[C] Generatore random tra 0-1

[killercode]

Header

#define Norm_Factor 2.328306437080797e-10

#ifdef MACRO
#define Ranf() (((n1=n1->next)->Y += (n2=n2->next)->Y), (double)n1->Y * Norm_Factor)
#else
#define Ranf() rand55()
double rand55();
#endif

void rand_init(long);

typedef struct Lnk_List *Lnk_List_Ptr;
struct Lnk_List {
unsigned long Y;
Lnk_List_Ptr next;
} ;


File

#include <stdio.h>
#include <stdlib.h>
#include "rand55.h"

long Seed=161803398L;

Lnk_List_Ptr Ran, n1, n2;

#ifdef INLINE
inline
#endif
double rand55()
{
n1=n1->next;
n2=n2->next;
n1->Y += n2->Y;

return (double)n1->Y * Norm_Factor ;
}

void rand_init(long idum)
{
int i,j;
long tmp,aux;
double null;

if((Ran = (Lnk_List_Ptr)calloc(55,sizeof(struct Lnk_List)))==NULL)
exit(1);
for(i=0;i<54;++i) {
(Ran+i)->next = Ran+i+1;
}
(Ran+54)->next = Ran;
tmp = Seed + idum;
Ran[54].Y = tmp;
aux=1;
j=20;
for(i=0;i<54;++i,j+=21){
j%=55;
Ran[j].Y=aux;
aux+=tmp;
tmp=Ran[j].Y;
}

n1=Ran;
n2=Ran+31;

for(j=0;j<55*4;++j) {
null += rand55();
}
fprintf(stderr,"Rand55 initialized - chksum=%f\n",null);

}




Il file contenente la main semplicemente chiama fa funzione Ranf() e stampa il risultato. Le marco sono tutte a zero

Qualcuno mi spiegherebbe a cosa serve la funzione rand_init?
Grazie