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//
// Copyright © 2017 Arm Ltd. All rights reserved.
// SPDX-License-Identifier: MIT
//
#include "Softmax.hpp"
#include <cmath>
#include <vector>
namespace armnn
{
unsigned int GetNumElementsBetween(const TensorShape& shape,
unsigned int firstAxisInclusive,
unsigned int lastAxisExclusive)
{
BOOST_ASSERT(0 <= firstAxisInclusive);
BOOST_ASSERT(firstAxisInclusive <= lastAxisExclusive);
BOOST_ASSERT(lastAxisExclusive <= shape.GetNumDimensions());
unsigned int count = 1;
for (unsigned int i = firstAxisInclusive; i < lastAxisExclusive; i++)
{
count *= shape[i];
}
return count;
}
/// Computes the softmax function on some inputs, into outputs, with a shape given by tensorInfo.
void Softmax(Decoder<float>& in, Encoder<float>& out, const TensorInfo& inputTensorInfo, float beta, int axis)
{
BOOST_ASSERT_MSG(axis < static_cast<int>(inputTensorInfo.GetNumDimensions()),
"Required axis index greater than number of dimensions.");
BOOST_ASSERT_MSG(axis >= -static_cast<int>(inputTensorInfo.GetNumDimensions()),
"Required axis index lower than negative of the number of dimensions");
unsigned int uAxis = axis < 0 ?
inputTensorInfo.GetNumDimensions() - static_cast<unsigned int>(abs(axis))
: static_cast<unsigned int>(axis);
const TensorShape& inputShape = inputTensorInfo.GetShape();
const unsigned int outerSize = GetNumElementsBetween(inputShape, 0, uAxis);
const unsigned int axisSize = inputShape[uAxis];
const unsigned int innerSize = GetNumElementsBetween(inputShape, uAxis + 1, inputShape.GetNumDimensions());
for (unsigned int outer = 0; outer < outerSize; ++outer)
{
unsigned int inputBeginIdx = outer * axisSize * innerSize;
unsigned int inputEndIdx = inputBeginIdx + axisSize * innerSize;
unsigned int outputBeginIdx = outer * axisSize * innerSize;
for (unsigned int inner = 0; inner < innerSize; ++inner, ++inputBeginIdx, ++inputEndIdx, ++outputBeginIdx)
{
// Find max
float maxValue = std::numeric_limits<float>::lowest();
for (unsigned int iter = inputBeginIdx; iter < inputEndIdx; iter += innerSize)
{
in[iter];
maxValue = std::max(maxValue, in.Get());
}
// Compute sum
float sum = 0.0f;
for (unsigned int iter = inputBeginIdx; iter < inputEndIdx; iter += innerSize)
{
in[iter];
sum += std::exp((in.Get() - maxValue) * beta);
}
// Compute result
unsigned int outputIter = outputBeginIdx;
out[outputIter];
for (unsigned int iter = inputBeginIdx; iter < inputEndIdx; iter += innerSize, outputIter += innerSize)
{
out[outputIter];
in[iter];
out.Set(std::exp((in.Get() - maxValue) * beta) / sum);
}
}
}
}
} //namespace armnn
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