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BLAKE3/src/lib.rs
Jack O'Connor 004b39a350 cargo fmt
2020-09-10 15:55:02 -04:00

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//! The official Rust implementation of the [BLAKE3] cryptographic hash
//! function.
//!
//! # Examples
//!
//! ```
//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
//! // Hash an input all at once.
//! let hash1 = blake3::hash(b"foobarbaz");
//!
//! // Hash an input incrementally.
//! let mut hasher = blake3::Hasher::new();
//! hasher.update(b"foo");
//! hasher.update(b"bar");
//! hasher.update(b"baz");
//! let hash2 = hasher.finalize();
//! assert_eq!(hash1, hash2);
//!
//! // Extended output. OutputReader also implements Read and Seek.
//! # #[cfg(feature = "std")] {
//! let mut output = [0; 1000];
//! let mut output_reader = hasher.finalize_xof();
//! output_reader.fill(&mut output);
//! assert_eq!(&output[..32], hash1.as_bytes());
//! # }
//!
//! // Print a hash as hex.
//! println!("{}", hash1.to_hex());
//! # Ok(())
//! # }
//! ```
//!
//! # Cargo Features
//!
//! The `rayon` feature provides [Rayon]-based multi-threading, in particular
//! the [`join::RayonJoin`] type for use with [`Hasher::update_with_join`]. It
//! is disabled by default, but enabled for [docs.rs].
//!
//! The `neon` feature enables ARM NEON support. Currently there is no runtime
//! CPU feature detection for NEON, so you must only enable this feature for
//! targets that are known to have NEON support. In particular, some ARMv7
//! targets support NEON, and some don't.
//!
//! The `std` feature (enabled by default) is required for implementations of
//! the [`Write`] and [`Seek`] traits, and also for runtime CPU feature
//! detection. If this feature is disabled, the only way to use the SIMD
//! implementations in this crate is to enable the corresponding instruction
//! sets statically for the entire build, with e.g. `RUSTFLAGS="-C
//! target-cpu=native"`. The resulting binary will not be portable to other
//! machines.
//!
//! [BLAKE3]: https://blake3.io
//! [Rayon]: https://github.com/rayon-rs/rayon
//! [`join::RayonJoin`]: join/enum.RayonJoin.html
//! [`Hasher::update_with_join`]: struct.Hasher.html#method.update_with_join
//! [docs.rs]: https://docs.rs/
//! [`Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
//! [`Seek`]: https://doc.rust-lang.org/std/io/trait.Seek.html
#![cfg_attr(not(feature = "std"), no_std)]
#[cfg(test)]
mod test;
// The guts module is for incremental use cases like the `bao` crate that need
// to explicitly compute chunk and parent chaining values. It is semi-stable
// and likely to keep working, but largely undocumented and not intended for
// widespread use.
#[doc(hidden)]
pub mod guts;
// The platform module is pub for benchmarks only. It is not stable.
#[doc(hidden)]
pub mod platform;
// Platform-specific implementations of the compression function. These
// BLAKE3-specific cfg flags are set in build.rs.
#[cfg(blake3_avx2_rust)]
#[path = "rust_avx2.rs"]
mod avx2;
#[cfg(blake3_avx2_ffi)]
#[path = "ffi_avx2.rs"]
mod avx2;
#[cfg(blake3_avx512_ffi)]
#[path = "ffi_avx512.rs"]
mod avx512;
#[cfg(feature = "neon")]
#[path = "ffi_neon.rs"]
mod neon;
mod portable;
#[cfg(blake3_sse2_rust)]
#[path = "rust_sse2.rs"]
mod sse2;
#[cfg(blake3_sse2_ffi)]
#[path = "ffi_sse2.rs"]
mod sse2;
#[cfg(blake3_sse41_rust)]
#[path = "rust_sse41.rs"]
mod sse41;
#[cfg(blake3_sse41_ffi)]
#[path = "ffi_sse41.rs"]
mod sse41;
pub mod traits;
pub mod join;
use arrayref::{array_mut_ref, array_ref};
use arrayvec::{ArrayString, ArrayVec};
use core::cmp;
use core::fmt;
use join::{Join, SerialJoin};
use platform::{Platform, MAX_SIMD_DEGREE, MAX_SIMD_DEGREE_OR_2};
/// The number of bytes in a [`Hash`](struct.Hash.html), 32.
pub const OUT_LEN: usize = 32;
/// The number of bytes in a key, 32.
pub const KEY_LEN: usize = 32;
// These constants are pub for incremental use cases like `bao`, as well as
// tests and benchmarks. Most callers should not need them.
#[doc(hidden)]
pub const BLOCK_LEN: usize = 64;
#[doc(hidden)]
pub const CHUNK_LEN: usize = 1024;
#[doc(hidden)]
pub const MAX_DEPTH: usize = 54; // 2^54 * CHUNK_LEN = 2^64
// While iterating the compression function within a chunk, the CV is
// represented as words, to avoid doing two extra endianness conversions for
// each compression in the portable implementation. But the hash_many interface
// needs to hash both input bytes and parent nodes, so its better for its
// output CVs to be represented as bytes.
type CVWords = [u32; 8];
type CVBytes = [u8; 32]; // little-endian
const IV: &CVWords = &[
0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19,
];
const MSG_SCHEDULE: [[usize; 16]; 7] = [
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
[2, 6, 3, 10, 7, 0, 4, 13, 1, 11, 12, 5, 9, 14, 15, 8],
[3, 4, 10, 12, 13, 2, 7, 14, 6, 5, 9, 0, 11, 15, 8, 1],
[10, 7, 12, 9, 14, 3, 13, 15, 4, 0, 11, 2, 5, 8, 1, 6],
[12, 13, 9, 11, 15, 10, 14, 8, 7, 2, 5, 3, 0, 1, 6, 4],
[9, 14, 11, 5, 8, 12, 15, 1, 13, 3, 0, 10, 2, 6, 4, 7],
[11, 15, 5, 0, 1, 9, 8, 6, 14, 10, 2, 12, 3, 4, 7, 13],
];
// These are the internal flags that we use to domain separate root/non-root,
// chunk/parent, and chunk beginning/middle/end. These get set at the high end
// of the block flags word in the compression function, so their values start
// high and go down.
const CHUNK_START: u8 = 1 << 0;
const CHUNK_END: u8 = 1 << 1;
const PARENT: u8 = 1 << 2;
const ROOT: u8 = 1 << 3;
const KEYED_HASH: u8 = 1 << 4;
const DERIVE_KEY_CONTEXT: u8 = 1 << 5;
const DERIVE_KEY_MATERIAL: u8 = 1 << 6;
#[inline]
fn counter_low(counter: u64) -> u32 {
counter as u32
}
#[inline]
fn counter_high(counter: u64) -> u32 {
(counter >> 32) as u32
}
/// An output of the default size, 32 bytes, which provides constant-time
/// equality checking.
