[Support] Introduce the BLAKE3 hashing function implementation

BLAKE3 is a cryptographic hash function that is secure and very performant.
The C implementation originates from https://github.com/BLAKE3-team/BLAKE3/tree/1.3.1/c
License is at https://github.com/BLAKE3-team/BLAKE3/blob/1.3.1/LICENSE

This patch adds:

* `llvm/include/llvm-c/blake3.h`: The BLAKE3 C API
* `llvm/include/llvm/Support/BLAKE3.h`: C++ wrapper of the C API
* `llvm/lib/Support/BLAKE3`: Directory containing the BLAKE3 C implementation files, including the `LICENSE` file
* `llvm/unittests/Support/BLAKE3Test.cpp`: unit tests for the BLAKE3 C++ wrapper

This initial patch contains the pristine BLAKE3 sources, a follow-up patch will introduce
LLVM-specific prefixes to avoid conflicts if a client also links with its own BLAKE3 version.

And here's some timings comparing BLAKE3 with LLVM's SHA1/SHA256/MD5.
Timings include `AVX512`, `AVX2`, `neon`, and the generic/portable implementations.
The table shows the speed-up multiplier of BLAKE3 for hashing 100 MBs:

|        Processor        | SHA1  | SHA256 |  MD5 |
|-------------------------|-------|--------|------|
| Intel Xeon W (AVX512)   | 10.4x |   27x  | 9.4x |
| Intel Xeon W (AVX2)     | 6.5x  |   17x  | 5.9x |
| Intel Xeon W (portable) | 1.3x  |  3.3x  | 1.1x |
|      M1Pro (neon)       | 2.1x  |  4.7x  | 2.8x |
|      M1Pro (portable)   | 1.1x  |  2.4x  | 1.5x |

Differential Revision: https://reviews.llvm.org/D121510

llvm/include/llvm-c/blake3.h

+#ifndef BLAKE3_H
+#define BLAKE3_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define BLAKE3_VERSION_STRING "1.3.1"
+#define BLAKE3_KEY_LEN 32
+#define BLAKE3_OUT_LEN 32
+#define BLAKE3_BLOCK_LEN 64
+#define BLAKE3_CHUNK_LEN 1024
+#define BLAKE3_MAX_DEPTH 54
+
+// This struct is a private implementation detail. It has to be here because
+// it's part of blake3_hasher below.
+typedef struct {
+  uint32_t cv[8];
+  uint64_t chunk_counter;
+  uint8_t buf[BLAKE3_BLOCK_LEN];
+  uint8_t buf_len;
+  uint8_t blocks_compressed;
+  uint8_t flags;
+} blake3_chunk_state;
+
+typedef struct {
+  uint32_t key[8];
+  blake3_chunk_state chunk;
+  uint8_t cv_stack_len;
+  // 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.
+  uint8_t cv_stack[(BLAKE3_MAX_DEPTH + 1) * BLAKE3_OUT_LEN];
+} blake3_hasher;
+
+const char *blake3_version(void);
+void blake3_hasher_init(blake3_hasher *self);
+void blake3_hasher_init_keyed(blake3_hasher *self,
+                              const uint8_t key[BLAKE3_KEY_LEN]);
+void blake3_hasher_init_derive_key(blake3_hasher *self, const char *context);
+void blake3_hasher_init_derive_key_raw(blake3_hasher *self, const void *context,
+                                       size_t context_len);
+void blake3_hasher_update(blake3_hasher *self, const void *input,
+                          size_t input_len);
+void blake3_hasher_finalize(const blake3_hasher *self, uint8_t *out,
+                            size_t out_len);
+void blake3_hasher_finalize_seek(const blake3_hasher *self, uint64_t seek,
+                                 uint8_t *out, size_t out_len);
+void blake3_hasher_reset(blake3_hasher *self);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* BLAKE3_H */

