1. Alberto Fassò Endre Futó
FLUKA in ROOT
Alberto Fassò
Endre Futó

2. Introduction FLUKA is written in FORTRAN77 (~900 routines)
It is excluded to rewrite it in C++
Present use of FLUKA:
- FORTRAN user routines having access to the information in the COMMONs
Solution:
- Rewrite COMMONs to C++ header files
- Rewrite only user routines to C++
(better: call from FORTRAN user routines
corresponding C++ procedures)

3. Main differences between FORTRAN and C++ (1)
Arrays:
FORTRAN: columnwise (leftmost subscripts vary fastest)
C++: rowwise (rightmost subscipts vary fastest)
Subroutine arguments:
FORTRAN: to be passed by reference
C++: non-array arguments passed by value, therefore declare them to be passed by ref or const ref
C++: array args are declared arrays, but actually passed by ref, because C++ converts use of array name to a pointer to the array's first element
C++: args not modified by FORTRAN to be declared const

4. Main differences between FORTRAN and C++ (2)
Be aware of storing vars in memory
LOGICAL variables
exponent should be e (not d)
If in C++ number starts with 0 -> octal number
Character variables (no string in FORTRAN)
No blanks in C++ variable names
Problem of EQUIVALENCE -> union
Input/Ouput: avoid doing input or output from both languages with the same file or device
There may be implementation-specific behaviours, but generally the output of the two will be intermingled

5. Rewrite COMMONs to C++ header files
Perl script c2h.pl far from being perfect, question of time and effort to write a better one, therefore always check:
Multidimensional arrays (swap dimensions)
Arrays dimensioned X(n:m) -> X[n-m+1]
CHARACTER* vars -> swap dim and char size
LOGICAL vars -> all should be integers
All comment lines
All continuation lines
All unions created from EQUIVALENCEs
All double constants -> exponent should be e
All exp constants -> exp cannot start with 0

6. Rewrite COMMONs to C++ header files
extern “C” {
typedef struct { Double_t whasou[12]; Double_t tkesum; Int_t lussrc; } episorCommon;
#define EPISOR COMMON_BLOCK(EPISOR,episor) COMMON_BLOCK_DEF(episorCommon, EPISOR);
typedef struct { Char_t sdsou[8]; } chepsrCommon;
#define CHEPSR COMMON_BLOCK(CHEPSR,chepsr) COMMON_BLOCK_DEF(chepsrCommon, CHEPSR); }
* /EPISOR/
LOGICAL LUSSRC
CHARACTER SDUSOU*8
COMMON /EPISOR/ WHASOU(12),TKESUM,LUSSRC
COMMON /CHEPSR/ SDUSOU

7. Mixing FORTRAN and C++ header.h
#ifndef __CFORTRAN_LOADED #include “....../root/include/cfortran.h” #endif #ifndef WIN32
#ifndef WIN32 #define flukam flukam_ #else #define flukam FLUKAM #endif
extern “C” { void flukam (const int& iflgeo); // COMMON /AAAAAA/ AA, BB, II, JJ typedef {double aa; double bb; int ii; int jj;} aaaaaaCommon; #define AAAAAA COMMON_BLOCK(AAAAAA,aaaaaa) COMMON_BLOCK_DEF(aaaaaaCommon,AAAAAA); }

8. Mixing FORTRAN and C++ main.cxx + flukam.f
SUBROUTINE FLUKAM (IFLGEO) REAL *8 AA, BB COMMON /AAAAAA/ AA,BB,II,JJ AA = 1. BB = 2. II = 10 JJ = 20 ICODE = 100 MREG = 17 CALL MGDRAW (ICODE,MREG) RETURN END
#include “header.h”
int main () { flukam (0); return (0); }

9. Mixing FORTRAN and C++ mgdraw.cxx
#include <iostream.h> #include <iomanip.h> #include “header.h”
#ifndef WIN32 #define flukam flukam_ #else #define flukam FLUKAM #endif
extern “C” { void mgdraw (int& icode, int& mreg) { cout << “ ICODE=” << icode << “ MREG=” << mreg << endl; cout << “ AA=” << AAAAAA.aa << “ BB=” << AAAAAA.bb << endl; cout << “ II=” << AAAAAA.ii << “ JJ=” << AAAAAA.jj << endl; } }

10. Mixing FORTRAN and C++ compiling and linking
g++ -c main.cxx
g++ -c mgdraw.cxx
g77 -c flukam.f
g++ -o mixedprog main.o mgdraw.o flukam.o
mixedprog
========================== Results =======================
ICODE=100 MREG=17
AA=1. BB=2.
II=10 JJ=20

11. Mixing FLUKA and ROOT compiling and linking
In the C++ user routine include
all necessary header files of ROOT, e.g. #include “...../root/include/TObject.h”
all header files containing variables of COMMONs to be used, e.g. #include “ /fluka/flukacppheaders/Ftrackr.h”
Modify the lfluka linker file
replace g77 by g++
Add library g2c $F77 $FFLAGS l${LIBF} ${LIBA} -lg2c