# sha256-simd

Accelerate SHA256 computations in pure Go using AVX512, SHA Extensions for x86
and ARM64 for ARM.
On AVX512 it provides an up to 8x improvement (over 3 GB/s per core).
SHA Extensions give a performance boost of close to 4x over native.

## Introduction

This package is designed as a replacement for `crypto/sha256`.
For ARM CPUs with the Cryptography Extensions, advantage is taken of the SHA2
instructions resulting in a massive performance improvement.

This package uses Golang assembly.
The AVX512 version is based on the Intel's "multi-buffer crypto library for
IPSec" whereas the other Intel implementations are described in "Fast SHA-256
Implementations on Intel Architecture Processors" by J. Guilford et al.

## Support for Intel SHA Extensions

Support for the Intel SHA Extensions has been added by Kristofer Peterson (
@svenski123), originally developed for
spacemeshos [here](https://github.com/spacemeshos/POET/issues/23). On CPUs that
support it (known thus far Intel Celeron J3455 and AMD Ryzen) it gives a
significant boost in performance (with thanks to @AudriusButkevicius for
reporting the results; full
results [here](https://github.com/minio/sha256-simd/pull/37#issuecomment-451607827)).

```
$ benchcmp avx2.txt sha-ext.txt
benchmark           AVX2 MB/s    SHA Ext MB/s  speedup
BenchmarkHash5M     514.40       1975.17       3.84x
```

Thanks to Kristofer Peterson, we also added additional performance changes such
as optimized padding,
endian conversions which sped up all implementations i.e. Intel SHA alone while
doubled performance for small sizes,
the other changes increased everything roughly 50%.

## Support for AVX512

We have added support for AVX512 which results in an up to 8x performance
improvement over AVX2 (3.0 GHz Xeon Platinum 8124M CPU):

```
$ benchcmp avx2.txt avx512.txt
benchmark           AVX2 MB/s    AVX512 MB/s  speedup
BenchmarkHash5M     448.62       3498.20      7.80x
```

The original code was developed by Intel as part of
the [multi-buffer crypto library](https://github.com/intel/intel-ipsec-mb) for
IPSec or more specifically
this [AVX512](https://github.com/intel/intel-ipsec-mb/blob/master/avx512/sha256_x16_avx512.asm)
implementation. The key idea behind it is to process a total of 16 checksums in
parallel by “transposing” 16 (independent) messages of 64 bytes between a total
of 16 ZMM registers (each 64 bytes wide).

Transposing the input messages means that in order to take full advantage of the
speedup you need to have a (server) workload where multiple threads are doing
SHA256 calculations in parallel. Unfortunately for this algorithm it is not
possible for two message blocks processed in parallel to be dependent on one
another — because then the (interim) result of the first part of the message has
to be an input into the processing of the second part of the message.

Whereas the original Intel C implementation requires some sort of explicit
scheduling of messages to be processed in parallel, for Golang it makes sense to
take advantage of channels in order to group messages together and use channels
as well for sending back the results (thereby effectively decoupling the
calculations). We have implemented a fairly simple scheduling mechanism that
seems to work well in practice.

Due to this different way of scheduling, we decided to use an explicit method to
instantiate the AVX512 version. Essentially one or more AVX512 processing
servers ([
`Avx512Server`](https://github.com/minio/sha256-simd/blob/master/sha256blockAvx512_amd64.go#L294))
have to be created whereby each server can hash over 3 GB/s on a single core. An
`hash.Hash` object ([
`Avx512Digest`](https://github.com/minio/sha256-simd/blob/master/sha256blockAvx512_amd64.go#L45))
is then instantiated using one of these servers and used in the regular fashion:

```go
import "mleku.dev/pkg/sha256"

func main() {
	server := sha256.NewAvx512Server()
	h512 := sha256.NewAvx512(server)
	h512.Write(fileBlock)
	digest := h512.Sum([]byte{})
}
```

Note that, because of the scheduling overhead, for small messages (< 1 MB) you
will be better off using the regular SHA256 hashing (but those are typically not
performance critical anyway). Some other tips to get the best performance:

- Have many go routines doing SHA256 calculations in parallel.
- Try to Write() messages in multiples of 64 bytes.
- Try to keep the overall length of messages to a roughly similar size ie. 5
  MB (this way all 16 ‘lanes’ in the AVX512 computations are contributing as
  much as possible).

