Description: Add reference implementation from upstream
 as it is not included in the crates.io package, but needed by tests.
 Last grabbed at commit 4ec3be8bfa6574fcd30619741390847ddc037d55
Last-Update: 2025-04-09
---
This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
--- /dev/null
+++ b/reference_impl/reference_impl.rs
@@ -0,0 +1,374 @@
+//! This is the reference implementation of BLAKE3. It is used for testing and
+//! as a readable example of the algorithms involved. Section 5.1 of [the BLAKE3
+//! spec](https://github.com/BLAKE3-team/BLAKE3-specs/blob/master/blake3.pdf)
+//! discusses this implementation. You can render docs for this implementation
+//! by running `cargo doc --open` in this directory.
+//!
+//! # Example
+//!
+//! ```
+//! let mut hasher = reference_impl::Hasher::new();
+//! hasher.update(b"abc");
+//! hasher.update(b"def");
+//! let mut hash = [0; 32];
+//! hasher.finalize(&mut hash);
+//! let mut extended_hash = [0; 500];
+//! hasher.finalize(&mut extended_hash);
+//! assert_eq!(hash, extended_hash[..32]);
+//! ```
+
+use core::cmp::min;
+
+const OUT_LEN: usize = 32;
+const KEY_LEN: usize = 32;
+const BLOCK_LEN: usize = 64;
+const CHUNK_LEN: usize = 1024;
+
+const CHUNK_START: u32 = 1 << 0;
+const CHUNK_END: u32 = 1 << 1;
+const PARENT: u32 = 1 << 2;
+const ROOT: u32 = 1 << 3;
+const KEYED_HASH: u32 = 1 << 4;
+const DERIVE_KEY_CONTEXT: u32 = 1 << 5;
+const DERIVE_KEY_MATERIAL: u32 = 1 << 6;
+
+const IV: [u32; 8] = [
+    0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19,
+];
+
+const MSG_PERMUTATION: [usize; 16] = [2, 6, 3, 10, 7, 0, 4, 13, 1, 11, 12, 5, 9, 14, 15, 8];
+
+// The mixing function, G, which mixes either a column or a diagonal.
+fn g(state: &mut [u32; 16], a: usize, b: usize, c: usize, d: usize, mx: u32, my: u32) {
+    state[a] = state[a].wrapping_add(state[b]).wrapping_add(mx);
+    state[d] = (state[d] ^ state[a]).rotate_right(16);
+    state[c] = state[c].wrapping_add(state[d]);
+    state[b] = (state[b] ^ state[c]).rotate_right(12);
+    state[a] = state[a].wrapping_add(state[b]).wrapping_add(my);
+    state[d] = (state[d] ^ state[a]).rotate_right(8);
+    state[c] = state[c].wrapping_add(state[d]);
+    state[b] = (state[b] ^ state[c]).rotate_right(7);
+}
+
+fn round(state: &mut [u32; 16], m: &[u32; 16]) {
+    // Mix the columns.
+    g(state, 0, 4, 8, 12, m[0], m[1]);
+    g(state, 1, 5, 9, 13, m[2], m[3]);
+    g(state, 2, 6, 10, 14, m[4], m[5]);
+    g(state, 3, 7, 11, 15, m[6], m[7]);
+    // Mix the diagonals.
+    g(state, 0, 5, 10, 15, m[8], m[9]);
+    g(state, 1, 6, 11, 12, m[10], m[11]);
+    g(state, 2, 7, 8, 13, m[12], m[13]);
+    g(state, 3, 4, 9, 14, m[14], m[15]);
+}
+
+fn permute(m: &mut [u32; 16]) {
+    let mut permuted = [0; 16];
+    for i in 0..16 {
+        permuted[i] = m[MSG_PERMUTATION[i]];
+    }
+    *m = permuted;
+}
+
+fn compress(
+    chaining_value: &[u32; 8],
+    block_words: &[u32; 16],
+    counter: u64,
+    block_len: u32,
+    flags: u32,
+) -> [u32; 16] {
+    let counter_low = counter as u32;
+    let counter_high = (counter >> 32) as u32;
+    #[rustfmt::skip]
+    let mut state = [
+        chaining_value[0], chaining_value[1], chaining_value[2], chaining_value[3],
+        chaining_value[4], chaining_value[5], chaining_value[6], chaining_value[7],
+        IV[0],             IV[1],             IV[2],             IV[3],
+        counter_low,       counter_high,      block_len,         flags,
+    ];
+    let mut block = *block_words;
+
+    round(&mut state, &block); // round 1
+    permute(&mut block);
+    round(&mut state, &block); // round 2
+    permute(&mut block);
+    round(&mut state, &block); // round 3
+    permute(&mut block);
+    round(&mut state, &block); // round 4
+    permute(&mut block);
+    round(&mut state, &block); // round 5
+    permute(&mut block);
+    round(&mut state, &block); // round 6
+    permute(&mut block);
+    round(&mut state, &block); // round 7
+
+    for i in 0..8 {
+        state[i] ^= state[i + 8];
+        state[i + 8] ^= chaining_value[i];
+    }
+    state
+}
+
+fn first_8_words(compression_output: [u32; 16]) -> [u32; 8] {
+    compression_output[0..8].try_into().unwrap()
+}
+
+fn words_from_little_endian_bytes(bytes: &[u8], words: &mut [u32]) {
+    debug_assert_eq!(bytes.len(), 4 * words.len());
+    for (four_bytes, word) in bytes.chunks_exact(4).zip(words) {
+        *word = u32::from_le_bytes(four_bytes.try_into().unwrap());
+    }
+}
+
+// Each chunk or parent node can produce either an 8-word 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.
