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/*===-- blake3.c - BLAKE3 C Implementation ------------------------*- C -*-===*\
|* *|
|* Released into the public domain with CC0 1.0 *|
|* See 'llvm/lib/Support/BLAKE3/LICENSE' for info. *|
|* SPDX-License-Identifier: CC0-1.0 *|
|* *|
#include <assert.h>
#include <stdbool.h>
#include <string.h>
#include "blake3_impl.h"
const char *llvm_blake3_version(void) { return BLAKE3_VERSION_STRING; }
INLINE void chunk_state_init(blake3_chunk_state *self, const uint32_t key[8],
uint8_t flags) {
memcpy(self->cv, key, BLAKE3_KEY_LEN);
self->chunk_counter = 0;
memset(self->buf, 0, BLAKE3_BLOCK_LEN);
self->buf_len = 0;
self->blocks_compressed = 0;
self->flags = flags;
INLINE void chunk_state_reset(blake3_chunk_state *self, const uint32_t key[8],
uint64_t chunk_counter) {
memcpy(self->cv, key, BLAKE3_KEY_LEN);
self->chunk_counter = chunk_counter;
self->blocks_compressed = 0;
memset(self->buf, 0, BLAKE3_BLOCK_LEN);
self->buf_len = 0;
INLINE size_t chunk_state_len(const blake3_chunk_state *self) {
return (BLAKE3_BLOCK_LEN * (size_t)self->blocks_compressed) +
INLINE size_t chunk_state_fill_buf(blake3_chunk_state *self,
const uint8_t *input, size_t input_len) {
size_t take = BLAKE3_BLOCK_LEN - ((size_t)self->buf_len);
if (take > input_len) {
take = input_len;
uint8_t *dest = self->buf + ((size_t)self->buf_len);
memcpy(dest, input, take);
self->buf_len += (uint8_t)take;
return take;
INLINE uint8_t chunk_state_maybe_start_flag(const blake3_chunk_state *self) {
if (self->blocks_compressed == 0) {
} else {
return 0;
typedef struct {
uint32_t input_cv[8];
uint64_t counter;
uint8_t block[BLAKE3_BLOCK_LEN];
uint8_t block_len;
uint8_t flags;
} output_t;
INLINE output_t make_output(const uint32_t input_cv[8],
const uint8_t block[BLAKE3_BLOCK_LEN],
uint8_t block_len, uint64_t counter,
uint8_t flags) {
output_t ret;
memcpy(ret.input_cv, input_cv, 32);
memcpy(ret.block, block, BLAKE3_BLOCK_LEN);
ret.block_len = block_len;
ret.counter = counter;
ret.flags = flags;
return ret;
// Chaining values within a given chunk (specifically the compress_in_place
// interface) are represented as words. This avoids unnecessary bytes<->words
// conversion overhead in the portable implementation. However, the hash_many
// interface handles both user input and parent node blocks, so it accepts
// bytes. For that reason, chaining values in the CV stack are represented as
// bytes.
