## 0.10.4 (2023-03-09)
### Fixed
- Unsoundness triggered by zero block size  ([#844])

[#844]: https://github.com/RustCrypto/utils/pull/844

use core::{fmt, marker::PhantomData, slice};
use generic_array::{
    typenum::{IsLess, Le, NonZero, U256},
    ArrayLength, GenericArray,
};

pub struct BlockBuffer<BlockSize, Kind>
where
    BlockSize: ArrayLength<u8> + IsLess<U256>,
    Le<BlockSize, U256>: NonZero,
    Kind: BufferKind,
{
    buffer: Block<BlockSize>,
    pos: u8,
    _pd: PhantomData<Kind>,
}

    fn default() -> Self {
        if BlockSize::USIZE == 0 {
            panic!("Block size can not be equal to zero");
        }
        Self {
            buffer: Default::default(),
            pos: 0,
            _pd: PhantomData,
        }
    }
}

    /// Return current cursor position.
    #[inline(always)]
    pub fn get_pos(&self) -> usize {
        let pos = self.pos as usize;
        if !Kind::invariant(pos, BlockSize::USIZE) {
            debug_assert!(false);
            // SAFETY: `pos` never breaks the invariant
            unsafe {
                core::hint::unreachable_unchecked();
            }
        }
        pos
    }

#[inline(always)]
fn to_blocks_mut<N: ArrayLength<u8>>(data: &mut [u8]) -> (&mut [Block<N>], &mut [u8]) {
    let nb = data.len() / N::USIZE;
    let (left, right) = data.split_at_mut(nb * N::USIZE);
    let p = left.as_mut_ptr() as *mut Block<N>;
    // SAFETY: we guarantee that `blocks` does not point outside of `data`, and `p` is valid for
    // mutation
    let blocks = unsafe { slice::from_raw_parts_mut(p, nb) };
    (blocks, right)
}

    pub fn digest_blocks(
        &mut self,
        mut input: &[u8],
        mut compress: impl FnMut(&[Block<BlockSize>]),
    ) {
        let pos = self.get_pos();
        // using `self.remaining()` for some reason
        // prevents panic elimination
        let rem = self.size() - pos;
        let n = input.len();
        // Note that checking condition `pos + n < BlockSize` is
        // equivalent to checking `n < rem`, where `rem` is equal
        // to `BlockSize - pos`. Using the latter allows us to work
        // around compiler accounting for possible overflow of
        // `pos + n` which results in it inserting unreachable
        // panic branches. Using `unreachable_unchecked` in `get_pos`
        // we convince compiler that `BlockSize - pos` never underflows.
        if Kind::invariant(n, rem) {
            // double slicing allows to remove panic branches
            self.buffer[pos..][..n].copy_from_slice(input);
            self.set_pos_unchecked(pos + n);
            return;
        }
        if pos != 0 {
            let (left, right) = input.split_at(rem);
            input = right;
            self.buffer[pos..].copy_from_slice(left);
            compress(slice::from_ref(&self.buffer));
        }

        let (blocks, leftover) = Kind::split_blocks(input);
        if !blocks.is_empty() {
            compress(blocks);
        }

        let n = leftover.len();
        self.buffer[..n].copy_from_slice(leftover);
        self.set_pos_unchecked(n);
    }

    pub fn digest_pad(
        &mut self,
        delim: u8,
        suffix: &[u8],
        mut compress: impl FnMut(&Block<BlockSize>),
    ) {
        if suffix.len() > BlockSize::USIZE {
            panic!("suffix is too long");
        }
        let pos = self.get_pos();
        self.buffer[pos] = delim;
        for b in &mut self.buffer[pos + 1..] {
            *b = 0;
        }

        let n = self.size() - suffix.len();
        if self.size() - pos - 1 < suffix.len() {
            compress(&self.buffer);
            let mut block = Block::<BlockSize>::default();
            block[n..].copy_from_slice(suffix);
            compress(&block);
        } else {
            self.buffer[n..].copy_from_slice(suffix);
            compress(&self.buffer);
        }
        self.set_pos_unchecked(0)
    }

    /// Pad message with 0x80, zeros and 64-bit message length using
    /// big-endian byte order.
    #[inline]
    pub fn len64_padding_be(&mut self, data_len: u64, compress: impl FnMut(&Block<BlockSize>)) {
        self.digest_pad(0x80, &data_len.to_be_bytes(), compress);
    }

    /// Pad message with 0x80, zeros and 64-bit message length using
    /// little-endian byte order.
    #[inline]
    pub fn len64_padding_le(&mut self, data_len: u64, compress: impl FnMut(&Block<BlockSize>)) {
        self.digest_pad(0x80, &data_len.to_le_bytes(), compress);
    }

    /// Pad message with 0x80, zeros and 128-bit message length using
    /// big-endian byte order.
    #[inline]
    pub fn len128_padding_be(&mut self, data_len: u128, compress: impl FnMut(&Block<BlockSize>)) {
        self.digest_pad(0x80, &data_len.to_be_bytes(), compress);
    }
}

    #[inline(always)]
    fn split_blocks<N: ArrayLength<u8>>(data: &[u8]) -> (&[Block<N>], &[u8]) {
        let nb = data.len() / N::USIZE;
        let blocks_len = nb * N::USIZE;
        let tail_len = data.len() - blocks_len;
        // SAFETY: we guarantee that created slices do not point
        // outside of `data`
        unsafe {
            let blocks_ptr = data.as_ptr() as *const Block<N>;
            let tail_ptr = data.as_ptr().add(blocks_len);
            (
                slice::from_raw_parts(blocks_ptr, nb),
                slice::from_raw_parts(tail_ptr, tail_len),
            )
        }
    }
}

impl Sealed for super::Lazy {
    #[inline(always)]
    fn invariant(pos: usize, block_size: usize) -> bool {
        pos <= block_size
    }

    #[inline(always)]
    fn split_blocks<N: ArrayLength<u8>>(data: &[u8]) -> (&[Block<N>], &[u8]) {
        if data.is_empty() {
            return (&[], &[]);
        }
        let (nb, tail_len) = if data.len() % N::USIZE == 0 {
            (data.len() / N::USIZE - 1, N::USIZE)
        } else {
            let nb = data.len() / N::USIZE;
            (nb, data.len() - nb * N::USIZE)
        };
        let blocks_len = nb * N::USIZE;
        // SAFETY: we guarantee that created slices do not point
        // outside of `data`
        unsafe {
            let blocks_ptr = data.as_ptr() as *const Block<N>;
            let tail_ptr = data.as_ptr().add(blocks_len);
            (
                slice::from_raw_parts(blocks_ptr, nb),
                slice::from_raw_parts(tail_ptr, tail_len),
            )
        }
    }
}