llvm/include/llvm/Support/BLAKE3.h

+//==- BLAKE3.h - BLAKE3 C++ wrapper for LLVM ---------------------*- C++ -*-==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This is a C++ wrapper of the BLAKE3 C interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_BLAKE3_H
+#define LLVM_SUPPORT_BLAKE3_H
+
+#include "llvm-c/blake3.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+
+namespace llvm {
+
+/// The constant \p BLAKE3_OUT_LEN provides the default output length,
+/// 32 bytes, which is recommended for most callers.
+///
+/// Outputs shorter than the default length of 32 bytes (256 bits) provide
+/// less security. An N-bit BLAKE3 output is intended to provide N bits of
+/// first and second preimage resistance and N/2 bits of collision
+/// resistance, for any N up to 256. Longer outputs don't provide any
+/// additional security.
+///
+/// Shorter BLAKE3 outputs are prefixes of longer ones. Explicitly
+/// requesting a short output is equivalent to truncating the default-length
+/// output.
+template <size_t NumBytes = BLAKE3_OUT_LEN>
+using BLAKE3Result = std::array<uint8_t, NumBytes>;
+
+/// A class that wrap the BLAKE3 algorithm.
+class BLAKE3 {
+public:
+  BLAKE3() { init(); }
+
+  /// Reinitialize the internal state
+  void init() { blake3_hasher_init(&Hasher); }
+
+  /// Digest more data.
+  void update(ArrayRef<uint8_t> Data) {
+    blake3_hasher_update(&Hasher, Data.data(), Data.size());
+  }
+
+  /// Digest more data.
+  void update(StringRef Str) {
+    blake3_hasher_update(&Hasher, Str.data(), Str.size());
+  }
+
+  /// Finalize the hasher and put the result in \p Result.
+  /// This doesn't modify the hasher itself, and it's possible to finalize again
+  /// after adding more input.
+  template <size_t NumBytes = BLAKE3_OUT_LEN>
+  void final(BLAKE3Result<NumBytes> &Result) {
+    blake3_hasher_finalize(&Hasher, Result.data(), Result.size());
+  }
+
+  /// Finalize the hasher and return an output of any length, given in bytes.
+  /// This doesn't modify the hasher itself, and it's possible to finalize again
+  /// after adding more input.
+  template <size_t NumBytes = BLAKE3_OUT_LEN> BLAKE3Result<NumBytes> final() {
+    BLAKE3Result<NumBytes> Result;
+    blake3_hasher_finalize(&Hasher, Result.data(), Result.size());
+    return Result;
+  }
+
+  /// Returns a BLAKE3 hash for the given data.
+  template <size_t NumBytes = BLAKE3_OUT_LEN>
+  static BLAKE3Result<NumBytes> hash(ArrayRef<uint8_t> Data) {
+    BLAKE3 Hasher;
+    Hasher.update(Data);
+    return Hasher.final<NumBytes>();
+  }
+
+private:
+  blake3_hasher Hasher;
+};
+
+} // namespace llvm
+
+#endif

llvm/lib/Support/BLAKE3/.clang-format

+DisableFormat: true
+SortIncludes: Never

llvm/lib/Support/BLAKE3/CMakeLists.txt

+set(LLVM_BLAKE3_FILES
+  BLAKE3/blake3.c
+  BLAKE3/blake3_dispatch.c
+  BLAKE3/blake3_portable.c
+)
+
+# The BLAKE3 team recommends using the assembly versions, from the README:
+#
+# "For each of the x86 SIMD instruction sets, four versions are available:
+# three flavors of assembly (Unix, Windows MSVC, and Windows GNU) and one
+# version using C intrinsics. The assembly versions are generally
+# preferred. They perform better, they perform more consistently across
+# different compilers, and they build more quickly."
+if (CMAKE_SYSTEM_PROCESSOR MATCHES "^(x86_64|AMD64)$")
+  if (MSVC)
+    list(APPEND LLVM_BLAKE3_FILES
+      BLAKE3/blake3_sse2_x86-64_windows_msvc.asm
+      BLAKE3/blake3_sse41_x86-64_windows_msvc.asm
+      BLAKE3/blake3_avx2_x86-64_windows_msvc.asm
+      BLAKE3/blake3_avx512_x86-64_windows_msvc.asm
+    )
+  elseif(WIN32)
+    list(APPEND LLVM_BLAKE3_FILES
+      BLAKE3/blake3_sse2_x86-64_windows_gnu.S
+      BLAKE3/blake3_sse41_x86-64_windows_gnu.S
+      BLAKE3/blake3_avx2_x86-64_windows_gnu.S
+      BLAKE3/blake3_avx512_x86-64_windows_gnu.S
+    )
+  else()
+    list(APPEND LLVM_BLAKE3_FILES
+      BLAKE3/blake3_sse2_x86-64_unix.S
+      BLAKE3/blake3_sse41_x86-64_unix.S
+      BLAKE3/blake3_avx2_x86-64_unix.S
+      BLAKE3/blake3_avx512_x86-64_unix.S
+    )
+  endif()
+endif()
+
+if (CMAKE_SYSTEM_PROCESSOR MATCHES "arm")
+  list(APPEND LLVM_BLAKE3_FILES
+    BLAKE3/blake3_neon.c
+  )
+endif()
+
+set(LLVM_BLAKE3_FILES
+  ${LLVM_BLAKE3_FILES}
+  PARENT_SCOPE
+)

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llvm/lib/Support/BLAKE3/README.md