+struct Output {
+    input_chaining_value: [u32; 8],
+    block_words: [u32; 16],
+    counter: u64,
+    block_len: u32,
+    flags: u32,
+}
+
+impl Output {
+    fn chaining_value(&self) -> [u32; 8] {
+        first_8_words(compress(
+            &self.input_chaining_value,
+            &self.block_words,
+            self.counter,
+            self.block_len,
+            self.flags,
+        ))
+    }
+
+    fn root_output_bytes(&self, out_slice: &mut [u8]) {
+        let mut output_block_counter = 0;
+        for out_block in out_slice.chunks_mut(2 * OUT_LEN) {
+            let words = compress(
+                &self.input_chaining_value,
+                &self.block_words,
+                output_block_counter,
+                self.block_len,
+                self.flags | ROOT,
+            );
+            // The output length might not be a multiple of 4.
+            for (word, out_word) in words.iter().zip(out_block.chunks_mut(4)) {
+                out_word.copy_from_slice(&word.to_le_bytes()[..out_word.len()]);
+            }
+            output_block_counter += 1;
+        }
+    }
+}
+
+struct ChunkState {
+    chaining_value: [u32; 8],
+    chunk_counter: u64,
+    block: [u8; BLOCK_LEN],
+    block_len: u8,
+    blocks_compressed: u8,
+    flags: u32,
+}
+
+impl ChunkState {
+    fn new(key_words: [u32; 8], chunk_counter: u64, flags: u32) -> Self {
+        Self {
+            chaining_value: key_words,
+            chunk_counter,
+            block: [0; BLOCK_LEN],
+            block_len: 0,
+            blocks_compressed: 0,
+            flags,
+        }
+    }
+
+    fn len(&self) -> usize {
+        BLOCK_LEN * self.blocks_compressed as usize + self.block_len as usize
+    }
+
+    fn start_flag(&self) -> u32 {
+        if self.blocks_compressed == 0 {
+            CHUNK_START
+        } else {
+            0
+        }
+    }
+
+    fn update(&mut self, mut input: &[u8]) {
+        while !input.is_empty() {
+            // If the block buffer is full, compress it and clear it. More
+            // input is coming, so this compression is not CHUNK_END.
+            if self.block_len as usize == BLOCK_LEN {
+                let mut block_words = [0; 16];
+                words_from_little_endian_bytes(&self.block, &mut block_words);
+                self.chaining_value = first_8_words(compress(
+                    &self.chaining_value,
+                    &block_words,
+                    self.chunk_counter,
+                    BLOCK_LEN as u32,
+                    self.flags | self.start_flag(),
+                ));
+                self.blocks_compressed += 1;
+                self.block = [0; BLOCK_LEN];
+                self.block_len = 0;
+            }
+
+            // Copy input bytes into the block buffer.
+            let want = BLOCK_LEN - self.block_len as usize;
+            let take = min(want, input.len());
+            self.block[self.block_len as usize..][..take].copy_from_slice(&input[..take]);
+            self.block_len += take as u8;
+            input = &input[take..];
+        }
+    }
+
+    fn output(&self) -> Output {
+        let mut block_words = [0; 16];
+        words_from_little_endian_bytes(&self.block, &mut block_words);
+        Output {
+            input_chaining_value: self.chaining_value,
+            block_words,
+            counter: self.chunk_counter,
+            block_len: self.block_len as u32,
+            flags: self.flags | self.start_flag() | CHUNK_END,
+        }
+    }
+}
+
+fn parent_output(
+    left_child_cv: [u32; 8],
+    right_child_cv: [u32; 8],
+    key_words: [u32; 8],
+    flags: u32,
+) -> Output {
+    let mut block_words = [0; 16];
+    block_words[..8].copy_from_slice(&left_child_cv);
+    block_words[8..].copy_from_slice(&right_child_cv);
+    Output {
+        input_chaining_value: key_words,
+        block_words,
+        counter: 0,                  // Always 0 for parent nodes.
+        block_len: BLOCK_LEN as u32, // Always BLOCK_LEN (64) for parent nodes.
+        flags: PARENT | flags,
+    }
+}
+
+fn parent_cv(
+    left_child_cv: [u32; 8],
+    right_child_cv: [u32; 8],
+    key_words: [u32; 8],
+    flags: u32,
+) -> [u32; 8] {
+    parent_output(left_child_cv, right_child_cv, key_words, flags).chaining_value()
+}
+
+/// An incremental hasher that can accept any number of writes.