///
/// `Hash` implements [`From`] and [`Into`] for `[u8; 32]`, and it provides an
/// explicit [`as_bytes`] method returning `&[u8; 32]`. However, byte arrays
/// and slices don't provide constant-time equality checking, which is often a
/// security requirement in software that handles private data. `Hash` doesn't
/// implement [`Deref`] or [`AsRef`], to avoid situations where a type
/// conversion happens implicitly and the constant-time property is
/// accidentally lost.
///
/// `Hash` provides the [`to_hex`] method for converting to hexadecimal. It
/// doesn't directly support converting from hexadecimal, but here's an example
/// of doing that with the [`hex`] crate:
///
/// ```
/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
/// use std::convert::TryInto;
///
/// let hash_hex = "d74981efa70a0c880b8d8c1985d075dbcbf679b99a5f9914e5aaf96b831a9e24";
/// let hash_bytes = hex::decode(hash_hex)?;
/// let hash_array: [u8; blake3::OUT_LEN] = hash_bytes[..].try_into()?;
/// let hash: blake3::Hash = hash_array.into();
/// # Ok(())
/// # }
/// ```
///
/// [`From`]: https://doc.rust-lang.org/std/convert/trait.From.html
/// [`Into`]: https://doc.rust-lang.org/std/convert/trait.Into.html
/// [`as_bytes`]: #method.as_bytes
/// [`Deref`]: https://doc.rust-lang.org/stable/std/ops/trait.Deref.html
/// [`AsRef`]: https://doc.rust-lang.org/std/convert/trait.AsRef.html
/// [`to_hex`]: #method.to_hex
/// [`hex`]: https://crates.io/crates/hex
#[derive(Clone, Copy, Hash)]
pub struct Hash([u8; OUT_LEN]);
impl Hash {
/// The bytes of the `Hash`. Note that byte arrays don't provide
/// constant-time equality checking, so if you need to compare hashes,
/// prefer the `Hash` type.
#[inline]
pub fn as_bytes(&self) -> &[u8; OUT_LEN] {
&self.0
}
/// The hexadecimal encoding of the `Hash`. The returned [`ArrayString`] is
/// a fixed size and doesn't allocate memory on the heap. Note that
/// [`ArrayString`] doesn't provide constant-time equality checking, so if
/// you need to compare hashes, prefer the `Hash` type.
///
/// [`ArrayString`]: https://docs.rs/arrayvec/0.5.1/arrayvec/struct.ArrayString.html
pub fn to_hex(&self) -> ArrayString<[u8; 2 * OUT_LEN]> {
let mut s = ArrayString::new();
let table = b"0123456789abcdef";
for &b in self.0.iter() {
s.push(table[(b >> 4) as usize] as char);
s.push(table[(b & 0xf) as usize] as char);
}
s
}
}
impl From<[u8; OUT_LEN]> for Hash {
#[inline]
fn from(bytes: [u8; OUT_LEN]) -> Self {
Self(bytes)
}
}
impl From<Hash> for [u8; OUT_LEN] {
#[inline]
fn from(hash: Hash) -> Self {
hash.0
}
}
/// This implementation is constant-time.
impl PartialEq for Hash {
#[inline]
fn eq(&self, other: &Hash) -> bool {
constant_time_eq::constant_time_eq_32(&self.0, &other.0)
}
}
/// This implementation is constant-time.
impl PartialEq<[u8; OUT_LEN]> for Hash {
#[inline]
fn eq(&self, other: &[u8; OUT_LEN]) -> bool {
constant_time_eq::constant_time_eq_32(&self.0, other)
}
}
impl Eq for Hash {}
impl fmt::Debug for Hash {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
// Formatting field as `&str` to reduce code size since the `Debug`
// dynamic dispatch table for `&str` is likely needed elsewhere already,
// but that for `ArrayString<[u8; 64]>` is not.
let hex = self.to_hex();
let hex: &str = hex.as_str();
f.debug_tuple("Hash").field(&hex).finish()
}
}
// Each chunk or parent node can produce either a 32-byte chaining value or, by
// setting the ROOT flag, any number of final output bytes. The Output struct
// captures the state just prior to choosing between those two possibilities.
#[derive(Clone)]
struct Output {
input_chaining_value: CVWords,
block: [u8; 64],
block_len: u8,
counter: u64,
flags: u8,
platform: Platform,
}
impl Output {
fn chaining_value(&self) -> CVBytes {
let mut cv = self.input_chaining_value;
self.platform.compress_in_place(
&mut cv,
&self.block,
self.block_len,
self.counter,
self.flags,
);
platform::le_bytes_from_words_32(&cv)
}
fn root_hash(&self) -> Hash {
debug_assert_eq!(self.counter, 0);
let mut cv = self.input_chaining_value;
self.platform
.compress_in_place(&mut cv, &self.block, self.block_len, 0, self.flags | ROOT);
Hash(platform::le_bytes_from_words_32(&cv))
}
fn root_output_block(&self) -> [u8; 2 * OUT_LEN] {
self.platform.compress_xof(
&self.input_chaining_value,
&self.block,
self.block_len,
self.counter,
self.flags | ROOT,
)
}
}
#[derive(Clone)]
struct ChunkState {
cv: CVWords,
chunk_counter: u64,
buf: [u8; BLOCK_LEN],
buf_len: u8,
blocks_compressed: u8,
flags: u8,
platform: Platform,
}
impl ChunkState {
fn new(key: &CVWords, chunk_counter: u64, flags: u8, platform: Platform) -> Self {
Self {
cv: *key,
chunk_counter,
buf: [0; BLOCK_LEN],
buf_len: 0,
blocks_compressed: 0,
flags,
platform,
}
}
fn len(&self) -> usize {
BLOCK_LEN * self.blocks_compressed as usize + self.buf_len as usize
}
fn fill_buf(&mut self, input: &mut &[u8]) {
let want = BLOCK_LEN - self.buf_len as usize;
let take = cmp::min(want, input.len());
self.buf[self.buf_len as usize..][..take].copy_from_slice(&input[..take]);
self.buf_len += take as u8;
*input = &input[take..];
}
fn start_flag(&self) -> u8 {
if self.blocks_compressed == 0 {
CHUNK_START
} else {
0
}
}
// Try to avoid buffering as much as possible, by compressing directly from
// the input slice when full blocks are available.
