorFree(TfLiteTensor* t);

/// Set all of a tensor's fields (and free any previously allocated data).
void TfLiteTensorReset(TfLiteType type, const char* name, TfLiteIntArray* dims,
                       TfLiteQuantizationParams quantization, char* buffer,
                       size_t size, TfLiteAllocationType allocation_type,
                       const void* allocation, bool is_variable,
                       TfLiteTensor* tensor);

/// Copies the contents of `src` in `dst`.
/// Function does nothing if either `src` or `dst` is passed as nullptr and
/// return `kTfLiteOk`.
/// Returns `kTfLiteError` if `src` and `dst` doesn't have matching data size.
/// Note function copies contents, so it won't create new data pointer
/// or change allocation type.
/// All Tensor related properties will be copied from `src` to `dst` like
/// quantization, sparsity, ...
TfLiteStatus TfLiteTensorCopy(const TfLiteTensor* src, TfLiteTensor* dst);

/// Change the size of the memory block owned by `tensor` to `num_bytes`.
/// Tensors with allocation types other than `kTfLiteDynamic` will be ignored
/// and a `kTfLiteOk` will be returned. `tensor`'s internal data buffer will be
/// assigned a pointer which can safely be passed to free or realloc if
/// `num_bytes` is zero. If `preserve_data` is true, tensor data will be
/// unchanged in the range from the start of the region up to the minimum of the
/// old and new sizes. In the case of NULL tensor, or an error allocating new
/// memory, returns `kTfLiteError`.
TfLiteStatus TfLiteTensorResizeMaybeCopy(size_t num_bytes, TfLiteTensor* tensor,
                                         bool preserve_data);

/// Change the size of the memory block owned by `tensor` to `num_bytes`.
/// Tensors with allocation types other than `kTfLiteDynamic` will be ignored
/// and a `kTfLiteOk` will be returned. `tensor`'s internal data buffer will be
/// assigned a pointer which can safely be passed to free or realloc if
/// `num_bytes` is zero. Tensor data will be unchanged in the range from the
/// start of the region up to the minimum of the old and new sizes. In the case
/// of NULL tensor, or an error allocating new memory, returns `kTfLiteError`.
TfLiteStatus TfLiteTensorRealloc(size_t num_bytes, TfLiteTensor* tensor);
#endif  // TF_LITE_STATIC_MEMORY

/// WARNING: This is an experimental interface that is subject to change.
///
/// Currently, TfLiteDelegateParams has to be allocated in a way that it's
/// trivially destructable. It will be stored as `builtin_data` field in
/// `TfLiteNode` of the delegate node.
///
/// See also the `CreateDelegateParams` function in `interpreter.cc` details.
typedef struct TfLiteDelegateParams {
  struct TfLiteDelegate* delegate;
  TfLiteIntArray* nodes_to_replace;
  TfLiteIntArray* input_tensors;
  TfLiteIntArray* output_tensors;
} TfLiteDelegateParams;

/// WARNING: This is an experimental interface that is subject to change.
///
/// Currently, TfLiteOpaqueDelegateParams has to be allocated in a way that it's
/// trivially destructable. It will be stored as `builtin_data` field in
/// `TfLiteNode` of the delegate node.
///
/// See also the `CreateOpaqueDelegateParams` function in `subgraph.cc`
/// details.
typedef struct TfLiteOpaqueDelegateParams {
  TfLiteOpaqueDelegate* delegate;
  void* delegate_data;
  TfLiteIntArray* nodes_to_replace;
  TfLiteIntArray* input_tensors;
  TfLiteIntArray* output_tensors;
} TfLiteOpaqueDelegateParams;

/// `TfLiteContext` allows an op to access the tensors.
///
/// `TfLiteContext` is a struct that is created by the TF Lite runtime
/// and passed to the "methods" (C function pointers) in the
/// `TfLiteRegistration` struct that are used to define custom ops and custom
/// delegate kernels. It contains information and methods (C function pointers)
/// that can be called by the code implementing a custom op or a custom delegate
/// kernel. These methods provide access to the context in which that custom op
/// or custom delegate kernel occurs, such as access to the input and output
/// tensors for that op, as well as methods for allocating memory buffers
/// and intermediate tensors, etc.
///
/// See also `TfLiteOpaqueContext`, which is an more ABI-stable equivalent.
typedef struct TfLiteContext {
  /// Number of tensors in the context.
  size_t tensors_size;