More detailed information can be found in
this [blog](https://blog.minio.io/accelerate-sha256-up-to-8x-over-3-gb-s-per-core-with-avx512-a0b1d64f78f)
post including scaling across cores.

## Drop-In Replacement

The following code snippet shows how you can use `github.com/minio/sha256-simd`.
This will automatically select the fastest method for the architecture on which
it will be executed.

```go
import "crypto.orly/sha256"

func main() {
        ...
	shaWriter := sha256.New()
	io.Copy(shaWriter, file)
        ...
}
```

## Performance

Below is the speed in MB/s for a single core (ranked fast to slow) for blocks
larger than 1 MB.

| Processor                         | SIMD    | Speed (MB/s) |
| --------------------------------- | ------- | -----------: |
| 3.0 GHz Intel Xeon Platinum 8124M | AVX512  |         3498 |
| 3.7 GHz AMD Ryzen 7 2700X         | SHA Ext |         1979 |
| 1.2 GHz ARM Cortex-A53            | ARM64   |          638 |

## asm2plan9s

In order to be able to work more easily with AVX512/AVX2 instructions, a
separate tool was developed to convert SIMD instructions into the corresponding
BYTE sequence as accepted by Go assembly.
See [asm2plan9s](https://github.com/minio/asm2plan9s) for more information.

## Why and benefits

One of the most performance sensitive parts of
the [Minio](https://github.com/minio/minio) object storage server is related to
SHA256 hash sums calculations. For instance during multi part uploads each part
that is uploaded needs to be verified for data integrity by the server.

Other applications that can benefit from enhanced SHA256 performance are
deduplication in storage systems, intrusion detection, version control systems,
integrity checking, etc.

## ARM SHA Extensions

The 64-bit ARMv8 core has introduced new instructions for SHA1 and SHA2
acceleration as part of
the [Cryptography Extensions](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0501f/CHDFJBCJ.html).
Below you can see a small excerpt highlighting one of the rounds as is done for
the SHA256 calculation process (for full code
see [sha256block_arm64.s](https://github.com/minio/sha256-simd/blob/master/sha256block_arm64.s)).

```
sha256h    q2, q3, v9.4s
sha256h2   q3, q4, v9.4s
sha256su0  v5.4s, v6.4s
rev32      v8.16b, v8.16b
add        v9.4s, v7.4s, v18.4s
mov        v4.16b, v2.16b
sha256h    q2, q3, v10.4s
sha256h2   q3, q4, v10.4s
sha256su0  v6.4s, v7.4s
sha256su1  v5.4s, v7.4s, v8.4s
```

### Detailed benchmarks

Benchmarks generated on a 1.2 Ghz Quad-Core ARM Cortex A53
equipped [Pine64](https://www.pine64.com/).

```
minio@minio-arm:$ benchcmp golang.txt arm64.txt
benchmark                 golang         arm64        speedup
BenchmarkHash8Bytes-4     0.68 MB/s      5.70 MB/s      8.38x
BenchmarkHash1K-4         5.65 MB/s    326.30 MB/s     57.75x
BenchmarkHash8K-4         6.00 MB/s    570.63 MB/s     95.11x
BenchmarkHash1M-4         6.05 MB/s    638.23 MB/s    105.49x
```

## License

Released under the Apache License v2.0. You can find the complete text in the
file LICENSE.

## Contributing

Contributions are welcome, please send PRs for any enhancements.