fn update(&mut self, mut input: &[u8]) -> &mut Self {
if self.buf_len > 0 {
self.fill_buf(&mut input);
if !input.is_empty() {
debug_assert_eq!(self.buf_len as usize, BLOCK_LEN);
let block_flags = self.flags | self.start_flag(); // borrowck
self.platform.compress_in_place(
&mut self.cv,
&self.buf,
BLOCK_LEN as u8,
self.chunk_counter,
block_flags,
);
self.buf_len = 0;
self.buf = [0; BLOCK_LEN];
self.blocks_compressed += 1;
}
}
while input.len() > BLOCK_LEN {
debug_assert_eq!(self.buf_len, 0);
let block_flags = self.flags | self.start_flag(); // borrowck
self.platform.compress_in_place(
&mut self.cv,
array_ref!(input, 0, BLOCK_LEN),
BLOCK_LEN as u8,
self.chunk_counter,
block_flags,
);
self.blocks_compressed += 1;
input = &input[BLOCK_LEN..];
}
self.fill_buf(&mut input);
debug_assert!(input.is_empty());
debug_assert!(self.len() <= CHUNK_LEN);
self
}
fn output(&self) -> Output {
let block_flags = self.flags | self.start_flag() | CHUNK_END;
Output {
input_chaining_value: self.cv,
block: self.buf,
block_len: self.buf_len,
counter: self.chunk_counter,
flags: block_flags,
platform: self.platform,
}
}
}
// Don't derive(Debug), because the state may be secret.
impl fmt::Debug for ChunkState {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("ChunkState")
.field("len", &self.len())
.field("chunk_counter", &self.chunk_counter)
.field("flags", &self.flags)
.field("platform", &self.platform)
.finish()
}
}
// IMPLEMENTATION NOTE
// ===================
// The recursive function compress_subtree_wide(), implemented below, is the
// basis of high-performance BLAKE3. We use it both for all-at-once hashing,
// and for the incremental input with Hasher (though we have to be careful with
// subtree boundaries in the incremental case). compress_subtree_wide() applies
// several optimizations at the same time:
// - Multi-threading with Rayon.
// - Parallel chunk hashing with SIMD.
// - Parallel parent hashing with SIMD. Note that while SIMD chunk hashing
// maxes out at MAX_SIMD_DEGREE*CHUNK_LEN, parallel parent hashing continues
// to benefit from larger inputs, because more levels of the tree benefit can
// use full-width SIMD vectors for parent hashing. Without parallel parent
// hashing, we lose about 10% of overall throughput on AVX2 and AVX-512.
// pub for benchmarks
#[doc(hidden)]
#[derive(Clone, Copy)]
pub enum IncrementCounter {
Yes,
No,
}
impl IncrementCounter {
#[inline]
fn yes(&self) -> bool {
match self {
IncrementCounter::Yes => true,
IncrementCounter::No => false,
}
}
}
// The largest power of two less than or equal to `n`, used for left_len()
// immediately below, and also directly in Hasher::update().
fn largest_power_of_two_leq(n: usize) -> usize {
((n / 2) + 1).next_power_of_two()
}
// Given some input larger than one chunk, return the number of bytes that
// should go in the left subtree. This is the largest power-of-2 number of
// chunks that leaves at least 1 byte for the right subtree.
fn left_len(content_len: usize) -> usize {
debug_assert!(content_len > CHUNK_LEN);
// Subtract 1 to reserve at least one byte for the right side.
let full_chunks = (content_len - 1) / CHUNK_LEN;
largest_power_of_two_leq(full_chunks) * CHUNK_LEN
}
// Use SIMD parallelism to hash up to MAX_SIMD_DEGREE chunks at the same time
// on a single thread. Write out the chunk chaining values and return the
// number of chunks hashed. These chunks are never the root and never empty;
// those cases use a different codepath.
fn compress_chunks_parallel(
input: &[u8],
key: &CVWords,
chunk_counter: u64,
flags: u8,
platform: Platform,
out: &mut [u8],
) -> usize {
debug_assert!(!input.is_empty(), "empty chunks below the root");
debug_assert!(input.len() <= MAX_SIMD_DEGREE * CHUNK_LEN);
let mut chunks_exact = input.chunks_exact(CHUNK_LEN);
let mut chunks_array = ArrayVec::<[&[u8; CHUNK_LEN]; MAX_SIMD_DEGREE]>::new();
for chunk in &mut chunks_exact {
chunks_array.push(array_ref!(chunk, 0, CHUNK_LEN));
}
platform.hash_many(
&chunks_array,
key,
chunk_counter,
IncrementCounter::Yes,
flags,
CHUNK_START,
CHUNK_END,
out,
);
// Hash the remaining partial chunk, if there is one. Note that the empty
// chunk (meaning the empty message) is a different codepath.
let chunks_so_far = chunks_array.len();
if !chunks_exact.remainder().is_empty() {
let counter = chunk_counter + chunks_so_far as u64;
let mut chunk_state = ChunkState::new(key, counter, flags, platform);
chunk_state.update(chunks_exact.remainder());
*array_mut_ref!(out, chunks_so_far * OUT_LEN, OUT_LEN) =
chunk_state.output().chaining_value();
chunks_so_far + 1
} else {
chunks_so_far
}
}
// Use SIMD parallelism to hash up to MAX_SIMD_DEGREE parents at the same time
// on a single thread. Write out the parent chaining values and return the
// number of parents hashed. (If there's an odd input chaining value left over,
// return it as an additional output.) These parents are never the root and
// never empty; those cases use a different codepath.
fn compress_parents_parallel(
child_chaining_values: &[u8],
key: &CVWords,
flags: u8,
platform: Platform,
out: &mut [u8],
) -> usize {
debug_assert_eq!(child_chaining_values.len() % OUT_LEN, 0, "wacky hash bytes");
let num_children = child_chaining_values.len() / OUT_LEN;
debug_assert!(num_children >= 2, "not enough children");
debug_assert!(num_children <= 2 * MAX_SIMD_DEGREE_OR_2, "too many");
let mut parents_exact = child_chaining_values.chunks_exact(BLOCK_LEN);
// Use MAX_SIMD_DEGREE_OR_2 rather than MAX_SIMD_DEGREE here, because of
// the requirements of compress_subtree_wide().
let mut parents_array = ArrayVec::<[&[u8; BLOCK_LEN]; MAX_SIMD_DEGREE_OR_2]>::new();
for parent in &mut parents_exact {
parents_array.push(array_ref!(parent, 0, BLOCK_LEN));
}
platform.hash_many(
&parents_array,
key,
0, // Parents always use counter 0.