  /// The execution plan contains a list of the node indices in execution
  /// order. execution_plan->size is the current number of nodes. And,
  /// execution_plan->data[0] is the first node that needs to be run.
  /// TfLiteDelegates can traverse the current execution plan by iterating
  /// through each member of this array and using GetNodeAndRegistration() to
  /// access details about a node. i.e.
  ///
  ///
  ///     TfLiteIntArray* execution_plan;
  ///     TF_LITE_ENSURE_STATUS(context->GetExecutionPlan(context,
  ///                                                     &execution_plan));
  ///     for (int exec_index = 0; exec_index < execution_plan->size;
  ///           exec_index++) {
  ///        int node_index = execution_plan->data[exec_index];
  ///        TfLiteNode* node;
  ///        TfLiteRegistration* reg;
  ///        context->GetNodeAndRegistration(context, node_index, &node, &reg);
  ///     }
  ///
  /// Note: the memory pointed by '`*execution_plan` is OWNED by TfLite runtime.
  /// Future calls to GetExecutionPlan invalidates earlier outputs. The
  /// following code snippet shows the issue of such an invocation pattern.
  /// After calling CheckNode, subsequent access to `plan_1st` is undefined.
  ///
  ///     void CheckNode(const TfLiteNode* node) {
  ///       ...
  ///       TfLiteIntArray* plan_2nd;
  ///       TF_LITE_ENSURE_STATUS(
  ///           context->GetExecutionPlan(context, &plan_2nd)
  ///       );
  ///       ...
  ///     }
  ///
  ///     TfLiteIntArray* plan_1st;
  ///     TF_LITE_ENSURE_STATUS(context->GetExecutionPlan(context, &plan_1st));
  ///     for (int exec_index = 0; exec_index < plan_1st->size; exec_index++) {
  ///        int node_index = plan_1st->data[exec_index];
  ///        TfLiteNode* node;
  ///        TfLiteRegistration* reg;
  ///        context->GetNodeAndRegistration(context, node_index, &node, &reg);
  ///        CheckNode(node);
  ///     }
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*GetExecutionPlan)(struct TfLiteContext* context,
                                   TfLiteIntArray** execution_plan);

  /// An array of tensors in the interpreter context (of length `tensors_size`)
  TfLiteTensor* tensors;

  /// opaque full context ptr (an opaque c++ data structure)
  void* impl_;

  /// Request memory pointer be resized. Updates dimensions on the tensor.
  /// NOTE: ResizeTensor takes ownership of newSize.
  TfLiteStatus (*ResizeTensor)(struct TfLiteContext*, TfLiteTensor* tensor,
                               TfLiteIntArray* new_size);
  /// Request that an error be reported with format string msg.
  void (*ReportError)(struct TfLiteContext*, const char* msg, ...);

  /// Add `tensors_to_add` tensors, preserving pre-existing Tensor entries.  If
  /// non-null, the value pointed to by `first_new_tensor_index` will be set to
  /// the index of the first new tensor.
  TfLiteStatus (*AddTensors)(struct TfLiteContext*, int tensors_to_add,
                             int* first_new_tensor_index);

  /// Get a Tensor node by node_index.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*GetNodeAndRegistration)(
      struct TfLiteContext*, int node_index, TfLiteNode** node,
      struct TfLiteRegistration** registration);

  /// Replace ops with one or more stub delegate operations. This function
  /// does not take ownership of `nodes_to_replace`.
  TfLiteStatus (*ReplaceNodeSubsetsWithDelegateKernels)(
      struct TfLiteContext*, struct TfLiteRegistration registration,
      const TfLiteIntArray* nodes_to_replace, struct TfLiteDelegate* delegate);

  /// Number of threads that are recommended to subsystems like gemmlowp and
  /// eigen.
  int recommended_num_threads;

  /// Access external contexts by type.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteExternalContext* (*GetExternalContext)(struct TfLiteContext*,
                                               TfLiteExternalContextType);
  /// Set the value of a external context. Does not take ownership of the
  /// pointer.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  void (*SetExternalContext)(struct TfLiteContext*, TfLiteExternalContextType,
                             TfLiteExternalContext*);

  /// Flag for allowing float16 precision for FP32 calculation.
  /// default: false.
  ///
  /// WARNING: This is an experimental API and subject to change.
  bool allow_fp32_relax_to_fp16;

  /// Pointer to the op-level profiler, if set; nullptr otherwise.
  void* profiler;

  /// Allocate persistent buffer which has the same life time as the
  /// interpreter. Returns `nullptr` on failure. The memory is allocated from
  /// heap for TFL, and from tail in TFLM. This method is only available in
  /// `Init` or `Prepare` stage.
  ///
  /// WARNING: This is an experimental interface that is subject
  /// to change.
  void* (*AllocatePersistentBuffer)(struct TfLiteContext* ctx, size_t bytes);

  /// Allocate a buffer which will be deallocated right after invoke phase.
  /// The memory is allocated from heap in TFL, and from volatile arena in TFLM.
  /// This method is only available in invoke stage.
  ///
  /// NOTE: If possible use `RequestScratchBufferInArena` method to avoid memory
  /// allocation during inference time.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*AllocateBufferForEval)(struct TfLiteContext* ctx, size_t bytes,
                                        void** ptr);

  /// Request a scratch buffer in the arena through static memory planning.
  /// This method is only available in `Prepare` stage and the buffer is
  /// allocated by the interpreter between Prepare and Eval stage. In `Eval`
  /// stage, `GetScratchBuffer` API can be used to fetch the address.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*RequestScratchBufferInArena)(struct TfLiteContext* ctx,
                                              size_t bytes, int* buffer_idx);

  /// Get the scratch buffer pointer.
  /// This method is only available in Eval stage.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  void* (*GetScratchBuffer)(struct TfLiteContext* ctx, int buffer_idx);

