memspan 0.1.0

SIMD-accelerated byte-class scanning for lexers and parsers. Backends: AVX-512, AVX2, SSE4.1, NEON, WASM SIMD128. no_std compatible.
Documentation 
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<div align="center">
<h1>memspan</h1>
</div>
<div align="center">

SIMD-accelerated byte-class scanning for lexers and parsers.

[<img alt="github" src="https://img.shields.io/badge/github-al8n/memspan-8da0cb?style=for-the-badge&logo=Github" height="22">][Github-url]
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English | [简体中文][zh-cn-url]

</div>

## Quick start

```rust
let src = b"   hello, world";

// Skip leading whitespace — dispatches to AVX2 / NEON / SIMD128 at runtime.
let n = memspan::skip_whitespace(src);
assert_eq!(n, 3);

// Find the first comma.
let comma = memspan::skip_until(src, b',');
assert_eq!(comma, Some(8));
```

## Overview

`memspan` provides zero-allocation, `no_std`-compatible functions to skip,
count, and locate bytes in ASCII character classes, dispatching to the best
available SIMD backend at runtime:

| Architecture | Dispatch order |
|---|---|
| x86\_64 | AVX-512BW → AVX2 → SSE4.2 → scalar |
| x86 | SSE4.2 → scalar |
| aarch64 | NEON → scalar |
| wasm32 | SIMD128 → scalar |
| other | scalar |

## Installation

```toml
[dependencies]
memspan = "0.1"
```

For `no_std` without an allocator:

```toml
[dependencies]
memspan = { version = "0.1", default-features = false }
```

## Built-in classes

All class functions return the byte length of the longest matching prefix.

| Function | Matches |
|---|---|
| `skip_whitespace` | ` `, `\t`, `\r`, `\n` |
| `skip_digits` | `0`–`9` |
| `skip_hex_digits` | `0`–`9`, `a`–`f`, `A`–`F` |
| `skip_octal_digits` | `0`–`7` |
| `skip_binary` | `0`, `1` |
| `skip_alpha` | `a`–`z`, `A`–`Z` |
| `skip_alphanumeric` | `a`–`z`, `A`–`Z`, `0`–`9` |
| `skip_ident_start` | `a`–`z`, `A`–`Z`, `_` |
| `skip_ident` | `a`–`z`, `A`–`Z`, `0`–`9`, `_` |
| `skip_lower` | `a`–`z` |
| `skip_upper` | `A`–`Z` |
| `skip_ascii` | `0x00`–`0x7F` |
| `skip_non_ascii` | `0x80`–`0xFF` |
| `skip_ascii_graphic` | `0x21`–`0x7E` (printable non-space) |
| `skip_ascii_control` | `0x00`–`0x1F`, `0x7F` |

## Generic operations

`skip_while`, `skip_until`, `count_matches`, and `find_last` accept any
[`Needles`] value — a single `u8`, a fixed-size array `[u8; N]`, or a `&[u8]`
slice:

```rust
// Skip while any of several bytes match.
let n = memspan::skip_while(b"  ,\t ok", [b' ', b',', b'\t']);
assert_eq!(n, 5);

// Find the first occurrence of any needle — like memchr but multi-byte.
let pos = memspan::skip_until(b"hello\nworld", b'\n');
assert_eq!(pos, Some(5));

// Count every newline in a buffer.
let lines = memspan::count_matches(b"a\nb\nc\n", b'\n');
assert_eq!(lines, 3);

// Find the rightmost match.
let last = memspan::find_last(b"\"hello\"", b'"');
assert_eq!(last, Some(6));
```

## Custom classes with `skip_class!`

Define your own byte class and get the same SIMD dispatch as the built-ins:

```rust
memspan::skip_class! {
    /// Skip whitespace and commas.
    pub fn skip_ws_and_comma(bytes = [b' ', b'\t', b'\r', b'\n', b',']);
}

memspan::skip_class! {
    /// Skip lowercase ASCII letters.
    pub fn skip_lowercase(ranges = [b'a'..=b'z']);
}

memspan::skip_class! {
    /// Skip alphanumeric plus common punctuation.
    pub fn skip_punct_ident(
        bytes  = [b'_', b'-', b'!', b'?'],
        ranges = [b'a'..=b'z', b'A'..=b'Z', b'0'..=b'9'],
    );
}

assert_eq!(skip_ws_and_comma(b"  , ok"), 4);
assert_eq!(skip_lowercase(b"abcXYZ"), 3);
assert_eq!(skip_punct_ident(b"hello-world! 42"), 12);
```

## Benchmarks

Throughput in GiB/s across input sizes, measured on GitHub Actions runners (2026-04-22, `--quick` Criterion runs).
Environments: aarch64 — macOS-latest (ARM64, NEON); x86\_64 — ubuntu-latest (X64, runtime AVX2 detection).

