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# 1  
Old 10-28-2014
Hash Table
I was looking at this script and was wondering if anyone can explain what this script does and how does it work. Thank you for any help.

Code:
State* lookup(char* prefix[NPREF], int create)

{

     int i, h;

     State *sp = NULL ;

     h = hash(prefix);

     for (sp = statetab[h]; sp != NULL; sp = sp->next) {

     for (i = 0; i < NPREF; i++)

     if (strcmp(prefix[i], sp->pref[i]) != 0)

     if (i == NPREF) /* found it */

     return sp;

     break;

}

     if (create) {

          sp = (State*) emalloc( sizeof( State ));

          for( i=0; i<NPREF; i++ )

          sp->pref[i] = prefix[i];

          sp->suf = NULL;

          sp->next = statetab[h];

          statetab[h] = sp;

     }

     return sp;

}

# 2  
Old 10-30-2014
Indentation helps:
Code:
State* lookup(char* prefix[NPREF], int create)
 
{
 
     int i, h;
 
     State *sp = NULL ;
 
     h = hash(prefix);
 
     for (sp = statetab[h]; sp != NULL; sp = sp->next) {
 
       for (i = 0; i < NPREF; i++)
 
         if (strcmp(prefix[i], sp->pref[i]) != 0)
 
           if (i == NPREF) /* found it */
 
             return sp;
 
       break;
 
     }
 
     if (create) {
 
          sp = (State*) emalloc( sizeof( State ));
 
          for( i=0; i<NPREF; i++ )
 
            sp->pref[i] = prefix[i];
 
          sp->suf = NULL;
 
          sp->next = statetab[h];
 
          statetab[h] = sp;
 
     }
 
     return sp;
 
}

Hash table (no payload, just keys) insert unique (i.e., if not already). Hash table - Wikipedia, the free encyclopedia Very odd contents match logic! What language?
# 3  
Old 10-30-2014
It's C. Not shell.
# 4  
Old 10-30-2014
Quote:
Originally Posted by DGPickett
Indentation helps:[CODE]Very odd contents match logic! What language?
Yes, I don't think this code will ever match anything:

Code:
       for (i = 0; i < NPREF; i++)
 
         if (strcmp(prefix[i], sp->pref[i]) != 0)
 
           if (i == NPREF) /* found it */
 
             return sp;

The variable i should never be == to NPREF within that loop.
# 5  
Old 10-30-2014
Moderator's Comments:
Mod Comment This thread has been moved and renamed. As pointed out by MadeInGermany, this C code; not a shell script.
# 6  
Old 10-30-2014
How does it work? It words badly, if at all.

That is some seriously broken code. Even if the match code is fixed, it will only examine the first State *sp pointer because of the break statement in the outer for loop.

And then, if create is non-zero and the upper loops didn't find a match at the first node, it will stuff the passed-in data onto the hash table even if it already exists further down the linked list.
# 7  
Old 10-31-2014
Yes, although PERL and python can look a lot like C, I figured C.

It does seem to be a find/optional insert if missing, hash map/table routine, with linked list buckets, but I am not familiar with passing an array and its length that way. It seems like if the elements char* can be copied, why not just copy the array char** to a pointer element? Let's try something more simple and legal:
Code:
State* lookup( char* prefix[], size_t NPREF, int create ){
     int i, h;
     State *sp = NULL ;
 
     h = hash(prefix);
 
     for ( sp = statetab[h]; sp != NULL; sp = sp->next ){
       for  (i = 0; i < NPREF; i++ )
         if ( strcmp( prefix[i], sp->pref[i] ) != 0 )
           break ;
 
       if ( i == NPREF ) /* found it */ 
             return sp;
     }
 
     if (create) {
          sp = (State*) emalloc( sizeof( State ));
          sp->pre = prefix ;
          sp->suf = NULL;
          sp->next = statetab[h];
          statetab[h] = sp;
      }
 
     return sp;
 }

It'd be nice if it had the call format like bsearch, tsearch but then it would be hsearch()! https://www.unix.com/man-page/opensolaris/3c/hsearch/
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