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algorithmhashprimes

Reason for the number 5381 in the DJB hash function?

Can anyone tell me why the number 5381 is used in the DJB hash function?

The DJB hash function is defined as:

  • h 0 = 5381

  • h i = 33h i - 1 + s i

Here's a C implementation:

unsigned int DJBHash(char* str, unsigned int len)
{
   unsigned int hash = 5381;
   unsigned int i    = 0;

   for(i = 0; i < len; str++, i++)
   {   
      hash = ((hash << 5) + hash) + (*str);
   }   

   return hash;
}
Solution

  • 5381 is just a number that, in testing, resulted in fewer collisions and better avalanching. You'll find "magic constants" in just about every hash algo.