hsearch_r函数

inthsearch_r (item, action, retval, htab)     ENTRY item;     ACTION action;     ENTRY **retval;     struct hsearch_data *htab;{  unsigned int hval;  unsigned int count;  unsigned int len = strlen (item.key);  unsigned int idx;  /** Compute an value for the given string. Perhaps use a better method. */  hval = len;  count = len;  while (count-- > 0)    {      hval <<= 4;      hval += item.key[count];    }  /** First hash function: simply take the modul but prevent zero. */  idx = hval % htab->size + 1;  if (htab->table[idx].used)    {      /** Further action might be required according to the action value. */      if (htab->table[idx].used == hval && strcmp (item.key, htab->table[idx].entry.key) == 0){ *retval = &htab->table[idx].entry; return 1;}      /** Second hash function, as suggested in [Knuth] */      unsigned int hval2 = 1 + hval % (htab->size - 2);      unsigned int first_idx = idx;      do{ /** Because SIZE is prime this guarantees to step through all             available indeces.  */          if (idx <= hval2)   idx = htab->size + idx - hval2; else   idx -= hval2; /** If we visited all entries leave the loop unsuccessfully.  */ if (idx == first_idx)   break;            /** If entry is found use it. */          if (htab->table[idx].used == hval     && strcmp (item.key, htab->table[idx].entry.key) == 0)   {     *retval = &htab->table[idx].entry;     return 1;   }}      while (htab->table[idx].used);    }  /** An empty bucket has been found. */  if (action == ENTER)    {      /** If table is full and another entry should be entered returnwith error.  */      if (htab->filled == htab->size){ __set_errno (ENOMEM); *retval = NULL; return 0;}      htab->table[idx].used  = hval;      htab->table[idx].entry = item;      ++htab->filled;      *retval = &htab->table[idx].entry;      return 1;    }  __set_errno (ESRCH);  *retval = NULL;  return 0;}

函数执行的时候不论action为什么，先查找，若是命中则返回有的，若是没有命中节点且action为ENTER则进行hash_add操作。