Which PHP function uses such hash algorithm?

Question

   1. static inline ulong zend_inline_hash_func(char *arKey, uint nKeyLength)
   2. {
   3.     register ulong hash = 5381;
   4.  
   5.     /* variant with the hash unrolled eight times */
   6.     for (; nKeyLength >= 8; nKeyLength -= 8) {
   7.         hash = ((hash << 5) + hash) + *arKey++;
   8.         hash = ((hash << 5) + hash) + *arKey++;
   9.         hash = ((hash << 5) + hash) + *arKey++;
  10.         hash = ((hash << 5) + hash) + *arKey++;
  11.         hash = ((hash << 5) + hash) + *arKey++;
  12.         hash = ((hash << 5) + hash) + *arKey++;
  13.         hash = ((hash << 5) + hash) + *arKey++;
  14.         hash = ((hash << 5) + hash) + *arKey++;
  15.     }
  16.     switch (nKeyLength) {
  17.         case 7: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */
  18.         case 6: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */
  19.         case 5: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */
  20.         case 4: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */
  21.         case 3: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */
  22.         case 2: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */
  23.         case 1: hash = ((hash << 5) + hash) + *arKey++; break;
  24.         case 0: break;
  25. EMPTY_SWITCH_DEFAULT_CASE()
  26.     }
  27.     return hash;
  28. }

Artefacto · Accepted Answer · 2010-11-19 07:52:58Z

4

All the hash tables use that hashing algorithm; hash tables in PHP are used, for instance, to implement arrays and symbol tables, among many other things.

The algorithm, as pointed in the header is DJBX33A (Daniel J. Bernstein, Times 33 with Addition).

answered Nov 19, 2010 at 7:52

Artefacto

98.1k17 gold badges207 silver badges230 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

ajx Over a year ago

So it's only used internally by PHP,without such an api for PHP users?

BoltClock Over a year ago

I was going to answer with this too, but wasn't sure and got lost looking for sources. Looks like you confirmed it, +1

Artefacto Over a year ago

@ajx As far as I know there's no API for user-land.

nikita2206 Over a year ago

@ajx It's easily implemented in PHP: $key = "string to hash"; $hash = 5381; for ($len = strlen($key), $i = 0; $i < $len; $i++) { $hash = $hash * 33 + ord($key[$i]); }

Pacerier Over a year ago

@Artefacto, Why is this algorithm chosen instead of the one Java uses s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]?

an_animal · Accepted Answer · 2013-03-18 20:49:39Z

1

You can use this link to see where this function is used: http://lxr.php.net/search?q=+zend_inline_hash_func&defs=&refs=&path=&hist=&project=PHP_5_4

looks like there are 3 php extensions (including standard) where this function is used.

answered Mar 18, 2013 at 20:49

an_animal

866 bronze badges

Collectives™ on Stack Overflow

Which PHP function uses such hash algorithm?

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related