3v4l.org

run code in 300+ PHP versions simultaneously
<?php var_dump( bin2hex( mb_convert_encoding( "\xf4\x90\xbf\xbf", 'UTF-16BE', 'UTF-8' ) ) );
Output for 5.4.20 - 5.4.45, 5.5.2 - 5.5.38, 5.6.0 - 5.6.38, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.6 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
string(16) "003f003f003f003f"
Output for 5.4.0 - 5.4.19, 5.5.0 - 5.5.1, 8.1.0 - 8.1.5
string(12) "003f003f003f"
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29
string(8) "dc03dfff"

preferences:
330.62 ms | 402 KiB | 448 Q