+pub struct Hasher {
+    chunk_state: ChunkState,
+    key_words: [u32; 8],
+    cv_stack: [[u32; 8]; 54], // Space for 54 subtree chaining values:
+    cv_stack_len: u8,         // 2^54 * CHUNK_LEN = 2^64
+    flags: u32,
+}
+
+impl Hasher {
+    fn new_internal(key_words: [u32; 8], flags: u32) -> Self {
+        Self {
+            chunk_state: ChunkState::new(key_words, 0, flags),
+            key_words,
+            cv_stack: [[0; 8]; 54],
+            cv_stack_len: 0,
+            flags,
+        }
+    }
+
+    /// 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.
+    pub fn new_keyed(key: &[u8; KEY_LEN]) -> Self {
+        let mut key_words = [0; 8];
+        words_from_little_endian_bytes(key, &mut key_words);
+        Self::new_internal(key_words, KEYED_HASH)
+    }
+
+    /// Construct a new `Hasher` for the key derivation function. The context
+    /// string should be hardcoded, globally unique, and application-specific.
+    pub fn new_derive_key(context: &str) -> Self {
+        let mut context_hasher = Self::new_internal(IV, DERIVE_KEY_CONTEXT);
+        context_hasher.update(context.as_bytes());
+        let mut context_key = [0; KEY_LEN];
+        context_hasher.finalize(&mut context_key);
+        let mut context_key_words = [0; 8];
+        words_from_little_endian_bytes(&context_key, &mut context_key_words);
+        Self::new_internal(context_key_words, DERIVE_KEY_MATERIAL)
+    }
+
+    fn push_stack(&mut self, cv: [u32; 8]) {
+        self.cv_stack[self.cv_stack_len as usize] = cv;
+        self.cv_stack_len += 1;
+    }
+
+    fn pop_stack(&mut self) -> [u32; 8] {
+        self.cv_stack_len -= 1;
+        self.cv_stack[self.cv_stack_len as usize]
+    }
+
+    // Section 5.1.2 of the BLAKE3 spec explains this algorithm in more detail.
+    fn add_chunk_chaining_value(&mut self, mut new_cv: [u32; 8], mut total_chunks: u64) {
+        // This chunk might complete some subtrees. For each completed subtree,
+        // its left child will be the current top entry in the CV stack, and
+        // its right child will be the current value of `new_cv`. Pop each left
+        // child off the stack, merge it with `new_cv`, and overwrite `new_cv`
+        // with the result. After all these merges, push the final value of
+        // `new_cv` onto the stack. The number of completed subtrees is given
+        // by the number of trailing 0-bits in the new total number of chunks.
+        while total_chunks & 1 == 0 {
+            new_cv = parent_cv(self.pop_stack(), new_cv, self.key_words, self.flags);
+            total_chunks >>= 1;
+        }
+        self.push_stack(new_cv);
+    }
+
+    /// Add input to the hash state. This can be called any number of times.
+    pub fn update(&mut self, mut input: &[u8]) {
+        while !input.is_empty() {
+            // If the current chunk is complete, finalize it and reset the
+            // chunk state. More input is coming, so this chunk is not ROOT.
+            if self.chunk_state.len() == CHUNK_LEN {
+                let chunk_cv = self.chunk_state.output().chaining_value();
+                let total_chunks = self.chunk_state.chunk_counter + 1;
+                self.add_chunk_chaining_value(chunk_cv, total_chunks);
+                self.chunk_state = ChunkState::new(self.key_words, total_chunks, self.flags);
+            }
+
+            // Compress input bytes into the current chunk state.
+            let want = CHUNK_LEN - self.chunk_state.len();
+            let take = min(want, input.len());
+            self.chunk_state.update(&input[..take]);
+            input = &input[take..];
+        }
+    }
+
+    /// Finalize the hash and write any number of output bytes.
+    pub fn finalize(&self, out_slice: &mut [u8]) {
+        // Starting with the Output from the current chunk, compute all the
+        // parent chaining values along the right edge of the tree, until we
+        // have the root Output.
+        let mut output = self.chunk_state.output();
+        let mut parent_nodes_remaining = self.cv_stack_len as usize;
+        while parent_nodes_remaining > 0 {
+            parent_nodes_remaining -= 1;
+            output = parent_output(
+                self.cv_stack[parent_nodes_remaining],
+                output.chaining_value(),
+                self.key_words,
+                self.flags,
+            );
+        }
+        output.root_output_bytes(out_slice);
+    }
+}
--- a/benches/bench.rs
+++ b/benches/bench.rs
@@ -3,2 +3,4 @@
 extern crate test;
+#[path = "../reference_impl/reference_impl.rs"]
+mod reference_impl;
 
--- a/src/test.rs
+++ b/src/test.rs
@@ -1 +1,4 @@
+#[path = "../reference_impl/reference_impl.rs"]
+mod reference_impl;
+
 use crate::{CVBytes, CVWords, IncrementCounter, BLOCK_LEN, CHUNK_LEN, OUT_LEN};