### aarch64 — NEON

| Function | 16 B | 32 B | 64 B | 256 B | 4 KiB | 64 KiB |
|---|---:|---:|---:|---:|---:|---:|
| `skip_binary` | 1.9 | 7.0 | 10.9 | 23.1 | 39.5 | 34.9 |
| `skip_octal_digits` | 2.2 | 7.3 | 12.3 | 27.5 | 41.0 | 45.9 |
| `skip_digits` | 2.2 | 7.3 | 10.6 | 26.7 | 39.9 | 44.8 |
| `skip_hex_digits` | 1.8 | 4.1 | 6.4 | 14.8 | 21.8 | 23.5 |
| `skip_alpha` | 2.3 | 5.8 | 10.4 | 23.1 | 32.6 | 37.6 |
| `skip_alphanumeric` | 1.8 | 4.3 | 6.8 | 14.9 | 19.7 | 23.1 |
| `skip_ident_start` | 1.5 | 3.4 | 6.1 | 12.5 | 24.4 | 23.3 |
| `skip_ident` | 1.3 | 3.8 | 5.6 | 13.2 | 16.6 | 17.8 |
| `skip_whitespace` | 1.9 | 4.5 | 7.0 | 15.2 | 20.2 | 19.0 |

### aarch64 — scalar fallback

| Function | 16 B | 32 B | 64 B | 256 B | 4 KiB | 64 KiB |
|---|---:|---:|---:|---:|---:|---:|
| `skip_binary` | 2.3 | 2.1 | 1.9 | 1.8 | 2.0 | 2.0 |
| `skip_octal_digits` | 1.7 | 2.2 | 2.0 | 1.9 | 2.1 | 2.1 |
| `skip_digits` | 1.9 | 2.3 | 2.2 | 2.3 | 2.4 | 2.2 |
| `skip_hex_digits` | 1.7 | 1.4 | 1.5 | 1.5 | 1.2 | 1.3 |
| `skip_alpha` | 2.3 | 2.5 | 2.2 | 1.9 | 1.9 | 1.9 |
| `skip_alphanumeric` | 1.8 | 1.8 | 1.7 | 1.5 | 1.6 | 1.6 |
| `skip_ident_start` | 1.9 | 1.9 | 1.9 | 1.7 | 1.9 | 2.0 |
| `skip_ident` | 1.5 | 1.6 | 1.5 | 1.5 | 1.6 | 1.6 |
| `skip_whitespace` | 1.4 | 1.6 | 1.8 | 1.6 | 1.8 | 1.8 |

### x86\_64 — AVX2

| Function | 16 B | 32 B | 64 B | 256 B | 4 KiB | 64 KiB |
|---|---:|---:|---:|---:|---:|---:|
| `skip_binary` | 2.0 | 2.5 | 4.7 | 15.8 | 60.7 | 88.4 |
| `skip_octal_digits` | 2.0 | 2.5 | 4.7 | 16.3 | 62.3 | 62.8 |
| `skip_digits` | 2.0 | 2.5 | 4.7 | 16.3 | 63.2 | 80.9 |
| `skip_hex_digits` | 1.4 | 1.7 | 3.1 | 10.3 | 33.2 | 38.3 |
| `skip_alpha` | 2.0 | 2.5 | 4.3 | 14.6 | 59.9 | 68.6 |
| `skip_alphanumeric` | 1.5 | 1.7 | 3.2 | 10.6 | 31.6 | 37.5 |
| `skip_ident_start` | 1.5 | 1.7 | 3.3 | 11.1 | 39.7 | 46.3 |
| `skip_ident` | 1.8 | 1.6 | 2.9 | 9.9 | 28.4 | 33.8 |
| `skip_whitespace` | 1.9 | 2.5 | 4.4 | 13.7 | 38.2 | 46.5 |