INLINE void output_chaining_value(const output_t *self, uint8_t cv[32]) {
uint32_t cv_words[8];
memcpy(cv_words, self->input_cv, 32);
blake3_compress_in_place(cv_words, self->block, self->block_len,
self->counter, self->flags);
store_cv_words(cv, cv_words);
INLINE void output_root_bytes(const output_t *self, uint64_t seek, uint8_t *out,
size_t out_len) {
uint64_t output_block_counter = seek / 64;
size_t offset_within_block = seek % 64;
uint8_t wide_buf[64];
while (out_len > 0) {
blake3_compress_xof(self->input_cv, self->block, self->block_len,
output_block_counter, self->flags | ROOT, wide_buf);
size_t available_bytes = 64 - offset_within_block;
size_t memcpy_len;
if (out_len > available_bytes) {
memcpy_len = available_bytes;
} else {
memcpy_len = out_len;
memcpy(out, wide_buf + offset_within_block, memcpy_len);
out += memcpy_len;
out_len -= memcpy_len;
output_block_counter += 1;
offset_within_block = 0;
INLINE void chunk_state_update(blake3_chunk_state *self, const uint8_t *input,
size_t input_len) {
if (self->buf_len > 0) {
size_t take = chunk_state_fill_buf(self, input, input_len);
input += take;
input_len -= take;
if (input_len > 0) {
self->cv, self->buf, BLAKE3_BLOCK_LEN, self->chunk_counter,
self->flags | chunk_state_maybe_start_flag(self));
self->blocks_compressed += 1;
self->buf_len = 0;
memset(self->buf, 0, BLAKE3_BLOCK_LEN);
while (input_len > BLAKE3_BLOCK_LEN) {
blake3_compress_in_place(self->cv, input, BLAKE3_BLOCK_LEN,
self->flags | chunk_state_maybe_start_flag(self));
self->blocks_compressed += 1;
input += BLAKE3_BLOCK_LEN;
input_len -= BLAKE3_BLOCK_LEN;
size_t take = chunk_state_fill_buf(self, input, input_len);
input += take;
input_len -= take;
INLINE output_t chunk_state_output(const blake3_chunk_state *self) {
uint8_t block_flags =
self->flags | chunk_state_maybe_start_flag(self) | CHUNK_END;
return make_output(self->cv, self->buf, self->buf_len, self->chunk_counter,
INLINE output_t parent_output(const uint8_t block[BLAKE3_BLOCK_LEN],
const uint32_t key[8], uint8_t flags) {
return make_output(key, block, BLAKE3_BLOCK_LEN, 0, flags | PARENT);
// 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.
INLINE size_t left_len(size_t content_len) {
// Subtract 1 to reserve at least one byte for the right side. content_len
// should always be greater than BLAKE3_CHUNK_LEN.
size_t full_chunks = (content_len - 1) / BLAKE3_CHUNK_LEN;
return round_down_to_power_of_2(full_chunks) * BLAKE3_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.
INLINE size_t compress_chunks_parallel(const uint8_t *input, size_t input_len,
const uint32_t key[8],
uint64_t chunk_counter, uint8_t flags,
uint8_t *out) {
#if defined(BLAKE3_TESTING)
assert(0 < input_len);
assert(input_len <= MAX_SIMD_DEGREE * BLAKE3_CHUNK_LEN);
const uint8_t *chunks_array[MAX_SIMD_DEGREE];
size_t input_position = 0;
size_t chunks_array_len = 0;
while (input_len - input_position >= BLAKE3_CHUNK_LEN) {
chunks_array[chunks_array_len] = &input[input_position];
input_position += BLAKE3_CHUNK_LEN;
chunks_array_len += 1;
blake3_hash_many(chunks_array, chunks_array_len,
BLAKE3_CHUNK_LEN / BLAKE3_BLOCK_LEN, key, chunk_counter,
true, 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.
if (input_len > input_position) {
uint64_t counter = chunk_counter + (uint64_t)chunks_array_len;
blake3_chunk_state chunk_state;
chunk_state_init(&chunk_state, key, flags);
chunk_state.chunk_counter = counter;
chunk_state_update(&chunk_state, &input[input_position],
input_len - input_position);
output_t output = chunk_state_output(&chunk_state);
output_chaining_value(&output, &out[chunks_array_len * BLAKE3_OUT_LEN]);
return chunks_array_len + 1;
} else {
return chunks_array_len;
// 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.
INLINE size_t compress_parents_parallel(const uint8_t *child_chaining_values,
size_t num_chaining_values,
const uint32_t key[8], uint8_t flags,
uint8_t *out) {
#if defined(BLAKE3_TESTING)
assert(2 <= num_chaining_values);
assert(num_chaining_values <= 2 * MAX_SIMD_DEGREE_OR_2);
const uint8_t *parents_array[MAX_SIMD_DEGREE_OR_2];
size_t parents_array_len = 0;
while (num_chaining_values - (2 * parents_array_len) >= 2) {
parents_array[parents_array_len] =
&child_chaining_values[2 * parents_array_len * BLAKE3_OUT_LEN];
parents_array_len += 1;
blake3_hash_many(parents_array, parents_array_len, 1, key,
0, // Parents always use counter 0.
false, flags | PARENT,
0, // Parents have no start flags.
