G4Pow.cc

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//
// $Id$
//
// -------------------------------------------------------------------
//
// 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
//
// -------------------------------------------------------------------
 
#include "G4Pow.hh"
 
G4Pow* G4Pow::fInstance = 0;
 
// -------------------------------------------------------------------
 
G4Pow* G4Pow::GetInstance()
{
  if (fInstance == 0)
  {
    static G4Pow manager;
    fInstance = &manager;
  }
  return fInstance;
}
 
// -------------------------------------------------------------------
 
G4Pow::G4Pow()
{
  const G4int maxZ = 512; 
  const G4int maxZfact = 170; 
 
  pz13.resize(maxZ,0.0);
  lz.resize(maxZ,0.0);
  fact.resize(maxZfact,0.0);
  logfact.resize(maxZ,0.0);
 
  onethird = 1.0/3.0;
  G4double f = 1.0;
  G4double logf = 0.0;
  fact[0] = 1.0;
 
  for(G4int i=1; i<maxZ; ++i)
  {
    G4double x  = G4double(i);
    pz13[i] = std::pow(x,onethird);
    lz[i]   = std::log(x);
    if(i < maxZfact) { 
      f *= x; 
      fact[i] = f;
    }
    logf += lz[i];
    logfact[i] = logf;
  }
}
 
// -------------------------------------------------------------------
 
G4Pow::~G4Pow()
{}
 
// -------------------------------------------------------------------
 
G4double G4Pow::powN(G4double x, G4int n)
{
  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) && (x != 0.0))
  {
    G4double y = 1.0/x;
    G4int nn = -n;
    for(G4int i=0; i<nn; ++i) { res *= y; }
  }
  return res;
}