G4Pow.cc

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//
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4Pow
//
// Author:        Vladimir Ivanchenko
//
// Creation date: 23.05.2009
//
// Modifications:
// 08.01.2011 V.Ivanchenko extended maxZ from 256 to 512
// 02.05.2013 V.Ivanchenko added expA and logX methods,
//            revised A13, logA, powZ, powA to improved accuracy
// 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 = 0;

// -------------------------------------------------------------------

G4Pow* G4Pow::GetInstance()
{
  if (fpInstance == 0)
  {
    static G4Pow geant4pow;
    fpInstance = &geant4pow;
  }
  return fpInstance;
}

// -------------------------------------------------------------------

G4Pow::G4Pow()
  : onethird(1.0/3.0), max2(5)
{
#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);
  }

}

// -------------------------------------------------------------------

G4Pow::~G4Pow()
{}

// -------------------------------------------------------------------

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 bool 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;
}