0, // Parents have no end flags.
// If there's an odd child left over, it becomes an output.
if (num_chaining_values > 2 * parents_array_len) {
memcpy(&out[parents_array_len * BLAKE3_OUT_LEN],
&child_chaining_values[2 * parents_array_len * BLAKE3_OUT_LEN],
return parents_array_len + 1;
} else {
return parents_array_len;
// 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().
static size_t blake3_compress_subtree_wide(const uint8_t *input,
size_t input_len,
const uint32_t key[8],
uint64_t chunk_counter,
uint8_t flags, uint8_t *out) {
// Note that the single chunk case does *not* bump the SIMD degree up to 2
// when it is 1. If this implementation adds multi-threading in the future,
// this gives us the option of multi-threading even the 2-chunk case, which
// can help performance on smaller platforms.
if (input_len <= blake3_simd_degree() * BLAKE3_CHUNK_LEN) {
return compress_chunks_parallel(input, input_len, key, chunk_counter, flags,
// 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.)
size_t left_input_len = left_len(input_len);
size_t right_input_len = input_len - left_input_len;
const uint8_t *right_input = &input[left_input_len];
uint64_t right_chunk_counter =
chunk_counter + (uint64_t)(left_input_len / BLAKE3_CHUNK_LEN);
// 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.
uint8_t cv_array[2 * MAX_SIMD_DEGREE_OR_2 * BLAKE3_OUT_LEN];
size_t degree = blake3_simd_degree();
if (left_input_len > BLAKE3_CHUNK_LEN && degree == 1) {
// The special case: We always use a degree of at least two, to make
// sure there are two outputs. Except, as noted above, at the chunk
// level, where we allow degree=1. (Note that the 1-chunk-input case is
// a different codepath.)
degree = 2;
uint8_t *right_cvs = &cv_array[degree * BLAKE3_OUT_LEN];
// Recurse! If this implementation adds multi-threading support in the
// future, this is where it will go.
size_t left_n = blake3_compress_subtree_wide(input, left_input_len, key,
chunk_counter, flags, cv_array);
size_t right_n = blake3_compress_subtree_wide(
right_input, right_input_len, key, right_chunk_counter, flags, right_cvs);
// 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.
if (left_n == 1) {
memcpy(out, cv_array, 2 * BLAKE3_OUT_LEN);
return 2;
// Otherwise, do one layer of parent node compression.
size_t num_chaining_values = left_n + right_n;
return compress_parents_parallel(cv_array, num_chaining_values, key, flags,
// 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.
INLINE void compress_subtree_to_parent_node(
const uint8_t *input, size_t input_len, const uint32_t key[8],
uint64_t chunk_counter, uint8_t flags, uint8_t out[2 * BLAKE3_OUT_LEN]) {
#if defined(BLAKE3_TESTING)
assert(input_len > BLAKE3_CHUNK_LEN);
uint8_t cv_array[MAX_SIMD_DEGREE_OR_2 * BLAKE3_OUT_LEN];
size_t num_cvs = blake3_compress_subtree_wide(input, input_len, key,
chunk_counter, flags, cv_array);
assert(num_cvs <= MAX_SIMD_DEGREE_OR_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.
uint8_t out_array[MAX_SIMD_DEGREE_OR_2 * BLAKE3_OUT_LEN / 2];
// The second half of this loop condition is always true, and we just
// asserted it above. But GCC can't tell that it's always true, and if NDEBUG
// is set on platforms where MAX_SIMD_DEGREE_OR_2 == 2, GCC emits spurious
// warnings here. GCC 8.5 is particularly sensitive, so if you're changing
// this code, test it against that version.