+The official C implementation of BLAKE3.
+
+# Example
+
+An example program that hashes bytes from standard input and prints the
+result:
+
+```c
+#include "blake3.h"
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+int main() {
+  // Initialize the hasher.
+  blake3_hasher hasher;
+  blake3_hasher_init(&hasher);
+
+  // Read input bytes from stdin.
+  unsigned char buf[65536];
+  while (1) {
+    ssize_t n = read(STDIN_FILENO, buf, sizeof(buf));
+    if (n > 0) {
+      blake3_hasher_update(&hasher, buf, n);
+    } else if (n == 0) {
+      break; // end of file
+    } else {
+      fprintf(stderr, "read failed: %s\n", strerror(errno));
+      exit(1);
+    }
+  }
+
+  // Finalize the hash. BLAKE3_OUT_LEN is the default output length, 32 bytes.
+  uint8_t output[BLAKE3_OUT_LEN];
+  blake3_hasher_finalize(&hasher, output, BLAKE3_OUT_LEN);
+
+  // Print the hash as hexadecimal.
+  for (size_t i = 0; i < BLAKE3_OUT_LEN; i++) {
+    printf("%02x", output[i]);
+  }
+  printf("\n");
+  return 0;
+}
+```
+
+The code above is included in this directory as `example.c`. If you're
+on x86\_64 with a Unix-like OS, you can compile a working binary like
+this:
+
+```bash
+gcc -O3 -o example example.c blake3.c blake3_dispatch.c blake3_portable.c \
+    blake3_sse2_x86-64_unix.S blake3_sse41_x86-64_unix.S blake3_avx2_x86-64_unix.S \
+    blake3_avx512_x86-64_unix.S
+```
+
+# API
+
+## The Struct
+
+```c
+typedef struct {
+  // private fields
+} blake3_hasher;
+```
+
+An incremental BLAKE3 hashing state, which can accept any number of
+updates. This implementation doesn't allocate any heap memory, but
+`sizeof(blake3_hasher)` itself is relatively large, currently 1912 bytes
+on x86-64. This size can be reduced by restricting the maximum input
+length, as described in Section 5.4 of [the BLAKE3
+spec](https://github.com/BLAKE3-team/BLAKE3-specs/blob/master/blake3.pdf),
+but this implementation doesn't currently support that strategy.
+
+## Common API Functions
+
+```c
+void blake3_hasher_init(
+  blake3_hasher *self);
+```
+
+Initialize a `blake3_hasher` in the default hashing mode.
+
+---
+
+```c
+void blake3_hasher_update(
+  blake3_hasher *self,
+  const void *input,
+  size_t input_len);
+```
+
+Add input to the hasher. This can be called any number of times.
+
+---
+
+```c
+void blake3_hasher_finalize(
+  const blake3_hasher *self,
+  uint8_t *out,
+  size_t out_len);
+```
+
+Finalize the hasher and return an output of any length, given in bytes.
+This doesn't modify the hasher itself, and it's possible to finalize
+again after adding more input. The constant `BLAKE3_OUT_LEN` provides
+the default output length, 32 bytes, which is recommended for most
+callers.
+
+Outputs shorter than the default length of 32 bytes (256 bits) provide
+less security. An N-bit BLAKE3 output is intended to provide N bits of
+first and second preimage resistance and N/2 bits of collision
+resistance, for any N up to 256. Longer outputs don't provide any
+additional security.
+
+Shorter BLAKE3 outputs are prefixes of longer ones. Explicitly
+requesting a short output is equivalent to truncating the default-length
+output. (Note that this is different between BLAKE2 and BLAKE3.)
+
+## Less Common API Functions
+
+```c
+void blake3_hasher_init_keyed(
+  blake3_hasher *self,
+  const uint8_t key[BLAKE3_KEY_LEN]);
+```
+
+Initialize a `blake3_hasher` in the keyed hashing mode. The key must be
+exactly 32 bytes.
+
+---
+
+```c
+void blake3_hasher_init_derive_key(
+  blake3_hasher *self,
+  const char *context);
+```
+
+Initialize a `blake3_hasher` in the key derivation mode. The context
+string is given as an initialization parameter, and afterwards input key
+material should be given with `blake3_hasher_update`. The context string
+is a null-terminated C string which should be **hardcoded, globally
+unique, and application-specific**. The context string should not
+include any dynamic input like salts, nonces, or identifiers read from a
+database at runtime. A good default format for the context string is
+`"[application] [commit timestamp] [purpose]"`, e.g., `"example.com
+2019-12-25 16:18:03 session tokens v1"`.
+
+This function is intended for application code written in C. For
+language bindings, see `blake3_hasher_init_derive_key_raw` below.
+
+---
+
+```c
+void blake3_hasher_init_derive_key_raw(
+  blake3_hasher *self,
+  const void *context,
+  size_t context_len);
+```
+
+As `blake3_hasher_init_derive_key` above, except that the context string
+is given as a pointer to an array of arbitrary bytes with a provided
+length. This is intended for writing language bindings, where C string
+conversion would add unnecessary overhead and new error cases. Unicode
+strings should be encoded as UTF-8.
+
+Application code in C should prefer `blake3_hasher_init_derive_key`,
+which takes the context as a C string. If you need to use arbitrary
+bytes as a context string in application code, consider whether you're
+violating the requirement that context strings should be hardcoded.
+
+---
+
+```c
+void blake3_hasher_finalize_seek(
+  const blake3_hasher *self,
+  uint64_t seek,
+  uint8_t *out,
+  size_t out_len);
+```
+
+The same as `blake3_hasher_finalize`, but with an additional `seek`
+parameter for the starting byte position in the output stream. To