IncrementCounter::No,
flags | PARENT,
0, // Parents have no start flags.
0, // Parents have no end flags.
out,
);
// If there's an odd child left over, it becomes an output.
let parents_so_far = parents_array.len();
if !parents_exact.remainder().is_empty() {
out[parents_so_far * OUT_LEN..][..OUT_LEN].copy_from_slice(parents_exact.remainder());
parents_so_far + 1
} else {
parents_so_far
}
}
// The wide helper function returns (writes out) an array of chaining values
// and returns the length of that array. The number of chaining values returned
// is the dyanmically detected SIMD degree, at most MAX_SIMD_DEGREE. Or fewer,
// if the input is shorter than that many chunks. The reason for maintaining a
// wide array of chaining values going back up the tree, is to allow the
// implementation to hash as many parents in parallel as possible.
//
// As a special case when the SIMD degree is 1, this function will still return
// at least 2 outputs. This guarantees that this function doesn't perform the
// root compression. (If it did, it would use the wrong flags, and also we
// wouldn't be able to implement exendable ouput.) Note that this function is
// not used when the whole input is only 1 chunk long; that's a different
// codepath.
//
// Why not just have the caller split the input on the first update(), instead
// of implementing this special rule? Because we don't want to limit SIMD or
// multi-threading parallelism for that update().
fn compress_subtree_wide<J: Join>(
input: &[u8],
key: &CVWords,
chunk_counter: u64,
flags: u8,
platform: Platform,
out: &mut [u8],
) -> usize {
// Note that the single chunk case does *not* bump the SIMD degree up to 2
// when it is 1. This allows Rayon the option of multi-threading even the
// 2-chunk case, which can help performance on smaller platforms.
if input.len() <= platform.simd_degree() * CHUNK_LEN {
return compress_chunks_parallel(input, key, chunk_counter, flags, platform, out);
}
// With more than simd_degree chunks, we need to recurse. Start by dividing
// the input into left and right subtrees. (Note that this is only optimal
// as long as the SIMD degree is a power of 2. If we ever get a SIMD degree
// of 3 or something, we'll need a more complicated strategy.)
debug_assert_eq!(platform.simd_degree().count_ones(), 1, "power of 2");
let (left, right) = input.split_at(left_len(input.len()));
let right_chunk_counter = chunk_counter + (left.len() / CHUNK_LEN) as u64;
// Make space for the child outputs. Here we use MAX_SIMD_DEGREE_OR_2 to
// account for the special case of returning 2 outputs when the SIMD degree
// is 1.
let mut cv_array = [0; 2 * MAX_SIMD_DEGREE_OR_2 * OUT_LEN];
let degree = if left.len() == CHUNK_LEN {
// The "simd_degree=1 and we're at the leaf nodes" case.
debug_assert_eq!(platform.simd_degree(), 1);
1
} else {
cmp::max(platform.simd_degree(), 2)
};
let (left_out, right_out) = cv_array.split_at_mut(degree * OUT_LEN);
// Recurse! This uses multiple threads if the "rayon" feature is enabled.
let (left_n, right_n) = J::join(
|| compress_subtree_wide::<J>(left, key, chunk_counter, flags, platform, left_out),
|| compress_subtree_wide::<J>(right, key, right_chunk_counter, flags, platform, right_out),
left.len(),
right.len(),
);
// The special case again. If simd_degree=1, then we'll have left_n=1 and
// right_n=1. Rather than compressing them into a single output, return
// them directly, to make sure we always have at least two outputs.
debug_assert_eq!(left_n, degree);
debug_assert!(right_n >= 1 && right_n <= left_n);
if left_n == 1 {
out[..2 * OUT_LEN].copy_from_slice(&cv_array[..2 * OUT_LEN]);
return 2;
}
// Otherwise, do one layer of parent node compression.
let num_children = left_n + right_n;
compress_parents_parallel(
&cv_array[..num_children * OUT_LEN],
key,
flags,
platform,
out,
)
}
// Hash a subtree with compress_subtree_wide(), and then condense the resulting
// list of chaining values down to a single parent node. Don't compress that
// last parent node, however. Instead, return its message bytes (the
// concatenated chaining values of its children). This is necessary when the
// first call to update() supplies a complete subtree, because the topmost
// parent node of that subtree could end up being the root. It's also necessary
// for extended output in the general case.
//
// As with compress_subtree_wide(), this function is not used on inputs of 1
// chunk or less. That's a different codepath.
fn compress_subtree_to_parent_node<J: Join>(
input: &[u8],
key: &CVWords,
chunk_counter: u64,
flags: u8,
platform: Platform,
) -> [u8; BLOCK_LEN] {
debug_assert!(input.len() > CHUNK_LEN);
let mut cv_array = [0; MAX_SIMD_DEGREE_OR_2 * OUT_LEN];
let mut num_cvs =
compress_subtree_wide::<J>(input, &key, chunk_counter, flags, platform, &mut cv_array);
debug_assert!(num_cvs >= 2);
// If MAX_SIMD_DEGREE is greater than 2 and there's enough input,
// compress_subtree_wide() returns more than 2 chaining values. Condense
// them into 2 by forming parent nodes repeatedly.
let mut out_array = [0; MAX_SIMD_DEGREE_OR_2 * OUT_LEN / 2];
while num_cvs > 2 {
let cv_slice = &cv_array[..num_cvs * OUT_LEN];
num_cvs = compress_parents_parallel(cv_slice, key, flags, platform, &mut out_array);
cv_array[..num_cvs * OUT_LEN].copy_from_slice(&out_array[..num_cvs * OUT_LEN]);
}
*array_ref!(cv_array, 0, 2 * OUT_LEN)
}
// Hash a complete input all at once. Unlike compress_subtree_wide() and
// compress_subtree_to_parent_node(), this function handles the 1 chunk case.
