G4Pow.cc

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//
// G4Pow class implemenation
//
// Author: Vladimir Ivanchenko, 23.05.2009
// Revisions:
// - 23.03.2018, M.Novak: increased accuracy of A13 on the most critical
//                        [1/4,4] interval by introducing a denser(0.25) grid
// --------------------------------------------------------------------
 
#include "G4Pow.hh"
#include "G4Threading.hh"
 
G4Pow* G4Pow::fpInstance = nullptr;
 
// -------------------------------------------------------------------
 
G4Pow* G4Pow::GetInstance()
{
  if(fpInstance == nullptr)
  {
    static G4Pow geant4pow;
    fpInstance = &geant4pow;
  }
  return fpInstance;
}
 
// -------------------------------------------------------------------
 
G4Pow::G4Pow()
{
#ifdef G4MULTITHREADED
  if(G4Threading::IsWorkerThread())
  {
    G4Exception("G4Pow::G4Pow()", "InvalidSetup", FatalException,
                "Attempt to instantiate G4Pow in worker thread!");
  }
#endif
  const G4int maxZ     = 512;
  const G4int maxZfact = 170;
  const G4int numLowA  = 17;
 
  maxA    = -0.6 + maxZ;
  maxLowA = 4.0;
  maxA2   = 1.25 + max2 * 0.2;
  maxAexp = -0.76 + maxZfact * 0.5;
 
  ener.resize(max2 + 1, 1.0);
  logen.resize(max2 + 1, 0.0);
  lz2.resize(max2 + 1, 0.0);
  pz13.resize(maxZ, 0.0);
  lowa13.resize(numLowA, 0.0);
  lz.resize(maxZ, 0.0);
  fexp.resize(maxZfact, 0.0);
  fact.resize(maxZfact, 0.0);
  logfact.resize(maxZ, 0.0);
 
  G4double f    = 1.0;
  G4double logf = 0.0;
  fact[0]       = 1.0;
  fexp[0]       = 1.0;
 
  for(G4int i = 1; i <= max2; ++i)
  {
    ener[i]  = powN(500., i);
    logen[i] = G4Log(ener[i]);
    lz2[i]   = G4Log(1.0 + i * 0.2);
  }
 
  for(G4int i = 1; i < maxZ; ++i)
  {
    G4double x = G4double(i);
    pz13[i]    = std::pow(x, onethird);
    lz[i]      = G4Log(x);
    if(i < maxZfact)
    {
      f *= x;
      fact[i] = f;
      fexp[i] = G4Exp(0.5 * i);
    }
    logf += lz[i];
    logfact[i] = logf;
  }
 
  for(G4int i = 4; i < numLowA; ++i)
  {
    lowa13[i] = std::pow(0.25 * i, onethird);
  }
}
 
// -------------------------------------------------------------------
 
G4double G4Pow::A13(G4double A) const
{
  G4double res = 0.;
  if(A > 0.)
  {
    const bool invert = (A < 1.);
    const G4double a  = invert ? 1. / A : A;
    res               = (a < maxLowA) ? A13Low(a, invert) : A13High(a, invert);
  }
  return res;
}
 
// -------------------------------------------------------------------
 
G4double G4Pow::A13High(const G4double a, const bool invert) const
{
  G4double res;
  if(a < maxA)
  {
    const G4int i    = static_cast<G4int>(a + 0.5);
    const G4double x = (a / i - 1.) * onethird;
    res              = pz13[i] * (1. + x - x * x * (1. - 1.666667 * x));
  }
  else
  {
    res = G4Exp(G4Log(a) * onethird);
  }
  res = invert ? 1. / res : res;
  return res;
}
 
// -------------------------------------------------------------------
 
G4double G4Pow::A13Low(const G4double a, const G4bool invert) const
{
  G4double res;
  const G4int i    = static_cast<G4int>(4. * (a + 0.125));
  const G4double y = 0.25 * i;
  const G4double x = (a / y - 1.) * onethird;
  res              = lowa13[i] * (1. + x - x * x * (1. - 1.666667 * x));
  res              = invert ? 1. / res : res;
  return res;
}
 
// -------------------------------------------------------------------
 
G4double G4Pow::powN(G4double x, G4int n) const
{
  if(0.0 == x)
  {
    return 0.0;
  }
  if(std::abs(n) > 8)
  {
    return std::pow(x, G4double(n));
  }
  G4double res = 1.0;
  if(n >= 0)
  {
    for(G4int i = 0; i < n; ++i)
    {
      res *= x;
    }
  }
  else if(n < 0)
  {
    G4double y = 1.0 / x;
    G4int nn   = -n;
    for(G4int i = 0; i < nn; ++i)
    {
      res *= y;
    }
  }
  return res;
}