### x86\_64 — scalar fallback

| Function | 16 B | 32 B | 64 B | 256 B | 4 KiB | 64 KiB |
|---|---:|---:|---:|---:|---:|---:|
| `skip_binary` | 2.3 | 2.5 | 2.1 | 2.7 | 3.0 | 3.0 |
| `skip_octal_digits` | 2.2 | 2.4 | 2.1 | 2.6 | 3.0 | 3.0 |
| `skip_digits` | 2.1 | 2.5 | 2.1 | 2.7 | 3.0 | 3.0 |
| `skip_hex_digits` | 1.4 | 1.5 | 1.2 | 1.4 | 1.5 | 1.5 |
| `skip_alpha` | 2.1 | 1.8 | 1.8 | 1.7 | 1.8 | 1.8 |
| `skip_alphanumeric` | 1.3 | 1.4 | 1.2 | 1.4 | 1.5 | 1.5 |
| `skip_ident_start` | 1.3 | 1.4 | 1.2 | 1.4 | 1.5 | 1.5 |
| `skip_ident` | 1.3 | 1.4 | 1.3 | 1.4 | 1.5 | 1.5 |
| `skip_whitespace` | 1.8 | 1.5 | 1.3 | 1.9 | 2.0 | 2.0 |

### Generic dispatch (`skip_until` / `skip_while`)

| Function | Backend | 16 B | 32 B | 64 B | 256 B | 4 KiB | 64 KiB |
|---|---|---:|---:|---:|---:|---:|---:|
| `skip_until` | aarch64 NEON | 0.5 | 1.1 | 2.5 | 7.1 | 15.5 | 17.0 |
| `skip_until` | aarch64 scalar | 1.4 | 1.6 | 1.5 | 1.4 | 1.6 | 1.6 |
| `skip_until` | x86\_64 AVX2 | 0.5 | 0.7 | 1.3 | 4.9 | 25.8 | 36.9 |
| `skip_until` | x86\_64 scalar | 0.9 | 0.9 | 0.9 | 1.0 | 1.0 | 1.0 |
| `skip_while` | aarch64 NEON | 0.7 | 1.5 | 3.0 | 8.6 | 16.3 | 16.7 |
| `skip_while` | aarch64 scalar | 1.7 | 1.9 | 2.0 | 1.9 | 2.0 | 2.1 |
| `skip_while` | x86\_64 AVX2 | 0.7 | 0.8 | 1.4 | 5.2 | 26.6 | 37.1 |
| `skip_while` | x86\_64 scalar | 1.1 | 1.1 | 1.0 | 1.1 | 1.2 | 1.2 |

### `skip_class!` macro vs `skip_while`

| | Backend | 16 B | 32 B | 64 B | 256 B | 4 KiB | 64 KiB |
|---|---|---:|---:|---:|---:|---:|---:|
| `skip_class!` macro | aarch64 NEON | 2.0 | 4.4 | 6.9 | 13.5 | 16.7 | 18.2 |
| `skip_while` (array) | aarch64 NEON | 0.7 | 1.4 | 3.0 | 8.8 | 15.1 | 17.6 |
| `skip_class!` macro | x86\_64 AVX2 | 1.7 | 2.4 | 4.3 | 13.6 | 35.8 | 41.7 |
| `skip_while` (array) | x86\_64 AVX2 | 0.7 | 0.8 | 1.4 | 5.2 | 26.4 | 37.8 |

## Features

| Feature | Default | Description |
|---|---|---|
| `std` | ✓ | Link against the standard library |
| `alloc` | | Enable heap allocation without `std` |
| _(neither)_ | | Pure `no_std` / `no_alloc` |

#### License

`memspan` is dual-licensed under the MIT license and the Apache License (Version 2.0).

See [LICENSE-APACHE](LICENSE-APACHE), [LICENSE-MIT](LICENSE-MIT) for details.

Copyright (c) 2026 Al Liu.

[Github-url]: https://github.com/al8n/memspan/
[CI-url]: https://github.com/al8n/memspan/actions/workflows/ci.yml
[doc-url]: https://docs.rs/memspan
[crates-url]: https://crates.io/crates/memspan
[codecov-url]: https://app.codecov.io/gh/al8n/memspan/
[zh-cn-url]: https://github.com/al8n/memspan/tree/main/README-zh_CN.md