diff options
Diffstat (limited to '3rdparty/BLAKE3/c/blake3.c')
| -rw-r--r-- | 3rdparty/BLAKE3/c/blake3.c | 607 |
1 files changed, 607 insertions, 0 deletions
diff --git a/3rdparty/BLAKE3/c/blake3.c b/3rdparty/BLAKE3/c/blake3.c new file mode 100644 index 000000000..7abf5324e --- /dev/null +++ b/3rdparty/BLAKE3/c/blake3.c @@ -0,0 +1,607 @@ +#include <assert.h> +#include <stdbool.h> +#include <string.h> + +#include "blake3.h" +#include "blake3_impl.h" + +const char * 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) + + ((size_t)self->buf_len); +} + +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) { + return CHUNK_START; + } 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) { + blake3_compress_in_place( + 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->chunk_counter, + 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, + block_flags); +} + +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); +#endif + + 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); +#endif + + 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. + out); + + // 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], + 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, + 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.) + 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, + 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. +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); +#endif + + 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); + + // 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]; + while (num_cvs > 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 blake3_hasher_init(blake3_hasher *self) { hasher_init_base(self, IV, 0); } + +void 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 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); + blake3_hasher_update(&context_hasher, context, context_len); + uint8_t context_key[BLAKE3_KEY_LEN]; + 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 blake3_hasher_init_derive_key(blake3_hasher *self, const char *context) { + 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 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.) +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, + BLAKE3_OUT_LEN); + self->cv_stack_len += 1; +} + +void 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.data(), v.size()); + if (input_len == 0) { + return; + } + + 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 { + return; + } + } + + // 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 + // https://github.com/BLAKE3-team/BLAKE3/issues/69. + 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.chunk_counter, + 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 blake3_hasher_finalize(const blake3_hasher *self, uint8_t *out, + size_t out_len) { + blake3_hasher_finalize_seek(self, 0, out, out_len); +} + +void 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.data(), v.size()); + if (out_len == 0) { + return; + } + + // 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); + return; + } + // 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, + self->chunk.flags); + } + 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); +} |