package mtree import ( "bufio" "io" ) const posixPolynomial uint32 = 0x04C11DB7 func cksum(r io.Reader) (uint32, int, error) { in := bufio.NewReader(r) count := 0 var sum uint32 = 0 f := func(b byte) { for i := 7; i >= 0; i-- { msb := sum & (1 << 31) sum = sum << 1 if msb != 0 { sum = sum ^ posixPolynomial } } sum ^= uint32(b) } for done := false; !done; { switch b, err := in.ReadByte(); err { case io.EOF: done = true case nil: f(b) count++ default: return ^sum, count, err } } for m := count; ; { f(byte(m) & 0xff) m = m >> 8 if m == 0 { break } } f(0) f(0) f(0) f(0) return ^sum, count, nil }