while (num_cvs > 2 && num_cvs <= MAX_SIMD_DEGREE_OR_2) {
num_cvs =
compress_parents_parallel(cv_array, num_cvs, key, flags, out_array);
memcpy(cv_array, out_array, num_cvs * BLAKE3_OUT_LEN);
memcpy(out, cv_array, 2 * BLAKE3_OUT_LEN);
INLINE void hasher_init_base(blake3_hasher *self, const uint32_t key[8],
uint8_t flags) {
memcpy(self->key, key, BLAKE3_KEY_LEN);
chunk_state_init(&self->chunk, key, flags);
self->cv_stack_len = 0;
void llvm_blake3_hasher_init(blake3_hasher *self) { hasher_init_base(self, IV, 0); }
void llvm_blake3_hasher_init_keyed(blake3_hasher *self,
const uint8_t key[BLAKE3_KEY_LEN]) {
uint32_t key_words[8];
load_key_words(key, key_words);
hasher_init_base(self, key_words, KEYED_HASH);
void llvm_blake3_hasher_init_derive_key_raw(blake3_hasher *self, const void *context,
size_t context_len) {
blake3_hasher context_hasher;
hasher_init_base(&context_hasher, IV, DERIVE_KEY_CONTEXT);
llvm_blake3_hasher_update(&context_hasher, context, context_len);
uint8_t context_key[BLAKE3_KEY_LEN];
llvm_blake3_hasher_finalize(&context_hasher, context_key, BLAKE3_KEY_LEN);
uint32_t context_key_words[8];
load_key_words(context_key, context_key_words);
hasher_init_base(self, context_key_words, DERIVE_KEY_MATERIAL);
void llvm_blake3_hasher_init_derive_key(blake3_hasher *self, const char *context) {
llvm_blake3_hasher_init_derive_key_raw(self, context, strlen(context));
// As described in hasher_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.
INLINE void hasher_merge_cv_stack(blake3_hasher *self, uint64_t total_len) {
size_t post_merge_stack_len = (size_t)popcnt(total_len);
while (self->cv_stack_len > post_merge_stack_len) {
uint8_t *parent_node =
&self->cv_stack[(self->cv_stack_len - 2) * BLAKE3_OUT_LEN];
output_t output = parent_output(parent_node, self->key, self->chunk.flags);
output_chaining_value(&output, parent_node);
self->cv_stack_len -= 1;
// In, 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.)
INLINE void hasher_push_cv(blake3_hasher *self, uint8_t new_cv[BLAKE3_OUT_LEN],
uint64_t chunk_counter) {
hasher_merge_cv_stack(self, chunk_counter);
memcpy(&self->cv_stack[self->cv_stack_len * BLAKE3_OUT_LEN], new_cv,
self->cv_stack_len += 1;
void llvm_blake3_hasher_update(blake3_hasher *self, const void *input,
size_t input_len) {
// Explicitly checking for zero avoids causing UB by passing a null pointer
// to memcpy. This comes up in practice with things like:
// std::vector<uint8_t> v;
// blake3_hasher_update(&hasher,, v.size());
if (input_len == 0) {
const uint8_t *input_bytes = (const uint8_t *)input;
// If we have some partial chunk bytes in the internal chunk_state, we need
// to finish that chunk first.
if (chunk_state_len(&self->chunk) > 0) {
size_t take = BLAKE3_CHUNK_LEN - chunk_state_len(&self->chunk);
if (take > input_len) {
take = input_len;
chunk_state_update(&self->chunk, input_bytes, take);
input_bytes += take;
input_len -= take;
// If we've filled the current chunk and there's more coming, finalize this
// chunk and proceed. In this case we know it's not the root.
if (input_len > 0) {
output_t output = chunk_state_output(&self->chunk);
uint8_t chunk_cv[32];
output_chaining_value(&output, chunk_cv);
hasher_push_cv(self, chunk_cv, self->chunk.chunk_counter);
chunk_state_reset(&self->chunk, self->key, self->chunk.chunk_counter + 1);
} else {
// 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 maybe in the future,
// 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 > BLAKE3_CHUNK_LEN) {
size_t subtree_len = round_down_to_power_of_2(input_len);
uint64_t count_so_far = self->chunk.chunk_counter * BLAKE3_CHUNK_LEN;
// 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
while ((((uint64_t)(subtree_len - 1)) & 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.
