dogensym voodoo - Pd-dev

6 Sep 2013


      Hi list,
Can someone explain the symhash voodoo in the dogensym function of
m_class.c?
To me it looks like sym1 could be referring to a location in
the symhash array which isn't yet initialized, so I can't
wrap my head around why sym2->s_name doesn't just
crash Pd.
Code below for easy reference:
/* ---------------- the symbol table ------------------------ */
#define HASHSIZE 1024
static t_symbol *symhash[HASHSIZE];
t_symbol *dogensym(const char *s, t_symbol *oldsym)
{
     t_symbol **sym1, *sym2;
     unsigned int hash1 = 0,  hash2 = 0;
     int length = 0;
     const char *s2 = s;
     while (*s2)
     {
         hash1 += *s2;
         hash2 += hash1;
         length++;
         s2++;
     }
     sym1 = symhash + (hash2 & (HASHSIZE-1));
     while (sym2 = *sym1)
     {
         if (!strcmp(sym2->s_name, s)) return(sym2);
         sym1 = &sym2->s_next;
     }
     if (oldsym) sym2 = oldsym;
     else
     {
         sym2 = (t_symbol *)t_getbytes(sizeof(*sym2));
         sym2->s_name = t_getbytes(length+1);
         sym2->s_next = 0;
         sym2->s_thing = 0;
         strcpy(sym2->s_name, s);
     }
     *sym1 = sym2;
     return (sym2);
}