// Note that this we use SerialJoin here, so this is always single-threaded.
fn hash_all_at_once(input: &[u8], key: &CVWords, flags: u8) -> Output {
let platform = Platform::detect();
// If the whole subtree is one chunk, hash it directly with a ChunkState.
if input.len() <= CHUNK_LEN {
return ChunkState::new(key, 0, flags, platform)
.update(input)
.output();
}
// Otherwise construct an Output object from the parent node returned by
// compress_subtree_to_parent_node().
Output {
input_chaining_value: *key,
block: compress_subtree_to_parent_node::<SerialJoin>(input, key, 0, flags, platform),
block_len: BLOCK_LEN as u8,
counter: 0,
flags: flags | PARENT,
platform,
}
}
/// The default hash function.
///
/// For an incremental version that accepts multiple writes, see [`Hasher::update`].
///
/// This function is always single-threaded. For multi-threading support, see
/// [`Hasher::update_with_join`].
///
/// [`Hasher::update`]: struct.Hasher.html#method.update
/// [`Hasher::update_with_join`]: struct.Hasher.html#method.update_with_join
pub fn hash(input: &[u8]) -> Hash {
hash_all_at_once(input, IV, 0).root_hash()
}
/// The keyed hash function.
///
/// This is suitable for use as a message authentication code, for
/// example to replace an HMAC instance.
/// In that use case, the constant-time equality checking provided by
/// [`Hash`](struct.Hash.html) is almost always a security requirement, and
/// callers need to be careful not to compare MACs as raw bytes.
///
/// This function is always single-threaded. For multi-threading support, see
/// [`Hasher::update_with_join`].
///
/// [`Hasher::update_with_join`]: struct.Hasher.html#method.update_with_join
pub fn keyed_hash(key: &[u8; KEY_LEN], input: &[u8]) -> Hash {
let key_words = platform::words_from_le_bytes_32(key);
hash_all_at_once(input, &key_words, KEYED_HASH).root_hash()
}
/// The key derivation function.
///
/// Given cryptographic key material of any length and a context string of any
/// length, this function outputs a derived subkey of any length. **The context
/// string should be hardcoded, globally unique, and application-specific.** A
/// good default format for such strings is `"[application] [commit timestamp]
/// [purpose]"`, e.g., `"example.com 2019-12-25 16:18:03 session tokens v1"`.
///
/// Key derivation is important when you want to use the same key in multiple
/// algorithms or use cases. Using the same key with different cryptographic
/// algorithms is generally forbidden, and deriving a separate subkey for each
/// use case protects you from bad interactions. Derived keys also mitigate the
/// damage from one part of your application accidentally leaking its key.
///
/// As a rare exception to that general rule, however, it is possible to use
/// `derive_key` itself with key material that you are already using with
/// another algorithm. You might need to do this if you're adding features to
/// an existing application, which does not yet use key derivation internally.
/// However, you still must not share key material with algorithms that forbid
/// key reuse entirely, like a one-time pad.
///
/// Note that BLAKE3 is not a password hash, and **`derive_key` should never be
/// used with passwords.** Instead, use a dedicated password hash like
/// [Argon2]. Password hashes are entirely different from generic hash
/// functions, with opposite design requirements.
///
/// This function is always single-threaded. For multi-threading support, see
/// [`Hasher::update_with_join`].
///
/// [`Hasher::new_derive_key`]: struct.Hasher.html#method.new_derive_key
/// [`Hasher::finalize_xof`]: struct.Hasher.html#method.finalize_xof
/// [Argon2]: https://en.wikipedia.org/wiki/Argon2
/// [`Hasher::update_with_join`]: struct.Hasher.html#method.update_with_join
pub fn derive_key(context: &str, key_material: &[u8], output: &mut [u8]) {
let context_key = hash_all_at_once(context.as_bytes(), IV, DERIVE_KEY_CONTEXT).root_hash();
let context_key_words = platform::words_from_le_bytes_32(context_key.as_bytes());
let inner_output = hash_all_at_once(key_material, &context_key_words, DERIVE_KEY_MATERIAL);
OutputReader::new(inner_output).fill(output);
}
fn parent_node_output(
left_child: &CVBytes,
right_child: &CVBytes,
key: &CVWords,
flags: u8,
platform: Platform,
) -> Output {
let mut block = [0; BLOCK_LEN];
block[..32].copy_from_slice(left_child);
block[32..].copy_from_slice(right_child);
Output {
input_chaining_value: *key,
block,
block_len: BLOCK_LEN as u8,
counter: 0,
flags: flags | PARENT,
platform,
}
}
/// An incremental hash state that can accept any number of writes.
///
/// In addition to its inherent methods, this type implements several commonly
/// used traits from the [`digest`](https://crates.io/crates/digest) and
/// [`crypto_mac`](https://crates.io/crates/crypto-mac) crates.
///
/// **Performance note:** The [`update`] and [`update_with_join`] methods
/// perform poorly when the caller's input buffer is small. See their method
/// docs below. A 16 KiB buffer is large enough to leverage all currently
/// supported SIMD instruction sets.
///
/// # Examples
///
/// ```
/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
/// // Hash an input incrementally.
/// let mut hasher = blake3::Hasher::new();
/// hasher.update(b"foo");
/// hasher.update(b"bar");
/// hasher.update(b"baz");
/// assert_eq!(hasher.finalize(), blake3::hash(b"foobarbaz"));
///
/// // Extended output. OutputReader also implements Read and Seek.