+efficiently stream a large output without allocating memory, call this
+function in a loop, incrementing `seek` by the output length each time.
+
+---
+
+```c
+void blake3_hasher_reset(
+  blake3_hasher *self);
+```
+
+Reset the hasher to its initial state, prior to any calls to
+`blake3_hasher_update`. Currently this is no different from calling
+`blake3_hasher_init` or similar again. However, if this implementation gains
+multithreading support in the future, and if `blake3_hasher` holds (optional)
+threading resources, this function will reuse those resources. Until then, this
+is mainly for feature compatibility with the Rust implementation.
+
+
+# Building
+
+This implementation is just C and assembly files. It doesn't include a
+public-facing build system. (The `Makefile` in this directory is only
+for testing.) Instead, the intention is that you can include these files
+in whatever build system you're already using. This section describes
+the commands your build system should execute, or which you can execute
+by hand. Note that these steps may change in future versions.
+
+## x86
+
+Dynamic dispatch is enabled by default on x86. The implementation will
+query the CPU at runtime to detect SIMD support, and it will use the
+widest instruction set available. By default, `blake3_dispatch.c`
+expects to be linked with code for five different instruction sets:
+portable C, SSE2, SSE4.1, AVX2, and AVX-512.
+
+For each of the x86 SIMD instruction sets, four versions are available:
+three flavors of assembly (Unix, Windows MSVC, and Windows GNU) and one
+version using C intrinsics. The assembly versions are generally
+preferred. They perform better, they perform more consistently across
+different compilers, and they build more quickly. On the other hand, the
+assembly versions are x86\_64-only, and you need to select the right
+flavor for your target platform.
+
+Here's an example of building a shared library on x86\_64 Linux using
+the assembly implementations:
+
+```bash
+gcc -shared -O3 -o libblake3.so blake3.c blake3_dispatch.c blake3_portable.c \
+    blake3_sse2_x86-64_unix.S blake3_sse41_x86-64_unix.S blake3_avx2_x86-64_unix.S \
+    blake3_avx512_x86-64_unix.S
+```
+
+When building the intrinsics-based implementations, you need to build
+each implementation separately, with the corresponding instruction set
+explicitly enabled in the compiler. Here's the same shared library using
+the intrinsics-based implementations:
+
+```bash
+gcc -c -fPIC -O3 -msse2 blake3_sse2.c -o blake3_sse2.o
+gcc -c -fPIC -O3 -msse4.1 blake3_sse41.c -o blake3_sse41.o
+gcc -c -fPIC -O3 -mavx2 blake3_avx2.c -o blake3_avx2.o
+gcc -c -fPIC -O3 -mavx512f -mavx512vl blake3_avx512.c -o blake3_avx512.o
+gcc -shared -O3 -o libblake3.so blake3.c blake3_dispatch.c blake3_portable.c \
+    blake3_avx2.o blake3_avx512.o blake3_sse41.o blake3_sse2.o
+```
+
+Note above that building `blake3_avx512.c` requires both `-mavx512f` and
+`-mavx512vl` under GCC and Clang. Under MSVC, the single `/arch:AVX512`
+flag is sufficient. The MSVC equivalent of `-mavx2` is `/arch:AVX2`.
+MSVC enables SSE2 and SSE4.1 by defaut, and it doesn't have a
+corresponding flag.
+
+If you want to omit SIMD code entirely, you need to explicitly disable
+each instruction set. Here's an example of building a shared library on
+x86 with only portable code:
+
+```bash
+gcc -shared -O3 -o libblake3.so -DBLAKE3_NO_SSE2 -DBLAKE3_NO_SSE41 -DBLAKE3_NO_AVX2 \
+    -DBLAKE3_NO_AVX512 blake3.c blake3_dispatch.c blake3_portable.c
+```
+
+## ARM NEON
+
+The NEON implementation is enabled by default on AArch64, but not on
+other ARM targets, since not all of them support it. To enable it, set
+`BLAKE3_USE_NEON=1`. Here's an example of building a shared library on
+ARM Linux with NEON support:
+
+```bash
+gcc -shared -O3 -o libblake3.so -DBLAKE3_USE_NEON=1 blake3.c blake3_dispatch.c \
+    blake3_portable.c blake3_neon.c
+```
+
+To explicitiy disable using NEON instructions on AArch64, set
+`BLAKE3_USE_NEON=0`.
+
+```bash
+gcc -shared -O3 -o libblake3.so -DBLAKE3_USE_NEON=0 blake3.c blake3_dispatch.c \
+    blake3_portable.c 
+```
+
+Note that on some targets (ARMv7 in particular), extra flags may be
+required to activate NEON support in the compiler. If you see an error
+like...
+
+```
+/usr/lib/gcc/armv7l-unknown-linux-gnueabihf/9.2.0/include/arm_neon.h:635:1: error: inlining failed
+in call to always_inline ‘vaddq_u32’: target specific option mismatch
+```
+
+...then you may need to add something like `-mfpu=neon-vfpv4
+-mfloat-abi=hard`.
+
+## Other Platforms
+
+The portable implementation should work on most other architectures. For
+example:
+
+```bash
+gcc -shared -O3 -o libblake3.so blake3.c blake3_dispatch.c blake3_portable.c
+```
+
+# Multithreading
+
+Unlike the Rust implementation, the C implementation doesn't currently support
+multithreading. A future version of this library could add support by taking an
+optional dependency on OpenMP or similar. Alternatively, we could expose a
+lower-level API to allow callers to implement concurrency themselves. The
+former would be more convenient and less error-prone, but the latter would give
+callers the maximum possible amount of control. The best choice here depends on
+the specific use case, so if you have a use case for multithreaded hashing in
+C, please file a GitHub issue and let us know.

