Fast_Exponential.h

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// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#pragma once
 
namespace Mantid {
namespace Kernel {
 
#define EXP_A (1048576 / M_LN2)
#define EXP_C 60801
 
inline double fast_exp(double y) {
  static union {
    double d;
#ifdef LITTLE_ENDIAN
    struct {
      int j, i;
    } n;
#else
    struct {
      int i, j;
    } n;
#endif
  } _eco;
 
  _eco.n.i = (int)(EXP_A * (y)) + (1072693248 - EXP_C);
  _eco.n.j = 0;
 
  return _eco.d;
}
 
} // Namespace Kernel
} // Namespace Mantid