How do I get a unique 8 character string from a 24 character string?

Assuming your 24 char string is upper+lower alpha-numeric, that'd be\n\n26+26+10 chars = 62 chars = 6 bits required to present them, and\n24 * 6 = 144 bits to store them.\n\n\n144bits/8bits/byte = 18 bytes. you cannot compress your 24 chars into 8 characters without having a potential collision. 8 chars at 8bits/char = 64bits maximum.",

8 is too few.\n\nHere is how you can get 16 from 24:\n\n$id = '507f191e810c19729de860ea';\n\n$str = base64_encode(implode('', array_map(function($c) { return chr(hexdec($c)); }, str_split($id, 2))));\n\nvar_dump($str); // UH8ZHoEMGXKd6GDq\n\n\nFor less characters you need to have bigger character base, but the thing is - there are no url safe left.",