blake2b 0.6.1

BLAKE2b hash function
Documentation 
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use {Hash, ParameterBlock, compress, IV};
use slice_ext::{SliceExt};

#[derive(Clone, Debug)]
pub struct Blake2b {
	hash: [u64; 8],
	counter: (u64, u64),
	len: usize
}

impl Blake2b {
	pub fn new(len: usize) -> Self {
		Self::with_parameter_block(len, ParameterBlock::new().set_digest_len(len as u8).set_fanout(1).set_max_depth(1))
	}

	pub fn with_parameter_block(len: usize, parameter_block: ParameterBlock) -> Self {
		assert!(len >= 1 && len <= 64, "len must be >= 1 and <= 64");

		let mut hash = parameter_block.0;
		for (a, b) in hash.iter_mut().zip(IV.iter()) {
			*a ^= *b;
		}

		Blake2b {
			hash: hash,
			counter: (0, 0),
			len: len
		}
	}

	pub fn len(&self) -> usize {
		self.len
	}

	pub fn update(&mut self, block: &[u64; 16]) {
		self.add_counter(128);
		compress(block, &mut self.hash, self.counter, (0, 0));
	}

	pub fn finish(mut self, block: &[u64; 16], len: usize) -> Hash {
		assert!(len <= 128);
		debug_assert!(block.as_bytes()[len..].iter().all(|&i| i == 0));

		self.add_counter(len as u64);
		compress(block, &mut self.hash, self.counter, (!0, 0));
		Hash::new(self.hash, self.len)
	}

	fn add_counter(&mut self, v: u64) {
		debug_assert!(v <= 128);

		let (v, b) = self.counter.0.overflowing_add(v);
		self.counter.0 = v;
		if b {
			self.counter.1 = self.counter.1.checked_add(1).expect("blake2b counter overflowed");
		}
	}
}

impl Default for Blake2b {
	fn default() -> Self {
		Self::new(64)
	}
}