softmax_shared.cc

#include "caffe2/core/context.h"
#include "caffe2/core/operator.h"
#include "caffe2/utils/math.h"

namespace caffe2 {

void SoftmaxCPU(
    CPUContext& context,
    const int N,
    const int D,
    const float* Xdata,
    float* Ydata,
    float* scale,
    const float* sum_multiplier,
    bool logarithmic,
    float* rowmax) {
  math::RowwiseMax<float, CPUContext>(N, D, Xdata, rowmax, &context);
  // Put the intermediate result X - max(X) into Y
  context.template CopyFromCPU<float>(N * D, Xdata, Ydata);
  // Subtract the max (for numerical reasons)
  math::Gemm<float, CPUContext>(
      CblasNoTrans,
      CblasNoTrans,
      N,
      D,
      1,
      -1,
      rowmax,
      sum_multiplier,
      1,
      Ydata,
      &context);
  // Exponentiation
  math::Exp<float, CPUContext>(N * D, Ydata, Ydata, &context);
  math::Gemv<float, CPUContext>(
      CblasNoTrans, N, D, 1, Ydata, sum_multiplier, 0, scale, &context);
  // Do division
  // TODO(Yangqing): maybe implement it more beautifully?
  if (!logarithmic) {
    for (int i = 0; i < N; ++i) {
      for (int j = 0; j < D; ++j) {
        Ydata[i * D + j] /= scale[i];
      }
    }
  } else {
    for (int i = 0; i < N; ++i) {
      for (int j = 0; j < D; ++j) {
        Ydata[i * D + j] =
            Xdata[i * D + j] - rowmax[i] - log(fmaxf(scale[i], 1e-20f));
      }
    }
  }
}

} // namespace caffe2