Thread: Hash function... translated from C++

Hey,
I am trying to translate a C++ implementation of the DJB Hash function into C.
Here is the original:

Code:

unsigned int DJBHash(const std::string& str)
{
   unsigned int hash = 5381;

   for(std::size_t i = 0; i < str.length(); i++)
   {
      hash = ((hash << 5) + hash) + str[i];
   }

   return (hash & 0x7FFFFFFF);
}

would the following code in C work, I'm confused about a few features...

Code:

unsigned int DJBHash(unsigned char *str)
{
   unsigned int hash = 5381;

   for(unsigned int i = 0; i < strlen(str); i++)
   {
      hash = ((hash << 5) + hash) + str[i];
   }

   return (hash & 0x7FFFFFFF);
}

My main confusion is the "<<" operator. Thanks

Code:

unsigned int DJBHash(unsigned char *str)
{
   unsigned int hash = 5381;
   int n = strlen(str);

   for(unsigned int i = 0; i < n; i++)
   {
      hash = ((hash << 5) + hash) + str[i];
   }

   return (hash & 0x7FFFFFFF);
}

So this should fix the inefficiency problem.
Not sure exactly what you meant in Point 1, Salem. This function in C will stop at the first null terminator. ...?

Is this code now right?
Thanks

Oh ok, I see. But this should not be a problem if I know my string does not contain embedded null characters?

Also, what does 0x7FFFFFFF add to the return?
return (hash & 0x7FFFFFFF);

what do you mean they should be size_t... sorry, not familiar.
Do you mean rather than declaring them as int, they should be size_t?

what would that look like in context?

Thanks for the help!

Code:

unsigned int DJBHash(unsigned char *str)
{
   unsigned int hash = 5381;
size_t i;   
size_t n = strlen(str);

   for(i = 0; i < n; i++)
   {
      hash = ((hash << 5) + hash) + str[i];
   }

   return (hash & 0x7FFFFFFF);
}

Is this what you mean?