UUID+ascii85.swift

private extension UUID {
   /// a more concise representation of UUIDs
   var ascii85: String {
       func convert(_ a: UInt8, _ b: UInt8, _ c: UInt8, _ d: UInt8) -> [UInt8] {
           if a == 0, b == 0, c == 0, d == 0 {
               return [122] // "z"
           }

           let x = UInt(a) * 52200625 + UInt(b) * 614125 + UInt(c) * 7225 + UInt(d)

           let c0 = UInt8((x / 52200625) % 85) + 33
           let c1 = UInt8((x / 614125) % 85) + 33
           let c2 = UInt8((x / 7225) % 85) + 33
           let c3 = UInt8((x / 85) % 85) + 33
           let c4 = UInt8(x % 85) + 33

           return [c0,c1,c2,c3,c4]
       }

       var aa = convert(uuid.0, uuid.1, uuid.2, uuid.3)
       aa += convert(uuid.4, uuid.5, uuid.6, uuid.7)
       aa += convert(uuid.8, uuid.9, uuid.10, uuid.11)
       aa += convert(uuid.12, uuid.13, uuid.14, uuid.15)
       return String(cString: aa)
   }
}