note 65879 deleted from function.uniqid by googleguy

Note Submitter: dholmes at cfdsoftware dot net ---- WARNING : I believe there are a couple of mistakes in the function provided just below by maciej dot strzelecki at gmail dot com. Namely, that in the two substr_replace() calls, the third parameters should respectively be 12 (instead of 11) and 6 (instead of 5). Considering the importance of this function, I went to read RFC 4122 myself, and found the discrepancy. I therefore chose to write my own function, inspired by the previous one, but with a few enhancements detailed in the comments. On the downside, it might be slightly less easy to understand at first glance. Please feel free to use it yourself. Thank you also in advance for any feedback at dholmes at cfdsoftware.net . <?php /** * 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 string A UUID, made up of 32 hex digits and 4 hyphens. */ function uuid() { // 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), // 32 bits for "time_low" mt_rand(0, 65535), // 16 bits for "time_mid" mt_rand(0, 4095), // 12 bits before the 0100 of (version) 4 for "time_hi_and_version" bindec(substr_replace(sprintf('%016b', mt_rand(0, 65535)), '01', 6, 2)), // 8 bits, the last two of which (positions 6 and 7) are 01, for "clk_seq_hi_res" // (hence, the 2nd hex digit after the 3rd hyphen can only be 1, 5, 9 or d) // 8 bits for "clk_seq_low" mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535) // 48 bits for "node" ); } ?>