  /// Resize the memory pointer of the `tensor`. This method behaves the same as
  /// `ResizeTensor`, except that it makes a copy of the shape array internally
  /// so the shape array could be deallocated right afterwards.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*ResizeTensorExplicit)(struct TfLiteContext* ctx,
                                       TfLiteTensor* tensor, int dims,
                                       const int* shape);

  /// This method provides a preview of post-delegation partitioning. Each
  /// TfLiteDelegateParams in the referenced array corresponds to one instance
  /// of the delegate kernel. Example usage:
  ///
  ///     TfLiteIntArray* nodes_to_replace = ...;
  ///     TfLiteDelegateParams* params_array;
  ///     int num_partitions = 0;
  ///     TF_LITE_ENSURE_STATUS(context->PreviewDelegatePartitioning(
  ///        context, delegate, nodes_to_replace, &params_array,
  ///        &num_partitions));
  ///     for (int idx = 0; idx < num_partitions; idx++) {
  ///        const auto& partition_params = params_array[idx];
  ///        ...
  ///     }
  ///
  /// NOTE: The context owns the memory referenced by partition_params_array. It
  /// will be cleared with another call to PreviewDelegatePartitioning, or after
  /// TfLiteDelegateParams::Prepare returns.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*PreviewDelegatePartitioning)(
      struct TfLiteContext* context, const TfLiteIntArray* nodes_to_replace,
      TfLiteDelegateParams** partition_params_array, int* num_partitions);

  /// Returns a TfLiteTensor struct for a given index.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  ///
  /// WARNING: This method may not be available on all platforms.
  TfLiteTensor* (*GetTensor)(const struct TfLiteContext* context,
                             int tensor_idx);

  /// Returns a TfLiteEvalTensor struct for a given index.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  ///
  /// WARNING: This method may not be available on all platforms.
  TfLiteEvalTensor* (*GetEvalTensor)(const struct TfLiteContext* context,
                                     int tensor_idx);

  /// Retrieves named metadata buffer from the TFLite model.
  /// Returns kTfLiteOk if metadata is successfully obtained from the flatbuffer
  /// Model: that is, there exists a `metadata` entry with given `name` string.
  /// (see TFLite's schema.fbs).
  /// The corresponding `buffer` information is populated in `ptr` & `bytes`.
  /// The data from `ptr` is valid for the lifetime of the Interpreter.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*GetModelMetadata)(const struct TfLiteContext* context,
                                   const char* name, const char** ptr,
                                   size_t* bytes);

  /// Retrieves the corresponding TfLiteContext of a subgraph that the given
  /// subgraph_index points to and switches to the delegate context for that
  /// subgraph. If an invalid subgraph index is given, returns kTfLiteError.
  ///
  /// NOTE: This function is expected to be paired with ReleaseSubgraphContext()
  /// once the delegate preparation is done and/or the delegate context
  /// functions are no longer needed.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*AcquireSubgraphContext)(
      struct TfLiteContext* context, int subgraph_index,
      struct TfLiteContext** acquired_context);
  /// Releases the subgraph context by switching back to the TFLite kernel
  /// context for the subgraph that the given subgraph_index points to.
  ///
  /// NOTE: This function is expected to be used after AcquireSubgraphContext()
  /// once the delegate preparation is done and/or the delegate context
  /// functions are no longer needed.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  TfLiteStatus (*ReleaseSubgraphContext)(struct TfLiteContext* context,
                                         int subgraph_index);
} TfLiteContext;

/// `TfLiteOperator` is an external version of `TfLiteRegistration`
/// for C API which doesn't use internal types (such as `TfLiteContext`) but
/// only uses stable API types (such as `TfLiteOpaqueContext`). The purpose of
/// each field is the exactly the same as with `TfLiteRegistration`.
typedef struct TfLiteOperator TfLiteOperator;

#ifndef DOXYGEN_SKIP
// For backwards compatibility.
// Deprecated. Use TfLiteOperator instead.
typedef TfLiteOperator TfLiteRegistrationExternal;
#endif

