reed-solomon-simd 3.0.1

Reed-Solomon coding with O(n log n) complexity. Leverages SIMD instructions on x86(-64) and AArch64.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227

# reed-solomon-simd

Reed-Solomon erasure coding based on [Leopard-RS], featuring:

- `O(n log n)` complexity.
- Entirely written in Rust.
- Runtime selection of best SIMD implementation on both AArch64 (Neon) and x86(-64) (SSSE3 and AVX2) with
fallback to plain Rust.
- Any combination of 1 - 32768 original shards with 1 - 32768 recovery shards.
- Up to 65535 original or recovery shards is also possible with following limitations:

| `original_count` | `recovery_count` |
| ---------------- | ---------------- |
| `<= 2^16 - 2^n`  | `<= 2^n`         |
| `<= 61440`       | `<= 4096`        |
| `<= 57344`       | `<= 8192`        |
| `<= 49152`       | `<= 16384`       |
| **`<= 32768`**   | **`<= 32768`**   |
| `<= 16384`       | `<= 49152`       |
| `<= 8192`        | `<= 57344`       |
| `<= 4096`        | `<= 61440`       |
| `<= 2^n`         | `<= 2^16 - 2^n`  |


## Benchmarks

| Original : Recovery | Encode       | Decode (1% loss; 100% loss) |
| ------------------- | ------------ | --------------------------- |
| 32: 32              | 10.237 GiB/s | 254.24 MiB/s ; 253.60 MiB/s |
| 64: 64              | 8.6758 GiB/s | 459.18 MiB/s ; 456.83 MiB/s |
| 128 : 128           | 7.3891 GiB/s | 753.11 MiB/s ; 758.65 MiB/s |
| 256 : 256           | 6.3753 GiB/s | 1.0391 GiB/s ; 1.0323 GiB/s |
| 512 : 512           | 5.5076 GiB/s | 1.1862 GiB/s ; 1.2542 GiB/s |
| 1024 : 1024         | 4.8495 GiB/s | 1.3017 GiB/s ; 1.4178 GiB/s |
| 2048 : 2048         | 4.3733 GiB/s | 1.3341 GiB/s ; 1.4640 GiB/s |
| 4096 : 4096         | 3.9926 GiB/s | 1.2008 GiB/s ; 1.3585 GiB/s |
| 8192 : 8192         | 3.1220 GiB/s | 942.68 MiB/s ; 1012.5 MiB/s |
| 16384 : 16384       | 2.2468 GiB/s | 701.36 MiB/s ; 687.75 MiB/s |
| 32 768 : 32 768     | 1.6049 GiB/s | 681.39 MiB/s ; 667.93 MiB/s |
| 128 : 1 024         | 6.4068 GiB/s | 857.36 MiB/s ; 856.25 MiB/s |
| 1 000 : 100         | 5.6079 GiB/s | 1021.7 MiB/s ; 1022.0 MiB/s |
| 1 000 : 10 000      | 4.0041 GiB/s | 1012.7 MiB/s ; 1014.9 MiB/s |
| 8 192 : 57 344      | 2.3174 GiB/s | 706.97 MiB/s ; 704.85 MiB/s |
| 10 000 : 1 000      | 2.9598 GiB/s | 924.42 MiB/s ; 942.26 MiB/s |
| 57 344 : 8 192      | 1.8894 GiB/s | 657.89 MiB/s ; 664.97 MiB/s |

- Single core AVX2 on an AMD Ryzen 5 3600 (Zen 2, 2019).
- On an Apple Silicon M1 CPU throughput is about the same (+-10%).
- MiB/s and GiB/s are w.r.t the total amount of data,
  i.e. original shards + recovery shards.
    - For decoder this includes missing shards.
- Shards are 1024 bytes.
- Encode benchmark
    - Includes [`add_original_shard`][RSE::add_original_shard] and
      [`encode`][RSE::encode] of [`ReedSolomonEncoder`].
- Decode benchmark
    - Has two MiB/s values for 1% and 100% original shard loss, of maximum possible.
    - Provides minimum required amount of shards to decoder.
    - Includes [`add_original_shard`][RSD::add_original_shard],
      [`add_recovery_shard`][RSD::add_recovery_shard] and
      [`decode`][RSD::decode] of [`ReedSolomonDecoder`].


I invite you to clone [reed-solomon-simd] and run your own benchmark:
```sh
$ cargo bench main
```

## Simple usage

1. Divide data into equal-sized original shards.
   Shard size must be even (`shard.len() % 2 == 0`).
2. Decide how many recovery shards you want.
3. Generate recovery shards with [`reed_solomon_simd::encode`].
4. When some original shards get lost, restore them with [`reed_solomon_simd::decode`].
    - You must provide at least as many shards as there were original shards in total,
      in any combination of original shards and recovery shards.

Note: This crate does not detect or correct errors within a shard. So if data corruption is a likely scenario, you should include an error detection hash with each shard, and skip feeding the corrupted shards to the decoder. Here are a few suggestions for very fast error detection hashes: CRC32c (4 bytes), HighwayHash (8, 16 or 32 bytes) or xxHash (4, 8 or 16 bytes).