llvm/lib/Support/BLAKE3/blake3.h

+#ifndef BLAKE3_H
+#define BLAKE3_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define BLAKE3_VERSION_STRING "1.3.1"
+#define BLAKE3_KEY_LEN 32
+#define BLAKE3_OUT_LEN 32
+#define BLAKE3_BLOCK_LEN 64
+#define BLAKE3_CHUNK_LEN 1024
+#define BLAKE3_MAX_DEPTH 54
+
+// This struct is a private implementation detail. It has to be here because
+// it's part of blake3_hasher below.
+typedef struct {
+  uint32_t cv[8];
+  uint64_t chunk_counter;
+  uint8_t buf[BLAKE3_BLOCK_LEN];
+  uint8_t buf_len;
+  uint8_t blocks_compressed;
+  uint8_t flags;
+} blake3_chunk_state;
+
+typedef struct {
+  uint32_t key[8];
+  blake3_chunk_state chunk;
+  uint8_t cv_stack_len;
+  // 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.
+  uint8_t cv_stack[(BLAKE3_MAX_DEPTH + 1) * BLAKE3_OUT_LEN];
+} blake3_hasher;
+
+const char *blake3_version(void);
+void blake3_hasher_init(blake3_hasher *self);
+void blake3_hasher_init_keyed(blake3_hasher *self,
+                              const uint8_t key[BLAKE3_KEY_LEN]);
+void blake3_hasher_init_derive_key(blake3_hasher *self, const char *context);
+void blake3_hasher_init_derive_key_raw(blake3_hasher *self, const void *context,
+                                       size_t context_len);
+void blake3_hasher_update(blake3_hasher *self, const void *input,
+                          size_t input_len);
+void blake3_hasher_finalize(const blake3_hasher *self, uint8_t *out,
+                            size_t out_len);
+void blake3_hasher_finalize_seek(const blake3_hasher *self, uint64_t seek,
+                                 uint8_t *out, size_t out_len);
+void blake3_hasher_reset(blake3_hasher *self);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* BLAKE3_H */

