//! Cyclic redundancy check function.

fn crc_accum(a: u32, _: u32) -> u32
{
   if a & 1 == 1 {
      0xEDB8_8320 ^ a >> 1
   } else {
      a >> 1
   }
}

fn crc_init() -> [u32; 256]
{
   let mut t = [0; 256];
   for (n, v) in t.iter_mut().enumerate() {
      *v = (0..8).fold(n as u32, crc_accum);
   }
   t
}

pub fn crc32(b: &[u8], s: u32) -> u32
{
   let t = crc_init();
   !b.iter()
     .fold(s, |a, &o| a >> 8 ^ t[(a & 0xFF ^ u32::from(o)) as usize])
}

#[test]
fn crc32_lorem_ipsum()
{
   assert_eq!(crc32(b"Lorem ipsum dolor sit amet", !0), 0x5F29D461);
}

// EOF