/// The valid values of the `inplace_operator` field in `TfLiteRegistration`.
/// This allow an op to signal to the runtime that the same data pointer
/// may be passed as an input and output without impacting the result.
/// This does not mean that the memory can safely be reused, it is up to the
/// runtime to determine this, e.g. if another op consumes the same input or not
/// or if an input tensor has sufficient memory allocated to store the output
/// data.
///
/// Setting these flags authorizes the runtime to set the data pointers of an
/// input and output tensor to the same value. In such cases, the memory
/// required by the output must be less than or equal to that required by the
/// shared input, never greater. If kTfLiteInplaceOpDataUnmodified is set, then
/// the runtime can share the same input tensor with multiple operator's
/// outputs, provided that kTfLiteInplaceOpDataUnmodified is set for all of
/// them. Otherwise, if an input tensor is consumed by multiple operators, it
/// may only be shared with the operator which is the last to consume it.
///
/// Note that this is a bitmask, so the values should be 1, 2, 4, 8, ...etc.
typedef enum {
  /// The default value. This indicates that the same data pointer cannot safely
  /// be passed as an op's input and output.
  kTfLiteInplaceOpNone = 0,
  /// This indicates that an op's first output's data is identical to its first
  /// input's data, for example Reshape.
  kTfLiteInplaceOpDataUnmodified = 1,
  /// Setting kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput means
  /// that InputN may be shared with OutputN instead of with the first output.
  /// This flag requires one or more of kTfLiteInplaceOpInputNShared to be set.
  kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput = 2,
  /// kTfLiteInplaceOpInputNShared indicates that it is safe for an op to share
  /// InputN's data pointer with an output tensor. If
  /// kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput is set then
  /// kTfLiteInplaceOpInputNShared indicates that InputN may be shared
  /// with OutputN, otherwise kTfLiteInplaceOpInputNShared indicates that InputN
  /// may be shared with the first output.
  ///
  /// Indicates that an op's first input may be shared with the first output
  /// tensor. kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput has
  /// no impact on the behavior allowed by this flag.
  kTfLiteInplaceOpInput0Shared = 4,
  /// Indicates that an op's second input may be shared with the first output
  /// if kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput is not set
  /// or second output if kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput
  /// is set.
  kTfLiteInplaceOpInput1Shared = 8,
  /// Indicates that an op's third input may be shared with the first output
  /// if kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput is not set
  /// or third output if kTfLiteInplaceInputCanBeSharedWithCorrespondingOutput
  /// is
  /// set.
  kTfLiteInplaceOpInput2Shared = 16,
  /// Placeholder to ensure that enum can hold 64 bit values to accommodate
  /// future fields.
  kTfLiteInplaceOpMaxValue = UINT64_MAX,
} TfLiteInPlaceOp;

/// The number of shareable inputs supported.
static const int kTfLiteMaxSharableOpInputs = 3;

/// `TfLiteRegistration` defines the implementation of an operation
/// (a built-in op, custom op, or custom delegate kernel).
///
/// It is a struct containing "methods" (C function pointers) that will be
/// invoked by the TF Lite runtime to evaluate instances of the operation.
///
/// See also `TfLiteOperator` which is a more ABI-stable equivalent.
typedef struct TfLiteRegistration {
  /// Initializes the op from serialized data.
  /// Called only *once* for the lifetime of the op, so any one-time allocations
  /// should be made here (unless they depend on tensor sizes).
  ///
  /// * If a built-in op:
  ///       * `buffer` is the op's params data (TfLiteLSTMParams*).
  ///       * `length` is zero.
  /// * If custom op:
  ///       * `buffer` is the op's `custom_options`.
  ///       * `length` is the size of the buffer.
  ///
  /// Returns a type-punned (i.e. void*) opaque data (e.g. a primitive pointer
  /// or an instance of a struct).
  ///
  /// The returned pointer will be stored with the node in the `user_data`
  /// field, accessible within prepare and invoke functions below.
  ///
  /// NOTE: if the data is already in the desired format, simply implement this
  /// function to return `nullptr` and implement the free function to be a
  /// no-op.
  void* (*init)(TfLiteContext* context, const char* buffer, size_t length);

  /// The pointer `buffer` is the data previously returned by an init
  /// invocation.
  void (*free)(TfLiteContext* context, void* buffer);

  /// prepare is called when the inputs this node depends on have been resized.
  /// `context->ResizeTensor()` can be called to request output tensors to be
  /// resized.
  /// Can be called multiple times for the lifetime of the op.
  ///
  /// Returns `kTfLiteOk` on success.
  TfLiteStatus (*prepare)(TfLiteContext* context, TfLiteNode* node);

  /// Execute the node (should read `node->inputs` and output to
  /// `node->outputs`).
  ///
  /// Returns `kTfLiteOk` on success.
  TfLiteStatus (*invoke)(TfLiteContext* context, TfLiteNode* node);

  /// `profiling_string` is called during summarization of profiling information
  /// in order to group executions together. Providing a value here will cause a
  /// given op to appear multiple times is the profiling report. This is
  /// particularly useful for custom ops that can perform significantly
  /// different calculations depending on their `user-data`.
  const char* (*profiling_string)(const TfLiteContext* context,
                                  const TfLiteNode* node);

  /// Builtin codes. If this kernel refers to a builtin this is the code
  /// of the builtin. This is so we can do marshaling to other frameworks like
  /// NN API.
  ///
  /// Note: It is the responsibility of the registration binder to set this
  /// properly.
  int32_t builtin_code;

  /// Custom op name. If the op is a builtin, this will be `null`.
  ///
  /// Note: It is the responsibility of the registration binder to set this
  /// properly.
  ///
  /// WARNING: This is an experimental interface that is subject to change.
  const char* custom_name;

  /// The version of the op.
  /// Note: It is the responsibility of the registration binder to set this
  /// properly.
  int version;

  /// The external (i.e. ABI-stable) version of `TfLiteRegistration`.
  /// Since we can't use internal types (such as `TfLiteContext`) for C API to
  /// maintain ABI stability.  C API user will provide `TfLiteOperator` to
  /// implement custom ops.  We keep it inside of `TfLiteRegistration` and use
  /// it to route callbacks properly.
  TfLiteOperator* registration_external;