uint64_t subtree_chunks = subtree_len / BLAKE3_CHUNK_LEN;
if (subtree_len <= BLAKE3_CHUNK_LEN) {
blake3_chunk_state chunk_state;
chunk_state_init(&chunk_state, self->key, self->chunk.flags);
chunk_state.chunk_counter = self->chunk.chunk_counter;
chunk_state_update(&chunk_state, input_bytes, subtree_len);
output_t output = chunk_state_output(&chunk_state);
uint8_t cv[BLAKE3_OUT_LEN];
output_chaining_value(&output, cv);
hasher_push_cv(self, cv, 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.
uint8_t cv_pair[2 * BLAKE3_OUT_LEN];
compress_subtree_to_parent_node(input_bytes, subtree_len, self->key,
self->chunk.flags, cv_pair);
hasher_push_cv(self, cv_pair, self->chunk.chunk_counter);
hasher_push_cv(self, &cv_pair[BLAKE3_OUT_LEN],
self->chunk.chunk_counter + (subtree_chunks / 2));
self->chunk.chunk_counter += subtree_chunks;
input_bytes += subtree_len;
input_len -= subtree_len;
// If there's any remaining input less than a full chunk, add it to the chunk
// state. In that case, also do a final merge loop to make sure the subtree
// stack doesn't contain any unmerged pairs. The remaining input means we
// know these merges are non-root. This merge loop isn't strictly necessary
// here, because hasher_push_chunk_cv already does its own merge loop, but it
// simplifies blake3_hasher_finalize below.
if (input_len > 0) {
chunk_state_update(&self->chunk, input_bytes, input_len);
hasher_merge_cv_stack(self, self->chunk.chunk_counter);
void llvm_blake3_hasher_finalize(const blake3_hasher *self, uint8_t *out,
size_t out_len) {
llvm_blake3_hasher_finalize_seek(self, 0, out, out_len);
// Avoid false positives due to uninstrumented assembly code.
__msan_unpoison(out, out_len);
void llvm_blake3_hasher_finalize_seek(const blake3_hasher *self, uint64_t seek,
uint8_t *out, size_t out_len) {
// Explicitly checking for zero avoids causing UB by passing a null pointer
// to memcpy. This comes up in practice with things like:
// std::vector<uint8_t> v;
// blake3_hasher_finalize(&hasher,, v.size());
if (out_len == 0) {
// If the subtree stack is empty, then the current chunk is the root.
if (self->cv_stack_len == 0) {
output_t output = chunk_state_output(&self->chunk);
output_root_bytes(&output, seek, out, out_len);
// If there are any bytes in the chunk state, finalize that chunk and do a
// roll-up merge between that chunk hash and every subtree in the stack. In
// this case, the extra merge loop at the end of blake3_hasher_update
// guarantees that none of the subtrees in the stack need to be merged with
// each other first. Otherwise, if there are no bytes in the chunk state,
// then the top of the stack is a chunk hash, and we start the merge from
// that.
output_t output;
size_t cvs_remaining;
if (chunk_state_len(&self->chunk) > 0) {
cvs_remaining = self->cv_stack_len;
output = chunk_state_output(&self->chunk);
} else {
// There are always at least 2 CVs in the stack in this case.
cvs_remaining = self->cv_stack_len - 2;
output = parent_output(&self->cv_stack[cvs_remaining * 32], self->key,
while (cvs_remaining > 0) {
cvs_remaining -= 1;
uint8_t parent_block[BLAKE3_BLOCK_LEN];
memcpy(parent_block, &self->cv_stack[cvs_remaining * 32], 32);
output_chaining_value(&output, &parent_block[32]);
output = parent_output(parent_block, self->key, self->chunk.flags);
output_root_bytes(&output, seek, out, out_len);
void llvm_blake3_hasher_reset(blake3_hasher *self) {
chunk_state_reset(&self->chunk, self->key, 0);
self->cv_stack_len = 0;