Conversion table class for 10-8bit compression.

[u/mrichter/AliRoot.git] / HLT / misc / AliTransBit.cxx

///////////////////////////////////////////////////////////////////////////////
//                                                                           //
//  Time Projection Chamber ADC bit compresion lookup table                  //
//                                                                           // 
//
//  Origin: Marian Ivanov , GSI Darmstadt                                   // 
//                                                                          //

//  
/*
  Conversion equation:  
  For AliTransBit_v1   
  dy/dx= Int_t(1+x/fX0)

  For AliTransBit_v2    
  y  =(2**bit0) ln(1+x/fX0) / ln(1+(2**bit1-1)/fX0)                        
  
  where x0 is calculated in function GetOptimumX0()
    
*/

// Example Session                                                          // 
/*

Int_t b0=10;  // original number of bits
  Int_t b1=8;   // compressed

  AliTransBit_v1 trans;
  Int_t x0=TMath::Nint(TMath::Exp(b0*TMath::Log(2)));
  Int_t x1=TMath::Nint(TMath::Exp(b1*TMath::Log(2)));  
  trans.SetBits(b0,b1);
  trans.FindOptimumX0();
  trans.Update();
  cout<<trans.Get0to1(x0-2)<<"\n";
  cout<<trans.Get1to0(x1-2)<<"\n";
   
  // to produce table of 
  for( Int_t i=0;i<x1;i++) cout<<i<<"\t"<<trans.Get1to0(i)<<"\n"; > table1to0.txt
  for( Int_t i=0;i<x0;i++) cout<<i<<"\t"<<trans.Get0to1(i)<<"\n"; > table0to1.txt

  for( Int_t i=0;i<x1-1;i++) cout<<i<<"\t"<<trans.Get1to0(i+1)-trans.Get1to0(i)<<"\n"; > tabled.txt

  

*/
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/*                                                                          // 
<img src="gif/AliTPCTransBit.gif">  
*/
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//                                                                          //
///////////////////////////////////////////////////////////////////////////////


#include "AliTransBit.h"
#include "TMath.h"
#include "iostream.h"

ClassImp(AliTransBit)
ClassImp(AliTransBit_v1)
ClassImp(AliTransBit_v2)


AliTransBit::AliTransBit()
{
  //
  //
  fTable0 = 0;
  fTable1 = 0;
  fBit0   = 10;
  fBit1   = 8;
  fX0     = 0;
}

AliTransBit::~AliTransBit() 
{
  //
  //default destructor
  if (fTable0!=0) delete [] fTable0;
  if (fTable1!=0) delete [] fTable1;
}





Double_t AliTransBit_v1::FindOptimumX0()
{
  //
  //find x0 for which derivation at xder1 is equal 1
  //
  Int_t x0=TMath::Nint(TMath::Exp(fBit0*TMath::Log(2)));
  Int_t x1=TMath::Nint(TMath::Exp(fBit1*TMath::Log(2)));

  fX0 = ((x1-2)*(x1-2)/2.)/(x0-x1-1);  //starting fX0
  Int_t digit=0;
  Int_t j;
  Double_t weight=1;
  for(j=0;(j<50)&&(digit!=(x0-1));j++){  
    Int_t olddigit=digit;
    digit=0;
    for (Int_t  i=0; i<x1-1;i++) digit+= Int_t(1+Double_t(i)/fX0);      
    fX0*= (1.+weight*Double_t(digit)/Double_t(x0-1))/(1.+weight);    
    if ( ((olddigit-(x0-1)) * (digit-(x0-1))) <0 ) 
      weight*=0.25;
    // cout<<j<<"\t"<<fX0<<"\t"<<digit<<"\n";
  }
  //  cout<<"End of iteration "<<j<<"\n";
  //cout<<"digit..."<<digit<<"\n";  
  return fX0;
}


void AliTransBit_v1::Update()
{
  //
  //construct lookup tables for loosy compresion from 
  if (fX0<1) fX0 = FindOptimumX0();  
  Int_t x0=TMath::Nint(TMath::Exp(fBit0*TMath::Log(2)));
  Int_t x1=TMath::Nint(TMath::Exp(fBit1*TMath::Log(2)));
  
  //fTable0 - conversion from bit0 coding to bit1 coding
  if (fTable0!=0) delete fTable0;
  fTable0= new Int_t[x0];
  //fTable1 - conversion table from bit1 to bit0 coding
  if (fTable1!=0) delete [] fTable1;
  fTable1= new Int_t[x1];
  //   
  Int_t digit=0;
  for (Int_t  i=0; i<x1-1;i++){    
    Int_t ddig=Int_t(1+Double_t(i)/fX0);
    for (Int_t j=0;j<ddig;j++) if ((digit+j)<x0) fTable0[digit+j] = i;    
    fTable1[i]= digit+ddig/2;
    digit+= ddig;
  } 
  for (Int_t i=digit;i<x0-1;i++) fTable0[i]=x1-2;
  fTable1[x1-1]=x0-1; //overflow 
  fTable0[x0-1]=x1-1; //overflow    
  return;
}


Double_t AliTransBit_v2::FindOptimumX0()
{
  //
  //find x0 for which derivation at xder1 is equal 1
  //
  const Float_t xder1=1;
  const Float_t dx=0.1;

  Float_t x0=TMath::Exp(fBit0*TMath::Log(2));
  Float_t x1=TMath::Exp(fBit1*TMath::Log(2));
  Float_t deriv = 0;
  Float_t x;
  for (x=x1;( (x>1)&&(deriv<1)) ;x-=dx)
    {
      deriv = (x1-1)/( TMath::Log(1.+x0/x) *x *(1+xder1/x));
    }
  x+=dx/2.;
  fX0 = x;
  return fX0;
}


void AliTransBit_v2::Update()
{
  //
  //construct lookup tables for loosy compresion from 
  if (fX0<1) fX0 = FindOptimumX0();  
  //Float_t x0=TMath::Nint(TMath::Exp(fBit0*TMath::Log(2)));
  //Float_t x1=TMath::Nint(TMath::Exp(fBit1*TMath::Log(2)));
  Int_t x0=TMath::Nint(TMath::Exp(fBit0*TMath::Log(2)));
  Int_t x1=TMath::Nint(TMath::Exp(fBit1*TMath::Log(2)));
  
  //fTable0 - conversion from bit0 coding to bit1 coding
  if (fTable0!=0) delete fTable0;
  fTable0= new Int_t[x0];

  //fTable1 - conversion table from bit1 to bit0 coding
  if (fTable1!=0) delete [] fTable1;
  fTable1= new Int_t[x1];

  //  
  Int_t i;

  for ( i=0; i<x0;i++)
      fTable0[i] =TMath::Nint((x1-0.501)*TMath::Log(1.+Float_t(i)/fX0)/
				 TMath::Log(1.+(x0-1)/fX0));

  Int_t old0=-1;
  Int_t old1=-1;
  Int_t new1;
  for ( i=0; i<x0;i++){
      new1 = fTable0[i];
      if (new1!=old1){
	if (old1>=0) fTable1[old1] =(old0+i)/2;
	old0 = i;
	old1 = new1;
      }
  }
  fTable1[old1]=TMath::Nint((Float_t)(old0+x0)/2);
  
  return;
}