/// # #[cfg(feature = "std")] {
/// let mut output = [0; 1000];
/// let mut output_reader = hasher.finalize_xof();
/// output_reader.fill(&mut output);
/// assert_eq!(&output[..32], blake3::hash(b"foobarbaz").as_bytes());
/// # }
/// # Ok(())
/// # }
/// ```
///
/// [`update`]: #method.update
/// [`update_with_join`]: #method.update_with_join
#[derive(Clone)]
pub struct Hasher {
key: CVWords,
chunk_state: ChunkState,
// The stack size is MAX_DEPTH + 1 because we do lazy merging. For example,
// with 7 chunks, we have 3 entries in the stack. Adding an 8th chunk
// requires a 4th entry, rather than merging everything down to 1, because
// we don't know whether more input is coming. This is different from how
// the reference implementation does things.
cv_stack: ArrayVec<[CVBytes; MAX_DEPTH + 1]>,
}
impl Hasher {
fn new_internal(key: &CVWords, flags: u8) -> Self {
Self {
key: *key,
chunk_state: ChunkState::new(key, 0, flags, Platform::detect()),
cv_stack: ArrayVec::new(),
}
}
/// Construct a new `Hasher` for the regular hash function.
pub fn new() -> Self {
Self::new_internal(IV, 0)
}
/// Construct a new `Hasher` for the keyed hash function. See
/// [`keyed_hash`].
///
/// [`keyed_hash`]: fn.keyed_hash.html
pub fn new_keyed(key: &[u8; KEY_LEN]) -> Self {
let key_words = platform::words_from_le_bytes_32(key);
Self::new_internal(&key_words, KEYED_HASH)
}
/// Construct a new `Hasher` for the key derivation function. See
/// [`derive_key`]. The context string should be hardcoded, globally
/// unique, and application-specific.
///
/// [`derive_key`]: fn.derive_key.html
pub fn new_derive_key(context: &str) -> Self {
let context_key = hash_all_at_once(context.as_bytes(), IV, DERIVE_KEY_CONTEXT).root_hash();
let context_key_words = platform::words_from_le_bytes_32(context_key.as_bytes());
Self::new_internal(&context_key_words, DERIVE_KEY_MATERIAL)
}
/// Reset the `Hasher` to its initial state.
///
/// This is functionally the same as overwriting the `Hasher` with a new
/// one, using the same key or context string if any. However, depending on
/// how much inlining the optimizer does, moving a `Hasher` might copy its
/// entire CV stack, most of which is useless uninitialized bytes. This
/// methods avoids that copy.
pub fn reset(&mut self) -> &mut Self {
self.chunk_state = ChunkState::new(
&self.key,
0,
self.chunk_state.flags,
self.chunk_state.platform,
);
self.cv_stack.clear();
self
}
// As described in push_cv() below, we do "lazy merging", delaying merges
// until right before the next CV is about to be added. This is different
// from the reference implementation. Another difference is that we aren't
// always merging 1 chunk at a time. Instead, each CV might represent any
// power-of-two number of chunks, as long as the smaller-above-larger stack
// order is maintained. Instead of the "count the trailing 0-bits"
// algorithm described in the spec, we use a "count the total number of
// 1-bits" variant that doesn't require us to retain the subtree size of
// the CV on top of the stack. The principle is the same: each CV that
// should remain in the stack is represented by a 1-bit in the total number
// of chunks (or bytes) so far.
fn merge_cv_stack(&mut self, total_len: u64) {
let post_merge_stack_len = total_len.count_ones() as usize;
while self.cv_stack.len() > post_merge_stack_len {
let right_child = self.cv_stack.pop().unwrap();
let left_child = self.cv_stack.pop().unwrap();
let parent_output = parent_node_output(
&left_child,
&right_child,
&self.key,
self.chunk_state.flags,
self.chunk_state.platform,
);
self.cv_stack.push(parent_output.chaining_value());
}
}
// In reference_impl.rs, we merge the new CV with existing CVs from the
// stack before pushing it. We can do that because we know more input is
// coming, so we know none of the merges are root.
//
// This setting is different. We want to feed as much input as possible to
// compress_subtree_wide(), without setting aside anything for the
// chunk_state. If the user gives us 64 KiB, we want to parallelize over
// all 64 KiB at once as a single subtree, if at all possible.
//
// This leads to two problems:
// 1) This 64 KiB input might be the only call that ever gets made to
// update. In this case, the root node of the 64 KiB subtree would be
// the root node of the whole tree, and it would need to be ROOT
// finalized. We can't compress it until we know.
// 2) This 64 KiB input might complete a larger tree, whose root node is
// similarly going to be the the root of the whole tree. For example,
// maybe we have 196 KiB (that is, 128 + 64) hashed so far. We can't
// compress the node at the root of the 256 KiB subtree until we know
// how to finalize it.
//
// The second problem is solved with "lazy merging". That is, when we're
// about to add a CV to the stack, we don't merge it with anything first,
// as the reference impl does. Instead we do merges using the *previous* CV
// that was added, which is sitting on top of the stack, and we put the new
// CV (unmerged) on top of the stack afterwards. This guarantees that we
// never merge the root node until finalize().
//
// Solving the first problem requires an additional tool,
// compress_subtree_to_parent_node(). That function always returns the top
// *two* chaining values of the subtree it's compressing. We then do lazy
// merging with each of them separately, so that the second CV will always
// remain unmerged. (That also helps us support extendable output when
// we're hashing an input all-at-once.)
fn push_cv(&mut self, new_cv: &CVBytes, chunk_counter: u64) {
self.merge_cv_stack(chunk_counter);
self.cv_stack.push(*new_cv);
}
/// Add input bytes to the hash state. You can call this any number of
/// times.
///
/// This method is always single-threaded. For multi-threading support, see
/// `update_with_join` below.
///
/// Note that the degree of SIMD parallelism that `update` can use is
/// limited by the size of this input buffer. The 8 KiB buffer currently
/// used by [`std::io::copy`] is enough to leverage AVX2, for example, but
/// not enough to leverage AVX-512. A 16 KiB buffer is large enough to
/// leverage all currently supported SIMD instruction sets.
///
/// [`std::io::copy`]: https://doc.rust-lang.org/std/io/fn.copy.html
pub fn update(&mut self, input: &[u8]) -> &mut Self {
self.update_with_join::<SerialJoin>(input)
}
/// Add input bytes to the hash state, as with `update`, but potentially
/// using multi-threading. See the example below, and the
/// [`join`](join/index.html) module for a more detailed explanation.
///
/// To get any performance benefit from multi-threading, the input buffer
/// size needs to be very large. As a rule of thumb on x86_64, there is no
/// benefit to multi-threading inputs less than 128 KiB. Other platforms
/// have different thresholds, and in general you need to benchmark your
/// specific use case. Where possible, memory mapping an entire input file
/// is recommended, to take maximum advantage of multi-threading without
/// needing to tune a specific buffer size. Where memory mapping is not
/// possible, good multi-threading performance requires doing IO on a
/// background thread, to avoid sleeping all your worker threads while the
/// input buffer is (serially) refilled. This is quite complicated compared
/// to memory mapping.
