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 * distributed with this work for additional information
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 * to you 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.
 */

/*!
 * \file src/relay/qnn/op/dequantize.cc
 * \brief QNN dequantize operator. Dequantize operator converts from quantized
 * domain to unquantized domain.
 */

#include <tvm/relay/analysis.h>
#include <tvm/relay/op_attr_types.h>
#include <tvm/relay/qnn/attrs.h>
#include "../../transforms/pattern_util.h"
#include "../util.h"

namespace tvm {
namespace relay {
namespace qnn {

bool DequantizeRel(const Array<Type>& types,
                   int num_inputs,
                   const Attrs& attrs,
                   const TypeReporter& reporter) {
  CHECK_EQ(types.size(), 4);
  const auto* data = types[0].as<TensorTypeNode>();
  CHECK(data != nullptr);
  const auto input_dtype = data->dtype;
  CHECK(input_dtype == DataType::Int(8) ||
        input_dtype == DataType::UInt(8) ||
        input_dtype == DataType::Int(32))
    << "Input type should be one of the quantized types [unit8, int8, int32] but was "
    <<  input_dtype;

  // Check the types of scale and zero points.
  CHECK(IsScalarType(types[1], DataType::Float(32)));  // input_scale
  CHECK(IsScalarType(types[2], DataType::Int(32)));    // input_zero_point

  const Array<tvm::PrimExpr> oshape = data->shape;
  // assign output type, output will always be float 32.
  reporter->Assign(types[3], TensorType(oshape, DataType::Float(32)));
  return true;
}

Expr MakeDequantize(Expr data, Expr input_scale, Expr input_zero_point) {
  // real_value = scale * (quantized_value - zero_point)
  // A more detailed explanation can be found here -
  // https://github.com/google/gemmlowp/blob/master/doc/quantization.md
  static const Op& op = Op::Get("qnn.dequantize");
  return Call(op, {data, input_scale, input_zero_point}, Attrs(), {});
}

Expr DequantizeLower(const Expr& input_tensor, const Expr& input_scale,
                     const Expr& input_zero_point) {
  auto shift = Subtract(Cast(input_tensor, DataType::Int(32)), input_zero_point);
  auto scaled_output = Multiply(Cast(shift, DataType::Float(32)), input_scale);
  return scaled_output;
}

Expr DequantizeQnnCanonicalize(const Attrs& attrs, const Array<Expr>& new_args,
                               const Array<tvm::relay::Type>& types) {
  CHECK_EQ(new_args.size(), 3);
  auto& data = new_args[0];
  auto& input_scale = new_args[1];
  auto& input_zero_point = new_args[2];
  CHECK_EQ(types.size(), 4);
  return DequantizeLower(data, input_scale, input_zero_point);
}

RELAY_REGISTER_OP("qnn.dequantize")
.describe(R"code(Dequantizes the input and produces float32 output.
The input is always quantized (int8, uint8) and will be converted to float32 given input scale and zero_point.
- **data**: Quantized tensor of any shape to dequantize. The input data can be of floating point
)code" TVM_ADD_FILELINE)
.set_num_inputs(3)
.add_argument("data", "Tensor", "The tensor to dequantize.")
.add_argument("input_scale", "Tensor", "The quantization scale of the input tensor.")
.add_argument("input_zero_point", "Tensor", "The quantization zero_point of the input tensor.")
.set_support_level(11)
.add_type_rel("Dequantize", DequantizeRel)
.set_attr<FTVMLegalize>("FTVMQnnCanonicalize", DequantizeQnnCanonicalize);

TVM_REGISTER_GLOBAL("relay.qnn.op._make.dequantize")
.set_body_typed(MakeDequantize);

}  // namespace qnn
}  // namespace relay
}  // namespace tvm