  /// Retrieves asynchronous kernel.
  ///
  /// If the `async_kernel` field is nullptr, it means the operation described
  /// by this TfLiteRegistration object does not support asynchronous execution.
  /// Otherwise, the function that the field points to should only be called for
  /// delegate kernel nodes, i.e. `node` should be a delegate kernel node
  /// created by applying a delegate. If the function returns nullptr, that
  /// means that the underlying delegate does not support asynchronous execution
  /// for this `node`.
  struct TfLiteAsyncKernel* (*async_kernel)(TfLiteContext* context,
                                            TfLiteNode* node);

  /// Indicates if an operator's output may safely overwrite its inputs.
  /// See the comments in `TfLiteInPlaceOp`.
  uint64_t inplace_operator;
} TfLiteRegistration;

/// \private
/// Old version of `TfLiteRegistration` to maintain binary backward
/// compatibility.
/// The legacy registration type must be a POD struct type whose field types
/// must be a prefix of the field types in TfLiteRegistration, and offset of the
/// first field in TfLiteRegistration that is not present in the legacy
/// registration type must be greater than or equal to the size of the legacy
/// registration type.
///
/// WARNING: This structure is deprecated / not an official part of the
/// API. It should be only used for binary backward compatibility.
typedef struct TfLiteRegistration_V3 {
  void* (*init)(TfLiteContext* context, const char* buffer, size_t length);
  void (*free)(TfLiteContext* context, void* buffer);
  TfLiteStatus (*prepare)(TfLiteContext* context, TfLiteNode* node);
  TfLiteStatus (*invoke)(TfLiteContext* context, TfLiteNode* node);
  const char* (*profiling_string)(const TfLiteContext* context,
                                  const TfLiteNode* node);
  int32_t builtin_code;
  const char* custom_name;
  int version;
  TfLiteOperator* registration_external;
  struct TfLiteAsyncKernel* (*async_kernel)(TfLiteContext* context,
                                            TfLiteNode* node);
} TfLiteRegistration_V3;

/// \private
/// Old version of `TfLiteRegistration` to maintain binary backward
/// compatibility.
/// The legacy registration type must be a POD struct type whose field types
/// must be a prefix of the field types in TfLiteRegistration, and offset of the
/// first field in TfLiteRegistration that is not present in the legacy
/// registration type must be greater than or equal to the size of the legacy
/// registration type.
///
/// WARNING: This structure is deprecated / not an official part of the
/// API. It should be only used for binary backward compatibility.
typedef struct TfLiteRegistration_V2 {
  void* (*init)(TfLiteContext* context, const char* buffer, size_t length);
  void (*free)(TfLiteContext* context, void* buffer);
  TfLiteStatus (*prepare)(TfLiteContext* context, TfLiteNode* node);
  TfLiteStatus (*invoke)(TfLiteContext* context, TfLiteNode* node);
  const char* (*profiling_string)(const TfLiteContext* context,
                                  const TfLiteNode* node);
  int32_t builtin_code;
  const char* custom_name;
  int version;
  TfLiteOperator* registration_external;
} TfLiteRegistration_V2;

/// \private
/// Old version of `TfLiteRegistration` to maintain binary backward
/// compatibility.
/// The legacy registration type must be a POD struct type whose field types
/// must be a prefix of the field types in TfLiteRegistration, and offset of the
/// first field in TfLiteRegistration that is not present in the legacy
/// registration type must be greater than or equal to the size of the legacy
/// registration type.
///
/// WARNING: This structure is deprecated / not an official part of the
/// API. It should be only used for binary backward compatibility.
typedef struct TfLiteRegistration_V1 {
  void* (*init)(TfLiteContext* context, const char* buffer, size_t length);
  void (*free)(TfLiteContext* context, void* buffer);
  TfLiteStatus (*prepare)(TfLiteContext* context, TfLiteNode* node);
  TfLiteStatus (*invoke)(TfLiteContext* context, TfLiteNode* node);
  const char* (*profiling_string)(const TfLiteContext* context,
                                  const TfLiteNode* node);
  int32_t builtin_code;
  const char* custom_name;
  int version;
} TfLiteRegistration_V1;

/// The flags used in `TfLiteDelegate`. Note that this is a bitmask, so the
/// values should be 1, 2, 4, 8, ...etc.
typedef enum TfLiteDelegateFlags {
  kTfLiteDelegateFlagsNone = 0,
  /// The flag is set if the delegate can handle dynamic sized tensors.
  /// For example, the output shape of a `Resize` op with non-constant shape
  /// can only be inferred when the op is invoked.
  /// In this case, the Delegate is responsible for calling
  /// `SetTensorToDynamic` to mark the tensor as a dynamic tensor, and calling
  /// `ResizeTensor` when invoking the op.
  ///
  /// If the delegate isn't capable to handle dynamic tensors, this flag need
  /// to be set to false.
  kTfLiteDelegateFlagsAllowDynamicTensors = 1,