///
/// # Example
///
/// ```
/// // Hash a large input using multi-threading. Note that multi-threading
/// // comes with some overhead, and it can actually hurt performance for small
/// // inputs. The meaning of "small" varies, however, depending on the
/// // platform and the number of threads. (On x86_64, the cutoff tends to be
/// // around 128 KiB.) You should benchmark your own use case to see whether
/// // multi-threading helps.
/// # #[cfg(feature = "rayon")]
/// # {
/// # fn some_large_input() -> &'static [u8] { b"foo" }
/// let input: &[u8] = some_large_input();
/// let mut hasher = blake3::Hasher::new();
/// hasher.update_with_join::<blake3::join::RayonJoin>(input);
/// let hash = hasher.finalize();
/// # }
/// ```
pub fn update_with_join<J: Join>(&mut self, mut input: &[u8]) -> &mut Self {
// If we have some partial chunk bytes in the internal chunk_state, we
// need to finish that chunk first.
if self.chunk_state.len() > 0 {
let want = CHUNK_LEN - self.chunk_state.len();
let take = cmp::min(want, input.len());
self.chunk_state.update(&input[..take]);
input = &input[take..];
if !input.is_empty() {
// We've filled the current chunk, and there's more input
// coming, so we know it's not the root and we can finalize it.
// Then we'll proceed to hashing whole chunks below.
debug_assert_eq!(self.chunk_state.len(), CHUNK_LEN);
let chunk_cv = self.chunk_state.output().chaining_value();
self.push_cv(&chunk_cv, self.chunk_state.chunk_counter);
self.chunk_state = ChunkState::new(
&self.key,
self.chunk_state.chunk_counter + 1,
self.chunk_state.flags,
self.chunk_state.platform,
);
} else {
return self;
}
}
// Now the chunk_state is clear, and we have more input. If there's
// more than a single chunk (so, definitely not the root chunk), hash
// the largest whole subtree we can, with the full benefits of SIMD and
// multi-threading parallelism. Two restrictions:
// - The subtree has to be a power-of-2 number of chunks. Only subtrees
// along the right edge can be incomplete, and we don't know where
// the right edge is going to be until we get to finalize().
// - The subtree must evenly divide the total number of chunks up until
// this point (if total is not 0). If the current incomplete subtree
// is only waiting for 1 more chunk, we can't hash a subtree of 4
// chunks. We have to complete the current subtree first.
// Because we might need to break up the input to form powers of 2, or
// to evenly divide what we already have, this part runs in a loop.
while input.len() > CHUNK_LEN {
debug_assert_eq!(self.chunk_state.len(), 0, "no partial chunk data");
debug_assert_eq!(CHUNK_LEN.count_ones(), 1, "power of 2 chunk len");
let mut subtree_len = largest_power_of_two_leq(input.len());
let count_so_far = self.chunk_state.chunk_counter * CHUNK_LEN as u64;
// Shrink the subtree_len until it evenly divides the count so far.
// We know that subtree_len itself is a power of 2, so we can use a
// bitmasking trick instead of an actual remainder operation. (Note
// that if the caller consistently passes power-of-2 inputs of the
// same size, as is hopefully typical, this loop condition will
// always fail, and subtree_len will always be the full length of
// the input.)
//
// An aside: We don't have to shrink subtree_len quite this much.
// For example, if count_so_far is 1, we could pass 2 chunks to
// compress_subtree_to_parent_node. Since we'll get 2 CVs back,
// we'll still get the right answer in the end, and we might get to
// use 2-way SIMD parallelism. The problem with this optimization,
// is that it gets us stuck always hashing 2 chunks. The total
// number of chunks will remain odd, and we'll never graduate to
// higher degrees of parallelism. See
// https://github.com/BLAKE3-team/BLAKE3/issues/69.
while (subtree_len - 1) as u64 & count_so_far != 0 {
subtree_len /= 2;
}
// The shrunken subtree_len might now be 1 chunk long. If so, hash
// that one chunk by itself. Otherwise, compress the subtree into a
// pair of CVs.
let subtree_chunks = (subtree_len / CHUNK_LEN) as u64;
if subtree_len <= CHUNK_LEN {
debug_assert_eq!(subtree_len, CHUNK_LEN);
self.push_cv(
&ChunkState::new(
&self.key,
self.chunk_state.chunk_counter,
self.chunk_state.flags,
self.chunk_state.platform,
)
.update(&input[..subtree_len])
.output()
.chaining_value(),
self.chunk_state.chunk_counter,
);
} else {
// This is the high-performance happy path, though getting here
// depends on the caller giving us a long enough input.
let cv_pair = compress_subtree_to_parent_node::<J>(
&input[..subtree_len],
&self.key,
self.chunk_state.chunk_counter,
self.chunk_state.flags,
self.chunk_state.platform,
);
let left_cv = array_ref!(cv_pair, 0, 32);
let right_cv = array_ref!(cv_pair, 32, 32);
// Push the two CVs we received into the CV stack in order. Because
// the stack merges lazily, this guarantees we aren't merging the
// root.
self.push_cv(left_cv, self.chunk_state.chunk_counter);
self.push_cv(
right_cv,
self.chunk_state.chunk_counter + (subtree_chunks / 2),
);
}
self.chunk_state.chunk_counter += subtree_chunks;
input = &input[subtree_len..];
}
// What remains is 1 chunk or less. Add it to the chunk state.
debug_assert!(input.len() <= CHUNK_LEN);
if !input.is_empty() {
self.chunk_state.update(input);
// Having added some input to the chunk_state, we know what's in
// the CV stack won't become the root node, and we can do an extra
// merge. This simplifies finalize().
self.merge_cv_stack(self.chunk_state.chunk_counter);
}
self
}
fn final_output(&self) -> Output {
// If the current chunk is the only chunk, that makes it the root node
// also. Convert it directly into an Output. Otherwise, we need to
// merge subtrees below.
if self.cv_stack.is_empty() {
debug_assert_eq!(self.chunk_state.chunk_counter, 0);
return self.chunk_state.output();
}
// If there are any bytes in the ChunkState, finalize that chunk and
// merge its CV with everything in the CV stack. In that case, the work
// we did at the end of update() above guarantees that the stack
// doesn't contain any unmerged subtrees that need to be merged first.