llvm/lib/Support/BLAKE3/blake3_avx2.c

+#include "blake3_impl.h"
+
+#include <immintrin.h>
+
+#define DEGREE 8
+
+INLINE __m256i loadu(const uint8_t src[32]) {
+  return _mm256_loadu_si256((const __m256i *)src);
+}
+
+INLINE void storeu(__m256i src, uint8_t dest[16]) {
+  _mm256_storeu_si256((__m256i *)dest, src);
+}
+
+INLINE __m256i addv(__m256i a, __m256i b) { return _mm256_add_epi32(a, b); }
+
+// Note that clang-format doesn't like the name "xor" for some reason.
+INLINE __m256i xorv(__m256i a, __m256i b) { return _mm256_xor_si256(a, b); }
+
+INLINE __m256i set1(uint32_t x) { return _mm256_set1_epi32((int32_t)x); }
+
+INLINE __m256i rot16(__m256i x) {
+  return _mm256_shuffle_epi8(
+      x, _mm256_set_epi8(13, 12, 15, 14, 9, 8, 11, 10, 5, 4, 7, 6, 1, 0, 3, 2,
+                         13, 12, 15, 14, 9, 8, 11, 10, 5, 4, 7, 6, 1, 0, 3, 2));
+}
+
+INLINE __m256i rot12(__m256i x) {
+  return _mm256_or_si256(_mm256_srli_epi32(x, 12), _mm256_slli_epi32(x, 32 - 12));
+}
+
+INLINE __m256i rot8(__m256i x) {
+  return _mm256_shuffle_epi8(
+      x, _mm256_set_epi8(12, 15, 14, 13, 8, 11, 10, 9, 4, 7, 6, 5, 0, 3, 2, 1,
+                         12, 15, 14, 13, 8, 11, 10, 9, 4, 7, 6, 5, 0, 3, 2, 1));
+}
+
+INLINE __m256i rot7(__m256i x) {
+  return _mm256_or_si256(_mm256_srli_epi32(x, 7), _mm256_slli_epi32(x, 32 - 7));
+}
+
+INLINE void round_fn(__m256i v[16], __m256i m[16], size_t r) {
+  v[0] = addv(v[0], m[(size_t)MSG_SCHEDULE[r][0]]);
+  v[1] = addv(v[1], m[(size_t)MSG_SCHEDULE[r][2]]);
+  v[2] = addv(v[2], m[(size_t)MSG_SCHEDULE[r][4]]);
+  v[3] = addv(v[3], m[(size_t)MSG_SCHEDULE[r][6]]);
+  v[0] = addv(v[0], v[4]);
+  v[1] = addv(v[1], v[5]);
+  v[2] = addv(v[2], v[6]);
+  v[3] = addv(v[3], v[7]);
+  v[12] = xorv(v[12], v[0]);
+  v[13] = xorv(v[13], v[1]);
+  v[14] = xorv(v[14], v[2]);
+  v[15] = xorv(v[15], v[3]);
+  v[12] = rot16(v[12]);
+  v[13] = rot16(v[13]);
+  v[14] = rot16(v[14]);
+  v[15] = rot16(v[15]);
+  v[8] = addv(v[8], v[12]);
+  v[9] = addv(v[9], v[13]);
+  v[10] = addv(v[10], v[14]);
+  v[11] = addv(v[11], v[15]);
+  v[4] = xorv(v[4], v[8]);
+  v[5] = xorv(v[5], v[9]);
+  v[6] = xorv(v[6], v[10]);
+  v[7] = xorv(v[7], v[11]);
+  v[4] = rot12(v[4]);
+  v[5] = rot12(v[5]);
+  v[6] = rot12(v[6]);
+  v[7] = rot12(v[7]);
+  v[0] = addv(v[0], m[(size_t)MSG_SCHEDULE[r][1]]);
+  v[1] = addv(v[1], m[(size_t)MSG_SCHEDULE[r][3]]);
+  v[2] = addv(v[2], m[(size_t)MSG_SCHEDULE[r][5]]);
+  v[3] = addv(v[3], m[(size_t)MSG_SCHEDULE[r][7]]);
+  v[0] = addv(v[0], v[4]);
+  v[1] = addv(v[1], v[5]);
+  v[2] = addv(v[2], v[6]);
+  v[3] = addv(v[3], v[7]);
+  v[12] = xorv(v[12], v[0]);
+  v[13] = xorv(v[13], v[1]);
+  v[14] = xorv(v[14], v[2]);
+  v[15] = xorv(v[15], v[3]);
+  v[12] = rot8(v[12]);
+  v[13] = rot8(v[13]);
+  v[14] = rot8(v[14]);
+  v[15] = rot8(v[15]);
+  v[8] = addv(v[8], v[12]);
+  v[9] = addv(v[9], v[13]);
+  v[10] = addv(v[10], v[14]);
+  v[11] = addv(v[11], v[15]);
+  v[4] = xorv(v[4], v[8]);
+  v[5] = xorv(v[5], v[9]);
+  v[6] = xorv(v[6], v[10]);
+  v[7] = xorv(v[7], v[11]);
+  v[4] = rot7(v[4]);
+  v[5] = rot7(v[5]);
+  v[6] = rot7(v[6]);
+  v[7] = rot7(v[7]);
+
+  v[0] = addv(v[0], m[(size_t)MSG_SCHEDULE[r][8]]);
+  v[1] = addv(v[1], m[(size_t)MSG_SCHEDULE[r][10]]);
+  v[2] = addv(v[2], m[(size_t)MSG_SCHEDULE[r][12]]);
+  v[3] = addv(v[3], m[(size_t)MSG_SCHEDULE[r][14]]);
+  v[0] = addv(v[0], v[5]);
+  v[1] = addv(v[1], v[6]);
+  v[2] = addv(v[2], v[7]);
+  v[3] = addv(v[3], v[4]);
+  v[15] = xorv(v[15], v[0]);
+  v[12] = xorv(v[12], v[1]);
+  v[13] = xorv(v[13], v[2]);
+  v[14] = xorv(v[14], v[3]);
+  v[15] = rot16(v[15]);
+  v[12] = rot16(v[12]);
+  v[13] = rot16(v[13]);
+  v[14] = rot16(v[14]);
+  v[10] = addv(v[10], v[15]);
+  v[11] = addv(v[11], v[12]);
+  v[8] = addv(v[8], v[13]);
+  v[9] = addv(v[9], v[14]);
+  v[5] = xorv(v[5], v[10]);
+  v[6] = xorv(v[6], v[11]);
+  v[7] = xorv(v[7], v[8]);
+  v[4] = xorv(v[4], v[9]);
+  v[5] = rot12(v[5]);
+  v[6] = rot12(v[6]);
+  v[7] = rot12(v[7]);
+  v[4] = rot12(v[4]);
+  v[0] = addv(v[0], m[(size_t)MSG_SCHEDULE[r][9]]);
+  v[1] = addv(v[1], m[(size_t)MSG_SCHEDULE[r][11]]);
+  v[2] = addv(v[2], m[(size_t)MSG_SCHEDULE[r][13]]);
+  v[3] = addv(v[3], m[(size_t)MSG_SCHEDULE[r][15]]);
+  v[0] = addv(v[0], v[5]);
+  v[1] = addv(v[1], v[6]);
