//! Fixed size buffer for block processing of data.
#![no_std]
#![doc(
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html_favicon_url = "
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#![warn(missing_docs, rust_2018_idioms)]
pub use generic_array;
use core::{fmt, marker::PhantomData, slice};
use generic_array::{
typenum::{IsLess, Le, NonZero, U256},
ArrayLength, GenericArray,
};
mod sealed;
/// Block on which `BlockBuffer` operates.
pub type Block<BlockSize> = GenericArray<u8, BlockSize>;
/// Trait for buffer kinds.
pub trait BufferKind: sealed::Sealed {}
/// Eager block buffer kind, which guarantees that buffer position
/// always lies in the range of `0..BlockSize`.
#[derive(Copy, Clone, Debug, Default)]
pub struct Eager {}
/// Lazy block buffer kind, which guarantees that buffer position
/// always lies in the range of `0..=BlockSize`.
#[derive(Copy, Clone, Debug, Default)]
pub struct Lazy {}
impl BufferKind for Eager {}
impl BufferKind for Lazy {}
/// Eager block buffer.
pub type EagerBuffer<B> = BlockBuffer<B, Eager>;
/// Lazy block buffer.
pub type LazyBuffer<B> = BlockBuffer<B, Lazy>;
/// Block buffer error.
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub struct Error;
impl fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
f.write_str("Block buffer error")
}
}
/// Buffer for block processing of data.
#[derive(Debug)]
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>,
}
impl<BlockSize, Kind> Default for BlockBuffer<BlockSize, Kind>
where
BlockSize: ArrayLength<u8> + IsLess<U256>,
Le<BlockSize, U256>: NonZero,
Kind: BufferKind,
{
fn default() -> Self {
Self {
buffer: Default::default(),
pos: 0,
_pd: PhantomData,
}
}
}
impl<BlockSize, Kind> Clone for BlockBuffer<BlockSize, Kind>
where
BlockSize: ArrayLength<u8> + IsLess<U256>,
Le<BlockSize, U256>: NonZero,
Kind: BufferKind,
{
fn clone(&self) -> Self {
Self {
buffer: self.buffer.clone(),
pos: self.pos,
_pd: PhantomData,
}
}
}
impl<BlockSize, Kind> BlockBuffer<BlockSize, Kind>
where
BlockSize: ArrayLength<u8> + IsLess<U256>,
Le<BlockSize, U256>: NonZero,
Kind: BufferKind,
{
/// Create new buffer from slice.
///
/// # Panics
/// If slice length is not valid for used buffer kind.
#[inline(always)]
pub fn new(buf: &[u8]) -> Self {
Self::try_new(buf).unwrap()
}
/// Create new buffer from slice.
///
/// Returns an error if slice length is not valid for used buffer kind.
#[inline(always)]
pub fn try_new(buf: &[u8]) -> Result<Self, Error> {
let pos = buf.len();
if !Kind::invariant(pos, BlockSize::USIZE) {
return Err(Error);
}
let mut buffer = Block::<BlockSize>::default();
buffer[..pos].copy_from_slice(buf);
Ok(Self {
buffer,
pos: pos as u8,
_pd: PhantomData,
})
}
/// Digest data in `input` in blocks of size `BlockSize` using
/// the `compress` function, which accepts slice of blocks.
#[inline]
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);
}
/// Reset buffer by setting cursor position to zero.
#[inline(always)]
pub fn reset(&mut self) {
self.set_pos_unchecked(0);
}
/// Pad remaining data with zeros and return resulting block.
#[inline(always)]
pub fn pad_with_zeros(&mut self) -> &mut Block<BlockSize> {
let pos = self.get_pos();
self.buffer[pos..].iter_mut().for_each(|b| *b = 0);
self.set_pos_unchecked(0);
&mut self.buffer
}
/// 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
}
/// Return slice of data stored inside the buffer.
#[inline(always)]
pub fn get_data(&self) -> &[u8] {
&self.buffer[..self.get_pos()]
}
/// Set buffer content and cursor position.
///
/// # Panics
/// If `pos` is bigger or equal to block size.
#[inline]
pub fn set(&mut self, buf: Block<BlockSize>, pos: usize) {
assert!(Kind::invariant(pos, BlockSize::USIZE));
self.buffer = buf;
self.set_pos_unchecked(pos);
}
/// Return size of the internall buffer in bytes.
#[inline(always)]
pub fn size(&self) -> usize {
BlockSize::USIZE
}
/// Return number of remaining bytes in the internall buffer.
#[inline(always)]
pub fn remaining(&self) -> usize {
self.size() - self.get_pos()
}
#[inline(always)]
fn set_pos_unchecked(&mut self, pos: usize) {
debug_assert!(Kind::invariant(pos, BlockSize::USIZE));
self.pos = pos as u8;
}
}
impl<BlockSize> BlockBuffer<BlockSize, Eager>
where
BlockSize: ArrayLength<u8> + IsLess<U256>,
Le<BlockSize, U256>: NonZero,
{
/// Set `data` to generated blocks.
#[inline]
pub fn set_data(
&mut self,
mut data: &mut [u8],
mut process_blocks: impl FnMut(&mut [Block<BlockSize>]),
) {
let pos = self.get_pos();
let r = self.remaining();
let n = data.len();
if pos != 0 {
if n < r {
// double slicing allows to remove panic branches
data.copy_from_slice(&self.buffer[pos..][..n]);
self.set_pos_unchecked(pos + n);
return;
}
let (left, right) = data.split_at_mut(r);
data = right;
left.copy_from_slice(&self.buffer[pos..]);
}
let (blocks, leftover) = to_blocks_mut(data);
process_blocks(blocks);
let n = leftover.len();
if n != 0 {
let mut block = Default::default();
process_blocks(slice::from_mut(&mut block));
leftover.copy_from_slice(&block[..n]);
self.buffer = block;
}
self.set_pos_unchecked(n);
}
/// Compress remaining data after padding it with `delim`, zeros and
/// the `suffix` bytes. If there is not enough unused space, `compress`
/// will be called twice.
///
/// # Panics
/// If suffix length is bigger than block size.
#[inline(always)]
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);
}
}
/// Split message into mutable slice of parallel blocks, blocks, and leftover bytes.
#[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)
}
