Proper v7 subsec encoding (#32)

Author: oittaa

README.md

@@ -60,7 +60,7 @@ var_dump($uuid6_first < $uuid6_second); // bool(true)
 
 // Generate a version 7 (lexicographically sortable) UUID
 $uuid7_first = UUID::uuid7();
-echo $uuid7_first . "\n"; // e.g. 061a3d43-61d0-7cf4-bfce-753dadab55e1
+echo $uuid7_first . "\n"; // e.g. 061d0edc-bea0-75cc-9892-f6295fd7d295
 $uuid7_second = UUID::uuid7();
 var_dump($uuid7_first < $uuid7_second); // bool(true)
 
@@ -114,8 +114,8 @@ var_dump($cmp3 === 0); // bool(true)
 // Extract Unix time from versions 6 and 7 as a string.
 $uuid6_time = UUID::getTime('1ebacf4f-a4a8-68ee-b4ec-618c14d005d5');
 var_dump($uuid6_time); // string(18) "1620145373.6118510"
-$uuid7_time = UUID::getTime('061a3d43-61d0-7cf4-bfce-753dadab55e1');
-var_dump($uuid7_time); // string(18) "1638126646.1903860"
+$uuid7_time = UUID::getTime('061d0edc-bea0-75cc-9892-f6295fd7d295');
+var_dump($uuid7_time); // string(18) "1641082315.9141510"
 
 // Extract the UUID version.
 $uuid_version = UUID::getVersion('2140a926-4a47-465c-b622-4571ad9bb378');

src/UUID.php

@@ -134,6 +134,18 @@ private static function uuidFromHex(string $uhex, int $version): string
         );
     }
 
+    /** @internal */
+    private static function encodeSubsec(int $value): int
+    {
+        return intdiv($value * 2 ** 24, 10 ** 7);
+    }
+
+    /** @internal */
+    private static function decodeSubsec(int $value): int
+    {
+        return (int) ceil($value * 10 ** 7 / 2 ** 24);
+    }
+
     /**
      * Generate a version 3 UUID based on the MD5 hash of a namespace identifier
      * (which is a UUID) and a name (which is a string).
@@ -201,6 +213,7 @@ public static function uuid6(): string
     public static function uuid7(): string
     {
         [$unixts, $subsec] = self::getUnixTime();
+        $subsec = self::encodeSubsec($subsec);
         $uhex = substr(str_pad(dechex($unixts), 9, '0', \STR_PAD_LEFT), -9);
         $uhex .= substr_replace(str_pad(dechex($subsec), 6, '0', \STR_PAD_LEFT), '7', -3, 0);
         $uhex .= bin2hex(random_bytes(8));
@@ -246,7 +259,7 @@ public static function getTime(string $uuid): ?string
             $retval = substr_replace(strval(hexdec($timehex) - self::TIME_OFFSET_INT), '.', -7, 0);
         } elseif ($version === 7) {
             $unixts = hexdec(substr($timehex, 0, 10));
-            $subsec = str_pad(strval(hexdec(substr($timehex, 10))), 7, '0', \STR_PAD_LEFT);
+            $subsec = str_pad(strval(self::decodeSubsec(hexdec(substr($timehex, 10)))), 7, '0', \STR_PAD_LEFT);
             $retval = $unixts . '.' . $subsec;
         }
         return $retval;

tests/UuidTest.php

@@ -191,8 +191,8 @@ public function testKnownGetTime()
     {
         $uuid6_time = UUID::getTime('1ebacf4f-a4a8-68ee-b4ec-618c14d005d5');
         $this->assertSame($uuid6_time, '1620145373.6118510');
-        $uuid7_time = UUID::getTime('061a3d43-61d0-7cf4-bfce-753dadab55e1');
-        $this->assertSame($uuid7_time, '1638126646.1903860');
+        $uuid7_time = UUID::getTime('061d0edc-bea0-75cc-9892-f6295fd7d295');
+        $this->assertSame($uuid7_time, '1641082315.9141510');
     }
 
     public function testGetTimeValid()