+  v[2] = addv(v[2], v[7]);
+  v[3] = addv(v[3], v[4]);
+  v[15] = xorv(v[15], v[0]);
+  v[12] = xorv(v[12], v[1]);
+  v[13] = xorv(v[13], v[2]);
+  v[14] = xorv(v[14], v[3]);
+  v[15] = rot8(v[15]);
+  v[12] = rot8(v[12]);
+  v[13] = rot8(v[13]);
+  v[14] = rot8(v[14]);
+  v[10] = addv(v[10], v[15]);
+  v[11] = addv(v[11], v[12]);
+  v[8] = addv(v[8], v[13]);
+  v[9] = addv(v[9], v[14]);
+  v[5] = xorv(v[5], v[10]);
+  v[6] = xorv(v[6], v[11]);
+  v[7] = xorv(v[7], v[8]);
+  v[4] = xorv(v[4], v[9]);
+  v[5] = rot7(v[5]);
+  v[6] = rot7(v[6]);
+  v[7] = rot7(v[7]);
+  v[4] = rot7(v[4]);
+}
+
+INLINE void transpose_vecs(__m256i vecs[DEGREE]) {
+  // Interleave 32-bit lanes. The low unpack is lanes 00/11/44/55, and the high
+  // is 22/33/66/77.
+  __m256i ab_0145 = _mm256_unpacklo_epi32(vecs[0], vecs[1]);
+  __m256i ab_2367 = _mm256_unpackhi_epi32(vecs[0], vecs[1]);
+  __m256i cd_0145 = _mm256_unpacklo_epi32(vecs[2], vecs[3]);
+  __m256i cd_2367 = _mm256_unpackhi_epi32(vecs[2], vecs[3]);
+  __m256i ef_0145 = _mm256_unpacklo_epi32(vecs[4], vecs[5]);
+  __m256i ef_2367 = _mm256_unpackhi_epi32(vecs[4], vecs[5]);
+  __m256i gh_0145 = _mm256_unpacklo_epi32(vecs[6], vecs[7]);
+  __m256i gh_2367 = _mm256_unpackhi_epi32(vecs[6], vecs[7]);
+
+  // Interleave 64-bit lates. The low unpack is lanes 00/22 and the high is
+  // 11/33.
+  __m256i abcd_04 = _mm256_unpacklo_epi64(ab_0145, cd_0145);
+  __m256i abcd_15 = _mm256_unpackhi_epi64(ab_0145, cd_0145);
+  __m256i abcd_26 = _mm256_unpacklo_epi64(ab_2367, cd_2367);
+  __m256i abcd_37 = _mm256_unpackhi_epi64(ab_2367, cd_2367);
+  __m256i efgh_04 = _mm256_unpacklo_epi64(ef_0145, gh_0145);
+  __m256i efgh_15 = _mm256_unpackhi_epi64(ef_0145, gh_0145);
+  __m256i efgh_26 = _mm256_unpacklo_epi64(ef_2367, gh_2367);
+  __m256i efgh_37 = _mm256_unpackhi_epi64(ef_2367, gh_2367);
+
+  // Interleave 128-bit lanes.
+  vecs[0] = _mm256_permute2x128_si256(abcd_04, efgh_04, 0x20);
+  vecs[1] = _mm256_permute2x128_si256(abcd_15, efgh_15, 0x20);
+  vecs[2] = _mm256_permute2x128_si256(abcd_26, efgh_26, 0x20);
+  vecs[3] = _mm256_permute2x128_si256(abcd_37, efgh_37, 0x20);
+  vecs[4] = _mm256_permute2x128_si256(abcd_04, efgh_04, 0x31);
+  vecs[5] = _mm256_permute2x128_si256(abcd_15, efgh_15, 0x31);
+  vecs[6] = _mm256_permute2x128_si256(abcd_26, efgh_26, 0x31);
+  vecs[7] = _mm256_permute2x128_si256(abcd_37, efgh_37, 0x31);
+}
+
+INLINE void transpose_msg_vecs(const uint8_t *const *inputs,
+                               size_t block_offset, __m256i out[16]) {
+  out[0] = loadu(&inputs[0][block_offset + 0 * sizeof(__m256i)]);
+  out[1] = loadu(&inputs[1][block_offset + 0 * sizeof(__m256i)]);
+  out[2] = loadu(&inputs[2][block_offset + 0 * sizeof(__m256i)]);
+  out[3] = loadu(&inputs[3][block_offset + 0 * sizeof(__m256i)]);
+  out[4] = loadu(&inputs[4][block_offset + 0 * sizeof(__m256i)]);
+  out[5] = loadu(&inputs[5][block_offset + 0 * sizeof(__m256i)]);
+  out[6] = loadu(&inputs[6][block_offset + 0 * sizeof(__m256i)]);
+  out[7] = loadu(&inputs[7][block_offset + 0 * sizeof(__m256i)]);
+  out[8] = loadu(&inputs[0][block_offset + 1 * sizeof(__m256i)]);
+  out[9] = loadu(&inputs[1][block_offset + 1 * sizeof(__m256i)]);
+  out[10] = loadu(&inputs[2][block_offset + 1 * sizeof(__m256i)]);
+  out[11] = loadu(&inputs[3][block_offset + 1 * sizeof(__m256i)]);
+  out[12] = loadu(&inputs[4][block_offset + 1 * sizeof(__m256i)]);
+  out[13] = loadu(&inputs[5][block_offset + 1 * sizeof(__m256i)]);
+  out[14] = loadu(&inputs[6][block_offset + 1 * sizeof(__m256i)]);
+  out[15] = loadu(&inputs[7][block_offset + 1 * sizeof(__m256i)]);
+  for (size_t i = 0; i < 8; ++i) {
+    _mm_prefetch((const void *)&inputs[i][block_offset + 256], _MM_HINT_T0);
+  }
+  transpose_vecs(&out[0]);
+  transpose_vecs(&out[8]);
+}
+
+INLINE void load_counters(uint64_t counter, bool increment_counter,
+                          __m256i *out_lo, __m256i *out_hi) {
+  const __m256i mask = _mm256_set1_epi32(-(int32_t)increment_counter);
+  const __m256i add0 = _mm256_set_epi32(7, 6, 5, 4, 3, 2, 1, 0);
+  const __m256i add1 = _mm256_and_si256(mask, add0);
+  __m256i l = _mm256_add_epi32(_mm256_set1_epi32((int32_t)counter), add1);
+  __m256i carry = _mm256_cmpgt_epi32(_mm256_xor_si256(add1, _mm256_set1_epi32(0x80000000)), 
