PHP Fast UUIDv4

uuid4.php

function uuid4(): string
{
    return bin2hex(
        // 18 bytes encodes to 36 bytes. 32 for UUID + 4 for hyphens.
        // Bitwise AND to mask where static bits will be set
        // Mask and set UUID specific bits
        // In 00112233-4455-m677-n899-aabbccddeeff, m (4 bits) = version (4), n (2 bits) = variant (2)
        //                             00  11  22  33  -4  45  5-  m6  77  -n  89  9-  aa  bb  cc  dd  ee  ff
            (random_bytes(18) & "\xff\xff\xff\xff\x0f\xff\xf0\x0f\xff\x03\xff\xf0\xff\xff\xff\xff\xff\xff") |

        // Bitwise OR the version and varient fields of UUIDv4
        //        m=4  6      -    n=2
        // Mask   0000 1111   1111 0011
        // Bits   0100 0000   0000 1000
        //        ^^^4 ^^^0   ^^^0 ^^^8
        //                         ^2
            "\0\0\0\0\0\0\0\x40\0\x08\0\0\0\0\0\0\0\0"
            
        // Set hyphens at the correct positions. Hyphen locations are hex "0". "\x1d" is "0" ^ "-"
        ) ^ "\0\0\0\0\0\0\0\0\x1d\0\0\0\0\x1d\0\0\0\0\x1d\0\0\0\0\x1d\0\0\0\0\0\0\0\0\0\0\0\0";
}