### Example

Divide data into 3 original shards of 64 bytes each and generate 5 recovery shards.
Assume then that original shards #0 and #2 are lost
and restore them by providing 1 original shard and 2 recovery shards.

```rust
let original = [
    b"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do ",
    b"eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut e",
    b"nim ad minim veniam, quis nostrud exercitation ullamco laboris n",
];

let recovery = reed_solomon_simd::encode(
    3, // total number of original shards
    5, // total number of recovery shards
    original, // all original shards
)?;

let restored = reed_solomon_simd::decode(
    3, // total number of original shards
    5, // total number of recovery shards
    [  // provided original shards with indexes
        (1, &original[1]),
    ],
    [  // provided recovery shards with indexes
        (1, &recovery[1]),
        (4, &recovery[4]),
    ],
)?;

assert_eq!(restored[&0], original[0]);
assert_eq!(restored[&2], original[2]);
# Ok::<(), reed_solomon_simd::Error>(())
```

## Basic usage

[`ReedSolomonEncoder`] and [`ReedSolomonDecoder`] give more control
of the encoding/decoding process.

Here's the above example using these instead:

```rust
use reed_solomon_simd::{ReedSolomonDecoder, ReedSolomonEncoder};
use std::collections::HashMap;

let original = [
    b"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do ",
    b"eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut e",
    b"nim ad minim veniam, quis nostrud exercitation ullamco laboris n",
];

let mut encoder = ReedSolomonEncoder::new(
    3, // total number of original shards
    5, // total number of recovery shards
    64, // shard size in bytes
)?;

for shard in original {
    encoder.add_original_shard(shard)?;
}

let result = encoder.encode()?;
let recovery: Vec<_> = result.recovery_iter().collect();

let mut decoder = ReedSolomonDecoder::new(
    3, // total number of original shards
    5, // total number of recovery shards
    64, // shard size in bytes
)?;

decoder.add_original_shard(1, original[1])?;
decoder.add_recovery_shard(1, recovery[1])?;
decoder.add_recovery_shard(4, recovery[4])?;

let result = decoder.decode()?;
let restored: HashMap<_, _> = result.restored_original_iter().collect();

assert_eq!(restored[&0], original[0]);
assert_eq!(restored[&2], original[2]);
# Ok::<(), reed_solomon_simd::Error>(())
```

## Advanced usage

See [`rate`][mod:rate] module for advanced encoding/decoding
using chosen [`Engine`] and [`Rate`].

## Benchmarks against other crates

Use `cargo run --release --example quick-comparison`
to run few simple benchmarks against [`reed-solomon-16`], [`reed-solomon-erasure`], [`reed-solomon-novelpoly`] and [`leopard-codec`] crates.

This crate is the fastest in all cases on my AMD Ryzen 5 3600, except in the
case of decoding with about 42 or fewer recovery shards.
There's also a one-time initialization (< 10 ms) for computing tables
which can dominate at really small data amounts.

[`reed-solomon-16`]: https://crates.io/crates/reed-solomon-16
[`reed-solomon-erasure`]: https://crates.io/crates/reed-solomon-erasure
[`reed-solomon-novelpoly`]: https://crates.io/crates/reed-solomon-novelpoly
[`leopard-codec`]: https://crates.io/crates/leopard-codec

## Running tests

Some larger tests are marked `#[ignore]` and are not run with `cargo test`.
Use `cargo test -- --ignored` to run those.

## Safety

The only use of `unsafe` in this crate is to allow for target specific optimizations in [`Ssse3`], [`Avx2`] and [`Neon`].

## Compatibility

Starting from version 3.0.0, shard sizes that are not multiples of 64 are supported. However, if your shard size is a multiple of 64, it remains compatible across all versions.

## Credits

This crate is a fork Markus Laire's [`reed-solomon-16`] crate, which in turn
is based on [Leopard-RS] by Christopher A. Taylor.

[Leopard-RS]: https://github.com/catid/leopard
[reed-solomon-simd]: https://github.com/AndersTrier/reed-solomon-simd

[`Naive`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/engine/struct.Naive.html
[`NoSimd`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/engine/struct.NoSimd.html
[`Ssse3`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/engine/struct.Ssse3.html
[`Avx2`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/engine/struct.Avx2.html
[`Neon`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/engine/struct.Neon.html

[`ReedSolomonEncoder`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonEncoder.html
[RSE::add_original_shard]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonEncoder.html#method.add_original_shard
[RSE::encode]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonEncoder.html#method.encode

[`ReedSolomonDecoder`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonDecoder.html
[RSD::add_original_shard]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonDecoder.html#method.add_original_shard
[RSD::add_recovery_shard]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonDecoder.html#method.add_recovery_shard
[RSD::decode]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/struct.ReedSolomonDecoder.html#method.decode

[`Engine`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/engine/trait.Engine.html
[`Rate`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/rate/trait.Rate.html

[mod:rate]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/rate/index.html

[`reed_solomon_simd::encode`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/fn.encode.html
[`reed_solomon_simd::decode`]: https://docs.rs/reed-solomon-simd/3.0.1/reed_solomon_simd/fn.decode.html