approx_erf.h

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#ifndef APPROX_ERF_H
#define APPROX_ERF_H
#include "DataFormats/Math/interface/approx_exp.h"

constexpr float approx_erf(float x) {
  auto xx = std::min(std::abs(x), 5.f);
  xx *= xx;
  return std::copysign(std::sqrt(1.f - unsafe_expf<4>(-xx * (1.f + 0.2733f / (1.f + 0.147f * xx)))), x);
  // return std::sqrt(1.f- std::exp(-x*x*(1.f+0.2733f/(1.f+0.147f*x*x)) ));
}

#endif