                     fatalError("Patalogical size of compressed block.")
                 }
                 let blockSize = UInt32(truncatingIfNeeded: compressedBlock.count)
-                for i in 0..<4 {
+                for i:UInt32 in 0..<4 {
                     out.append(UInt8(truncatingIfNeeded: (blockSize & (0xFF << (i * 8))) >> (i * 8)))
                 }
                 out.append(contentsOf: compressedBlock)

                    fatalError("Patalogical size of non-compressible block.")
                }
                let blockSize = (0x80000000 as UInt32) | UInt32(truncatingIfNeeded: blockData.count)
                for i in 0..<4 {
                    out.append(UInt8(truncatingIfNeeded: (blockSize & (0xFF << (i * 8))) >> (i * 8)))
                }
                out.append(contentsOf: blockData)


            if blockChecksums {
                let blockChecksum = XxHash32.hash(data: Data(compressedBlock))
                for i: UInt32 in 0..<4 {
                    out.append(UInt8(truncatingIfNeeded: (blockChecksum & (0xFF << (i * 8))) >> (i * 8)))
                }
            }