// (This is important, because if there were two chunk hashes sitting
// on top of the stack, they would need to merge with each other, and
// merging a new chunk hash into them would be incorrect.)
//
// If there are no bytes in the ChunkState, we'll merge what's already
// in the stack. In this case it's fine if there are unmerged chunks on
// top, because we'll merge them with each other. Note that the case of
// the empty chunk is taken care of above.
let mut output: Output;
let mut num_cvs_remaining = self.cv_stack.len();
if self.chunk_state.len() > 0 {
debug_assert_eq!(
self.cv_stack.len(),
self.chunk_state.chunk_counter.count_ones() as usize,
"cv stack does not need a merge"
);
output = self.chunk_state.output();
} else {
debug_assert!(self.cv_stack.len() >= 2);
output = parent_node_output(
&self.cv_stack[num_cvs_remaining - 2],
&self.cv_stack[num_cvs_remaining - 1],
&self.key,
self.chunk_state.flags,
self.chunk_state.platform,
);
num_cvs_remaining -= 2;
}
while num_cvs_remaining > 0 {
output = parent_node_output(
&self.cv_stack[num_cvs_remaining - 1],
&output.chaining_value(),
&self.key,
self.chunk_state.flags,
self.chunk_state.platform,
);
num_cvs_remaining -= 1;
}
output
}
/// Finalize the hash state and return the [`Hash`](struct.Hash.html) of
/// the input.
///
/// This method is idempotent. Calling it twice will give the same result.
/// You can also add more input and finalize again.
pub fn finalize(&self) -> Hash {
self.final_output().root_hash()
}
/// Finalize the hash state and return an [`OutputReader`], which can
/// supply any number of output bytes.
///
/// This method is idempotent. Calling it twice will give the same result.
/// You can also add more input and finalize again.
///
/// [`OutputReader`]: struct.OutputReader.html
pub fn finalize_xof(&self) -> OutputReader {
OutputReader::new(self.final_output())
}
}
// Don't derive(Debug), because the state may be secret.
impl fmt::Debug for Hasher {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Hasher")
.field("flags", &self.chunk_state.flags)
.field("platform", &self.chunk_state.platform)
.finish()
}
}
impl Default for Hasher {
#[inline]
fn default() -> Self {
Self::new()
}
}
#[cfg(feature = "std")]
impl std::io::Write for Hasher {
/// This is equivalent to [`update`](#method.update).
#[inline]
fn write(&mut self, input: &[u8]) -> std::io::Result<usize> {
self.update(input);
Ok(input.len())
}
#[inline]
fn flush(&mut self) -> std::io::Result<()> {
Ok(())
}
}
/// An incremental reader for extended output, returned by
/// [`Hasher::finalize_xof`](struct.Hasher.html#method.finalize_xof).
#[derive(Clone)]
pub struct OutputReader {
inner: Output,
position_within_block: u8,
}
impl OutputReader {
fn new(inner: Output) -> Self {
Self {
inner,
position_within_block: 0,
}
}
/// Fill a buffer with output bytes and advance the position of the
/// `OutputReader`. This is equivalent to [`Read::read`], except that it
/// doesn't return a `Result`. Both methods always fill the entire buffer.
///
/// Note that `OutputReader` doesn't buffer output bytes internally, so
/// calling `fill` repeatedly with a short-length or odd-length slice will
/// end up performing the same compression multiple times. If you're
/// reading output in a loop, prefer a slice length that's a multiple of
/// 64.
///
/// The maximum output size of BLAKE3 is 2<sup>64</sup>-1 bytes. If you try
/// to extract more than that, for example by seeking near the end and
/// reading further, the behavior is unspecified.
///
/// [`Read::read`]: #method.read
pub fn fill(&mut self, mut buf: &mut [u8]) {
while !buf.is_empty() {
let block: [u8; BLOCK_LEN] = self.inner.root_output_block();
let output_bytes = &block[self.position_within_block as usize..];
let take = cmp::min(buf.len(), output_bytes.len());
buf[..take].copy_from_slice(&output_bytes[..take]);
buf = &mut buf[take..];
self.position_within_block += take as u8;
if self.position_within_block == BLOCK_LEN as u8 {
self.inner.counter += 1;
self.position_within_block = 0;
}
}
}
/// Return the current read position in the output stream. The position of
/// a new `OutputReader` starts at 0, and each call to [`fill`] or
/// [`Read::read`] moves the position forward by the number of bytes read.
///
/// [`fill`]: #method.fill
/// [`Read::read`]: #method.read
pub fn position(&self) -> u64 {
self.inner.counter * BLOCK_LEN as u64 + self.position_within_block as u64
}
/// Seek to a new read position in the output stream. This is equivalent to
/// calling [`Seek::seek`] with [`SeekFrom::Start`], except that it doesn't
/// return a `Result`.
///
/// [`Seek::seek`]: #method.seek
/// [`SeekFrom::Start`]: https://doc.rust-lang.org/std/io/enum.SeekFrom.html
pub fn set_position(&mut self, position: u64) {
self.position_within_block = (position % BLOCK_LEN as u64) as u8;
self.inner.counter = position / BLOCK_LEN as u64;
}
}
// Don't derive(Debug), because the state may be secret.
impl fmt::Debug for OutputReader {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("OutputReader")
.field("position", &self.position())
.finish()
}
}
#[cfg(feature = "std")]
impl std::io::Read for OutputReader {
#[inline]
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
self.fill(buf);
Ok(buf.len())
}
}
#[cfg(feature = "std")]
impl std::io::Seek for OutputReader {
fn seek(&mut self, pos: std::io::SeekFrom) -> std::io::Result<u64> {
let max_position = u64::max_value() as i128;
let target_position: i128 = match pos {
std::io::SeekFrom::Start(x) => x as i128,
std::io::SeekFrom::Current(x) => self.position() as i128 + x as i128,
std::io::SeekFrom::End(_) => {
return Err(std::io::Error::new(
std::io::ErrorKind::InvalidInput,
"seek from end not supported",
));
}
};
if target_position < 0 {
return Err(std::io::Error::new(
std::io::ErrorKind::InvalidInput,
"seek before start",
));
}
self.set_position(cmp::min(target_position, max_position) as u64);
Ok(self.position())
}
}
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