Hash, use shift-folding snip

#include
#include
#include
#include

#define MAXLINE         128
#define HTABSIZE        101
#define NSHIFT          3

struct hnode {
 int pos;
 char *key;
 struct hnode *next;
};

typedef struct hnode *hashtable[HTABSIZE];

int  htab_key(char *key);
int  htab_getval(hashtable h, char *key);
void htab_insert(hashtable h, char *key, int pos);
void htab_dump(hashtable htab);
void htab_free(hashtable htab);

int main(int argc, char *argv[]) {
 char line[MAXLINE];
 hashtable htab = {0};
 int len = 0;
 int i = 0;
 int retv = 0;

 if(argc != 2)
  error(1, 0, "querry < input.txt");

 while(fgets(line, MAXLINE, stdin) != NULL) {
  /* strip newlines */
  len = strlen(line);
  if(line[len - 1] == '\n')
   line[--len] = '\0';

  if(len > 2)
   htab_insert(htab, line, i++);
 }

 if((retv = htab_getval(htab, argv[1])) == -1)
  printf("NOT found: `%s', `%d'\n", argv[1], retv);
 else
  printf("FOUND: `%s' at `%d'\n", argv[1], retv);

 /* htab_dump(htab); */
 htab_free(htab);

 return 0;
}

int htab_key(char *key) {
 char *ptr = NULL;
 int retv = 0;
 int i = 0;
 int x = 0;

 for(ptr = key; *ptr; retv += x)
  for(i = 0, x = 0; i < NSHIFT && *ptr; i++, ptr++)
   x = x * 10 + *ptr;

 retv %= HTABSIZE;
 return retv;
}

void htab_insert(hashtable htab, char *key, int pos) {
 struct hnode *ptr = (struct hnode *)malloc(sizeof(struct hnode));
 int index = htab_key(key);

 ptr->key = strdup(key);
 ptr->pos = pos;
 ptr->next = htab[index];

 htab[index] = ptr;
 return;
}

int htab_getval(hashtable htab, char *key) {
 struct hnode *ptr = {0};

 for(ptr = htab[htab_key(key)]; ptr && strcmp(ptr->key, key); ptr = ptr->next)
  ;

 if(ptr)
  return ptr->pos;
 else
  return -1;
}

void htab_dump(hashtable htab) {
 struct hnode *ptr = {0};
 int i = 0;

 for(i = 0; i < HTABSIZE; i++) {
  printf("[%02d]: ", i);
  for(ptr = htab[i]; ptr; ptr = ptr->next) {
   printf("[%d] -> %s", ptr->pos, ptr->key);
  }
  printf("\n");
 }

 return;
}

void htab_free(hashtable htab) {
 struct hnode *ptr = {0};
 struct hnode *tmp = {0};
 int i = 0;

 for(i = 0; i < HTABSIZE; i++) {
  for(ptr = htab[i]; ptr; ptr = ptr->next) {
   if(ptr->next != NULL) {
    free(ptr->key), tmp = ptr->next;
    free(ptr), ptr = tmp;
   }
  }
 }

 return;
}