  /// This flag can be used by delegates (that allow dynamic tensors) to ensure
  /// applicable tensor shapes are automatically propagated in the case of
  /// tensor resizing. This means that non-dynamic (allocation_type !=
  /// kTfLiteDynamic) I/O tensors of a delegate kernel will have correct shapes
  /// before its Prepare() method is called. The runtime leverages TFLite
  /// builtin ops in the original execution plan to propagate shapes.
  ///
  /// A few points to note:
  /// 1. This requires kTfLiteDelegateFlagsAllowDynamicTensors. If that flag is
  /// false, this one is redundant since the delegate kernels are re-initialized
  /// every time tensors are resized.
  /// 2. Enabling this flag adds some overhead to AllocateTensors(), since extra
  /// work is required to prepare the original execution plan.
  /// 3. This flag requires that the original execution plan only have ops with
  /// valid registrations (and not 'dummy' custom ops like with Flex).
  ///
  /// WARNING: This feature is experimental and subject to change.
  kTfLiteDelegateFlagsRequirePropagatedShapes = 2,

  /// This flag can be used by delegates to request per-operator profiling. If a
  /// node is a delegate node, this flag will be checked before profiling. If
  /// set, then the node will not be profiled. The delegate will then add per
  /// operator information using `Profiler::EventType::OPERATOR_INVOKE_EVENT`
  /// and the results will appear in the operator-wise Profiling section and not
  /// in the Delegate internal section.
  kTfLiteDelegateFlagsPerOperatorProfiling = 4
} TfLiteDelegateFlags;

/// WARNING: This is an experimental interface that is subject to change.
typedef struct TfLiteDelegate {
  /// Data that delegate needs to identify itself. This data is owned by the
  /// delegate. The delegate is owned in the user code, so the delegate is
  /// responsible for deallocating this when it is destroyed.
  void* data_;

  /// Invoked by `ModifyGraphWithDelegate`. This prepare is called, giving the
  /// delegate a view of the current graph through `TfLiteContext*`. It
  /// typically will look at the nodes and call
  /// `ReplaceNodeSubsetsWithDelegateKernels()` to ask the TensorFlow lite
  /// runtime to create macro-nodes to represent delegated subgraphs of the
  /// original graph.
  TfLiteStatus (*Prepare)(TfLiteContext* context,
                          struct TfLiteDelegate* delegate);

  /// Copy the data from delegate buffer handle into raw memory of the given
  /// `tensor`. Note that the delegate is allowed to allocate the raw bytes as
  /// long as it follows the rules for `kTfLiteDynamic` tensors, in which case
  /// this cannot be null.
  TfLiteStatus (*CopyFromBufferHandle)(TfLiteContext* context,
                                       struct TfLiteDelegate* delegate,
                                       TfLiteBufferHandle buffer_handle,
                                       TfLiteTensor* tensor);

  /// Copy the data from raw memory of the given `tensor` to delegate buffer
  /// handle. This can be null if the delegate doesn't use its own buffer.
  TfLiteStatus (*CopyToBufferHandle)(TfLiteContext* context,
                                     struct TfLiteDelegate* delegate,
                                     TfLiteBufferHandle buffer_handle,
                                     TfLiteTensor* tensor);

  /// Free the Delegate Buffer Handle. Note: This only frees the handle, but
  /// this doesn't release the underlying resource (e.g. textures). The
  /// resources are either owned by application layer or the delegate.
  /// This can be null if the delegate doesn't use its own buffer.
  void (*FreeBufferHandle)(TfLiteContext* context,
                           struct TfLiteDelegate* delegate,
                           TfLiteBufferHandle* handle);

  /// Bitmask flags. See the comments in `TfLiteDelegateFlags`.
  int64_t flags;

  /// The opaque delegate builder associated with this object.  If set then the
  /// TF Lite runtime will give precedence to this field.  E.g. instead of
  /// invoking `Prepare` via the function pointer inside the `TfLiteDelegate`
  /// object, the runtime will first check if the corresponding function
  /// pointer inside `opaque_delegate_builder` is set and if so invoke that.
  ///
  /// If this field is non-null, then the `Prepare` field (of the
  /// `TfLiteDelegate`) should be null.
  struct TfLiteOpaqueDelegateBuilder* opaque_delegate_builder;
} TfLiteDelegate;

/// Build a `null` delegate, with all the fields properly set to their default
/// values.
TfLiteDelegate TfLiteDelegateCreate(void);

