# function patterns_utils_get_uuuid in Patterns 7.2

Generates a Universally Unique IDentifier, version 4.

RFC 4122 (http://www.ietf.org/rfc/rfc4122.txt) defines a special type of Globally Unique IDentifiers (GUID), as well as several methods for producing them. One such method, described in section 4.4, is based on truly random or pseudo-random number generators, and is therefore implementable in a language like PHP.

We choose to produce pseudo-random numbers with the Mersenne Twister, and to always limit single generated numbers to 16 bits (ie. the decimal value 65535). That is because, even on 32-bit systems, PHP's RAND_MAX will often be the maximum *signed* value, with only the equivalent of 31 significant bits. Producing two 16-bit random numbers to make up a 32-bit one is less efficient, but guarantees that all 32 bits are random.

The algorithm for version 4 UUIDs (ie. those based on random number generators) states that all 128 bits separated into the various fields (32 bits, 16 bits, 16 bits, 8 bits and 8 bits, 48 bits) should be random, except : (a) the version number should be the last 4 bits in the 3rd field, and (b) bits 6 and 7 of the 4th field should be 01. We try to conform to that definition as efficiently as possible, generating smaller values where possible, and minimizing the number of base conversions.

@copyright Copyright (c) CFD Labs, 2006. This function may be used freely for any purpose ; it is distributed without any form of warranty whatsoever. @author David Holmes <dholmes@cfdsoftware.net>

### Return value

string A UUID, made up of 32 hex digits and 4 hyphens.

## 1 call to patterns_utils_get_uuuid()

- patterns_db_save_pattern in includes/
db.inc - Writes the pattern metadata (and the actual pattern) to the database.

### File

- includes/
utils.inc, line 431 - Collectiion of general purpose functions.

### Code

```
function patterns_utils_get_uuuid() {
// The field names refer to RFC 4122 section 4.1.2
return sprintf('%04x%04x-%04x-%03x4-%04x-%04x%04x%04x', mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 4095), bindec(substr_replace(sprintf('%016b', mt_rand(0, 65535)), '01', 6, 2)), mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535));
}
```