一个字符串hash算法

* Generic hash function to calculate a hash code from the given string.
 *
 * For each byte of the string, this function left-shifts the value in an
 * accumulator and then adds the byte into the accumulator.  The contents of
 * the accumulator is returned after the entire string has been processed.
 * It is assumed that this result will be used as the "hashcode" parameter in
 * calls to other functions in this package.  These functions automatically
 * adjust the hashcode for the size of each hashtable.
 *
 * This algorithm probably works best when the hash table size is a prime
 * number.
 *
 * Hopefully, this function is better than the previous one which returned
 * the sum of the squares of all the bytes.  I'm still open to other
 * suggestions for a default hash function.  The programmer is more than
 * welcome to supply his/her own hash function as that is one of the design
 * features of this package.

unsigned long
hash_HashFunction_s(const unsigned char *string, unsigned long len)
{
  register unsigned long accum; /*lint !e961*/

  accum = 0;

  for (; len > 0UL; len--)
    {
      accum <<= 1;
      accum += (unsigned long) (*string++ & 0xFF);
    }

  return accum;
}