Subversion Repositories uuid_mac_utils

                                        Structure of data (74 bits):

                                        - OPTIONAL : Sub-millisecond timestamp fraction (0-12 bits)

                                        - OPTIONAL : Carefully seeded counter

                                        - Random generated bits for any remaining space

                                        Since we don't know if timestamp fraction or counters are implemented

                                        (and if so, how many bits), we don't decode this information

        // Optional: millisecond fraction (max 12 bits)

        if (($num_ms_frac_bits < 0) || ($num_ms_frac_bits > 12)) throw new Exception("Invalid msec frac bits (must be 0..12)");

        if ($num_ms_frac_bits > 0) {

                $seconds_fraction = (float)explode(' ',microtime(false))[0];

                $nanoseconds_fraction = $seconds_fraction * 1000000;

                $resolution_ns = 1000000 / pow(2,$num_ms_frac_bits);

                $val = (int)ceil($nanoseconds_fraction / $resolution_ns);

                // Currently, for the output we only allow frac bits 0, 4, 8, 12 (0-3 nibbles),

                // since UUIDs are usually sorted in their hex notation

                $num_nibbles = (int)ceil($num_ms_frac_bits/4);

                $nibble_string = str_pad(dechex($val), $num_nibbles, '0', STR_PAD_LEFT);

                $uuid_nibbles .= $nibble_string;

        } else {

                $resolution_ns = 1000000;

        }

        // TODO Not implemented: Optional counter (to be defined as parameter to this method)

        // The counter bits need to be spread before and after the variant bits

        // Fill with random bits (and the variant bits)

        $uuid = gen_uuid_random();

        $uuid = str_replace('-', '', $uuid);

        for ($i=0; $i<strlen($uuid_nibbles); $i++) $uuid[$i] = $uuid_nibbles[$i];

        // Wait to make sure that the time part changes if multiple UUIDs are generated

        // We don't use usleep(), because it often does not sleep long enough!

        //       $resolution_us = (int)ceil($resolution_ns/1000);

        //       if ($resolution_us > 0) usleep($resolution_us);

        // We use this naive approach instead:

        if ($num_ms_frac_bits > 0) {

                $seconds_fraction = (float)explode(' ',microtime(false))[0];

                $nanoseconds_fraction = $seconds_fraction * 1000000;

                $resolution_ns = 1000000 / pow(2,$num_ms_frac_bits);

                $val = (int)ceil($nanoseconds_fraction / $resolution_ns);

                do {

                        $seconds_fraction = (float)explode(' ',microtime(false))[0];

                        $nanoseconds_fraction = $seconds_fraction * 1000000;

                        $resolution_ns = 1000000 / pow(2,$num_ms_frac_bits);

                        $val2 = (int)ceil($nanoseconds_fraction / $resolution_ns);

                } while ($val == $val2);

        } else {

                $unix_ts = dechex((int)ceil(microtime(true)*1000));

                do {

                        $unix_ts2 = dechex((int)ceil(microtime(true)*1000));

                } while ($unix_ts == $unix_ts2);

        }

        // Output

               substr($uuid,  8, 4).'-'.

               substr($uuid, 12, 4).'-'.

               substr($uuid, 16, 4).'-'.

               substr($uuid, 20, 12);