+                                     _mm256_xor_si256(   l, _mm256_set1_epi32(0x80000000)));
+  __m256i h = _mm256_sub_epi32(_mm256_set1_epi32((int32_t)(counter >> 32)), carry);
+  *out_lo = l;
+  *out_hi = h;
+}
+
+static
+void blake3_hash8_avx2(const uint8_t *const *inputs, size_t blocks,
+                       const uint32_t key[8], uint64_t counter,
+                       bool increment_counter, uint8_t flags,
+                       uint8_t flags_start, uint8_t flags_end, uint8_t *out) {
+  __m256i h_vecs[8] = {
+      set1(key[0]), set1(key[1]), set1(key[2]), set1(key[3]),
+      set1(key[4]), set1(key[5]), set1(key[6]), set1(key[7]),
+  };
+  __m256i counter_low_vec, counter_high_vec;
+  load_counters(counter, increment_counter, &counter_low_vec,
+                &counter_high_vec);
+  uint8_t block_flags = flags | flags_start;
+
+  for (size_t block = 0; block < blocks; block++) {
+    if (block + 1 == blocks) {
+      block_flags |= flags_end;
+    }
+    __m256i block_len_vec = set1(BLAKE3_BLOCK_LEN);
+    __m256i block_flags_vec = set1(block_flags);
+    __m256i msg_vecs[16];
+    transpose_msg_vecs(inputs, block * BLAKE3_BLOCK_LEN, msg_vecs);
+
+    __m256i v[16] = {
+        h_vecs[0],       h_vecs[1],        h_vecs[2],     h_vecs[3],
+        h_vecs[4],       h_vecs[5],        h_vecs[6],     h_vecs[7],
+        set1(IV[0]),     set1(IV[1]),      set1(IV[2]),   set1(IV[3]),
+        counter_low_vec, counter_high_vec, block_len_vec, block_flags_vec,
+    };
+    round_fn(v, msg_vecs, 0);
+    round_fn(v, msg_vecs, 1);
+    round_fn(v, msg_vecs, 2);
+    round_fn(v, msg_vecs, 3);
+    round_fn(v, msg_vecs, 4);
+    round_fn(v, msg_vecs, 5);
+    round_fn(v, msg_vecs, 6);
+    h_vecs[0] = xorv(v[0], v[8]);
+    h_vecs[1] = xorv(v[1], v[9]);
+    h_vecs[2] = xorv(v[2], v[10]);
+    h_vecs[3] = xorv(v[3], v[11]);
+    h_vecs[4] = xorv(v[4], v[12]);
+    h_vecs[5] = xorv(v[5], v[13]);
+    h_vecs[6] = xorv(v[6], v[14]);
+    h_vecs[7] = xorv(v[7], v[15]);
+
+    block_flags = flags;
+  }
+
+  transpose_vecs(h_vecs);
+  storeu(h_vecs[0], &out[0 * sizeof(__m256i)]);
+  storeu(h_vecs[1], &out[1 * sizeof(__m256i)]);
+  storeu(h_vecs[2], &out[2 * sizeof(__m256i)]);
+  storeu(h_vecs[3], &out[3 * sizeof(__m256i)]);
+  storeu(h_vecs[4], &out[4 * sizeof(__m256i)]);
+  storeu(h_vecs[5], &out[5 * sizeof(__m256i)]);
+  storeu(h_vecs[6], &out[6 * sizeof(__m256i)]);
+  storeu(h_vecs[7], &out[7 * sizeof(__m256i)]);
+}
+
+#if !defined(BLAKE3_NO_SSE41)
+void blake3_hash_many_sse41(const uint8_t *const *inputs, size_t num_inputs,
+                            size_t blocks, const uint32_t key[8],
+                            uint64_t counter, bool increment_counter,
+                            uint8_t flags, uint8_t flags_start,
+                            uint8_t flags_end, uint8_t *out);
+#else
+void blake3_hash_many_portable(const uint8_t *const *inputs, size_t num_inputs,
+                               size_t blocks, const uint32_t key[8],
+                               uint64_t counter, bool increment_counter,
+                               uint8_t flags, uint8_t flags_start,
+                               uint8_t flags_end, uint8_t *out);
+#endif
+
+void blake3_hash_many_avx2(const uint8_t *const *inputs, size_t num_inputs,
+                           size_t blocks, const uint32_t key[8],
+                           uint64_t counter, bool increment_counter,
+                           uint8_t flags, uint8_t flags_start,
+                           uint8_t flags_end, uint8_t *out) {
+  while (num_inputs >= DEGREE) {
+    blake3_hash8_avx2(inputs, blocks, key, counter, increment_counter, flags,
+                      flags_start, flags_end, out);
+    if (increment_counter) {
+      counter += DEGREE;
+    }
+    inputs += DEGREE;
+    num_inputs -= DEGREE;
+    out = &out[DEGREE * BLAKE3_OUT_LEN];
+  }
+#if !defined(BLAKE3_NO_SSE41)
+  blake3_hash_many_sse41(inputs, num_inputs, blocks, key, counter,
+                         increment_counter, flags, flags_start, flags_end, out);
+#else
+  blake3_hash_many_portable(inputs, num_inputs, blocks, key, counter,
+                            increment_counter, flags, flags_start, flags_end,
+                            out);
+#endif
+}