ccr/uuid.php

   1 <?php
   2 /*
   3  * Generates a Universally Unique IDentifier, version 4.
   4  *
   5  * RFC 4122 (http://www.ietf.org/rfc/rfc4122.txt) defines a special type of Globally
   6  * Unique IDentifiers (GUID), as well as several methods for producing them. One
   7  * such method, described in section 4.4, is based on truly random or pseudo-random
   8  * number generators, and is therefore implementable in a language like PHP.
   9  *
  10  * We choose to produce pseudo-random numbers with the Mersenne Twister, and to always
  11  * limit single generated numbers to 16 bits (ie. the decimal value 65535). That is
  12  * because, even on 32-bit systems, PHP's RAND_MAX will often be the maximum *signed*
  13  * value, with only the equivalent of 31 significant bits. Producing two 16-bit random
  14  * numbers to make up a 32-bit one is less efficient, but guarantees that all 32 bits
  15  * are random.
  16  *
  17  * The algorithm for version 4 UUIDs (ie. those based on random number generators)
  18  * states that all 128 bits separated into the various fields (32 bits, 16 bits, 16 bits,
  19  * 8 bits and 8 bits, 48 bits) should be random, except : (a) the version number should
  20  * be the last 4 bits in the 3rd field, and (b) bits 6 and 7 of the 4th field should
  21  * be 01. We try to conform to that definition as efficiently as possible, generating
  22  * smaller values where possible, and minimizing the number of base conversions.
  23  *
  24  * @copyright  Copyright (c) CFD Labs, 2006. This function may be used freely for
  25  *              any purpose ; it is distributed without any form of warranty whatsoever.
  26  * @author      David Holmes <dholmes@cfdsoftware.net>
  27  *
  28  * @return  string  A UUID, made up of 32 hex digits and 4 hyphens.
  29  */
  30
  31 function getUuid()
  32 {
  33
  34    // The field names refer to RFC 4122 section 4.1.2
  35
  36     return sprintf(
  37         'A%04x%04x-%04x-%03x4-%04x-%04x%04x%04x',
  38         mt_rand(0, 65535),
  39         mt_rand(0, 65535), // 32 bits for "time_low"
  40         mt_rand(0, 65535), // 16 bits for "time_mid"
  41         mt_rand(0, 4095),  // 12 bits before the 0100 of (version) 4 for "time_hi_and_version"
  42         bindec(substr_replace(sprintf('%016b', mt_rand(0, 65535)), '01', 6, 2)),
  43         // 8 bits, the last two of which (positions 6 and 7) are 01, for "clk_seq_hi_res"
  44            // (hence, the 2nd hex digit after the 3rd hyphen can only be 1, 5, 9 or d)
  45            // 8 bits for "clk_seq_low"
  46         mt_rand(0, 65535),
  47         mt_rand(0, 65535),
  48         mt_rand(0, 65535) // 48 bits for "node"
  49     );
  50 }