/// `TfLiteOpaqueDelegateBuilder` is used for constructing
/// `TfLiteOpaqueDelegate`, see `TfLiteOpaqueDelegateCreate` in c_api_opaque.h.
/// NOTE: This struct is not ABI stable.
///
/// For forward source compatibility `TfLiteOpaqueDelegateBuilder` objects
/// should be brace-initialized, so that all fields (including any that might be
/// added in the future) get zero-initialized.  The purpose of each field is
/// exactly the same as with `TfLiteDelegate`.
///
/// NOTE: This type is part of the TensorFlow Lite Extension APIs.
/// We reserve the right to make changes to this API in future releases,
/// potentially including non-backwards-compatible changes, on a different
/// schedule than for the other TensorFlow Lite APIs. See
/// https://www.tensorflow.org/guide/versions#separate_version_number_for_tensorflow_lite_extension_apis.
typedef struct TfLiteOpaqueDelegateBuilder {
  /// Data that delegate needs to identify itself. This data is owned by the
  /// delegate. The delegate is owned in the user code, so the delegate is
  /// responsible for deallocating this when it is destroyed.
  void* data;
  /// Invoked by ModifyGraphWithDelegate. This prepare is called, giving the
  /// delegate a view of the current graph through `TfLiteContext*`. It
  /// typically will look at the nodes and call
  /// `ReplaceNodeSubsetsWithDelegateKernels()` to ask the TensorFlow lite
  /// runtime to create macro-nodes to represent delegated subgraphs of the
  /// original graph.
  TfLiteStatus (*Prepare)(TfLiteOpaqueContext* context,  // NOLINT
                          TfLiteOpaqueDelegate* delegate, void* data);
  /// Copies the data from delegate buffer handle into raw memory of the given
  /// `tensor`. Note that the delegate is allowed to allocate the raw bytes as
  /// long as it follows the rules for kTfLiteDynamic tensors, in which case
  /// this cannot be null.
  TfLiteStatus (*CopyFromBufferHandle)(  // NOLINT
      TfLiteOpaqueContext* context, TfLiteOpaqueDelegate* delegate, void* data,
      TfLiteBufferHandle buffer_handle, TfLiteOpaqueTensor* tensor);
  /// Copies the data from raw memory of the given `tensor` to delegate buffer
  /// handle. This can be null if the delegate doesn't use its own buffer.
  TfLiteStatus (*CopyToBufferHandle)(  // NOLINT
      TfLiteOpaqueContext* context, TfLiteOpaqueDelegate* delegate, void* data,
      TfLiteBufferHandle buffer_handle, TfLiteOpaqueTensor* tensor);
  /// Frees the Delegate Buffer Handle. Note: This only frees the handle, but
  /// this doesn't release the underlying resource (e.g. textures). The
  /// resources are either owned by application layer or the delegate.
  /// This can be null if the delegate doesn't use its own buffer.
  void (*FreeBufferHandle)(TfLiteOpaqueContext* context,  // NOLINT
                           TfLiteOpaqueDelegate* delegate, void* data,
                           TfLiteBufferHandle* handle);
  /// Bitmask flags. See the comments in `TfLiteDelegateFlags`.
  int64_t flags;
} TfLiteOpaqueDelegateBuilder;

#ifndef TF_LITE_STATIC_MEMORY
// See c_api_opaque.h.
// This declaration in common.h is only for backwards compatibility.
// NOTE: This function is part of the TensorFlow Lite Extension APIs, see above.
TfLiteOpaqueDelegate* TfLiteOpaqueDelegateCreate(
    const TfLiteOpaqueDelegateBuilder* opaque_delegate_builder);

// See c_api_opaque.h.
// This declaration in common.h is only for backwards compatibility.
// NOTE: This function is part of the TensorFlow Lite Extension APIs, see above.
void TfLiteOpaqueDelegateDelete(TfLiteOpaqueDelegate* delegate);
#endif  // TF_LITE_STATIC_MEMORY

// See c_api_opaque.h.
// This declaration in common.h is only for backwards compatibility.
// NOTE: This function is part of the TensorFlow Lite Extension APIs, see above.
void* TfLiteOpaqueDelegateGetData(const TfLiteOpaqueDelegate* delegate);

/// Returns a tensor data allocation strategy.
TfLiteAllocationStrategy TfLiteTensorGetAllocationStrategy(
    const TfLiteTensor* t);

/// Returns how stable a tensor data buffer address is across runs.
TfLiteRunStability TfLiteTensorGetBufferAddressStability(const TfLiteTensor* t);

/// Returns how stable a tensor data values are across runs.
TfLiteRunStability TfLiteTensorGetDataStability(const TfLiteTensor* t);

/// Returns the operation step when the data of a tensor is populated.
///
/// Some operations can precompute their results before the evaluation step.
/// This makes the data available earlier for subsequent operations.
TfLiteRunStep TfLiteTensorGetDataKnownStep(const TfLiteTensor* t);

/// Returns the operation steop when the shape of a tensor is computed.
///
/// Some operations can precompute the shape of their results before the
/// evaluation step. This makes the shape available earlier for subsequent
/// operations.
TfLiteRunStep TfLiteTensorGetShapeKnownStep(const TfLiteTensor* t);

/** @} */
// Ends `\addtogroup`, it's important for the doc generator that this doesn't
// include the CC code below.

#ifdef __cplusplus
}  // extern "C"

#include <utility>

// --- TFLITE VARIANT TENSORS ----
// Programming languges usually define "variant" as a type that can hold an
// unbounded set of types. See std::any
// (https://en.cppreference.com/w/cpp/utility/any) for a related standard
// library construct. In tensorflow, variant tensors have a data member which is
// an Object that is destructible and copy constructible.
//   Variant tensors are commonly used to represent non trivial data
// semantics that don't fit into simple primitives, such as lists of tensors and
// datasets. Additionally, they can facilitate containers for optimizing
// memory movement of tensor data.
//
// The following set of classes define the variant tensor member for tflite.
// They implement a type-erased container intended to be used behind the
// `data.data : void*` member of `TfLiteTensor`s. Runtime functions interact
// the variant member at the level of a `VariantData`, whereas kernels
// operate with the full knowledge of the un-erased type. The `VariantData`
// class provides abstract methods for destroying and copying `VariantData`.
// Invoking these methods will dispatch to the erased type opaquely.
//    The contents of any object of type derived from `AbstractVariant` can be
// written to `TfLiteTensor::data::data : void*` from kernels. If the runtime
// were to copy such a tensor through `TfLiteTensorCopy`, the destination data
// member will contain the result of invoking the erased type's copy
// constructor. Similar for the runtime releasing tensors from memory, the
// erased type's destructor will be invoked. There are a few caveats to consider
// to use these safely, which we discuss below.
//
// EXAMPLE: READING VARIANT TENSORS
//   ```
//   // retrieve input with `type == kTfLiteVariant`
//   TfLiteTensor* input = ...
//   // must first static cast to `VariantData`, more on this below.
//   VariantData* vd_input = static_cast<VariantData*>(t->data.data);
//   CustomType* typed_input =
//   static_cast<CustomType*>(vd_input);
//   // do custom work on `typed_input`...
//   ```
//
// EXAMPLE: WRITING VARIANT TENSORS
//   ```
//   TfLiteTensor* output = ...
//   // construct a new variant object behind the target tensor
//   TfLiteVariantRealloc<DerivedType, DerivedArgs...>(output, args...);
//   // again must static cast to `VariantData*` before writing to `void*`.
//   output->data.data = static_cast<VariantData*>(typed_output);
//   ```
//
// WHY STATIC CAST TO `VariantData*`
//    The Standard defines a `reinterpret_cast` from a derived type to its
// parents as undefined behavior when the parent is a non-standard layout.
// https://en.cppreference.com/w/cpp/language/reinterpret_cast (see bullet 5).
// Due to the `VariantData` having virtual members it is indeed non-standard
// layout, and any type derived from `VariantData` fails to be
// "transparently-replaceable". I.e. implicit cast from derived to base in this
// case may adjust the pointer and by definition `reinterpret_cast` will not
// the adjust the pointer.
//    Thus, dereferencing a pointer of type `VariantData` which addresses
// the first byte of an object of said derived type is UB unless it was first
// implicitly or statically casted to a `VariantData`. Writing the object of
// derived type directly to `void*` which is dereferenced as a `VariantData` is
// then UB, and so the intermediate cast through `VariantData` must be enforced.
//    A good example of this issue is ellucidate in the bottom code snippet
// here: https://en.cppreference.com/w/cpp/utility/launder.
class VariantData {
 public:
  // All variant objects must be able to be destroyed and copied.
  virtual ~VariantData() = default;
  // A "virtual copy-constructor". Often the destination tensor of a variant
  // copy may have been previously allocated in a prior call to inference. We
  // allow the copy to target the destinations buffer (`maybe_alloc`),
  // for potential reuse and optimizations. `maybe_alloc` must be of the same
  // underlying derived type. References to whatever object is at
  // `maybe_alloc` may be invalidated.
  virtual VariantData* CloneTo(VariantData* maybe_alloc) const = 0;
};

// Concrete implementations extend `AbstractVariantData` with CRPT.
template <typename ErasedDerived>
class AbstractVariantData : public VariantData {
 public:
  VariantData* CloneTo(VariantData* maybe_alloc) const override {
    if (maybe_alloc != nullptr) {
      // If the output is still allocated, then its object may still be
      // in its life time and the destructor must be called before re-using the
      // buffer.
      //     This may actual have a non-negligible effect on performance if the
      // destructor is complex. A future iteration may
      // introduce copy or move assignment semantics, allowing for the
      // underlying implementation to optimize for this case.
      auto* derived = static_cast<ErasedDerived*>(maybe_alloc);
      derived->~ErasedDerived();
      return new (derived)
          ErasedDerived(static_cast<ErasedDerived const&>(*this));
    }
    return new ErasedDerived(static_cast<ErasedDerived const&>(*this));
  }

 protected:
  AbstractVariantData() = default;
  AbstractVariantData(const AbstractVariantData&) = default;
  AbstractVariantData(AbstractVariantData&&) = delete;
};

// Analogous to `TfLiteTensorRealloc` for allocation of tensors whose
// data member points to an arbitrary C++ object. `VariantType` refers
// to the erased type of said object and `VariantArgs` refers to
// a list of argument types with which to construct a new `VariantType`.
// `VariantArgs` must match a constructor of `VariantType`.
template <class VariantType, class... VariantArgs>
TfLiteStatus TfLiteTensorVariantRealloc(TfLiteTensor* t,
                                        VariantArgs&&... args) {
  if (t->type != kTfLiteVariant) return kTfLiteError;
  VariantType* new_vd;
  if (t->data.raw != nullptr) {
    auto* target_vd = static_cast<VariantData*>(t->data.data);
    target_vd->~VariantData();
    // As above, we assume if `t` is already allocated then it was allocated
    // with the same `VariantType` as templated.
    new_vd = new (t->data.raw) VariantType(std::forward<VariantArgs>(args)...);
  } else {
    new_vd = new VariantType(std::forward<VariantArgs>(args)...);
  }
  t->data.data = static_cast<VariantData*>(new_vd);
  t->allocation_type = kTfLiteVariantObject;
  return kTfLiteOk;
}

#endif  // __cplusplus
#endif  // TENSORFLOW_LITE_CORE_C_COMMON_H_
