coregex

High-performance regex engine for Go. Drop-in replacement for regexp with 3-3000x speedup.*

_{* Typical speedup 15-240x on real-world patterns. 1000x+ achieved on specific edge cases where prefilters skip entire input (e.g., IP pattern on text with no digits).}

Why coregex?

Go's stdlib regexp is intentionally simple — single NFA engine, no optimizations. This guarantees O(n) time but leaves performance on the table.

coregex brings Rust regex-crate architecture to Go:

• Multi-engine: 17 strategies — Lazy DFA, PikeVM, OnePass, BoundedBacktracker, and more
• SIMD prefilters: AVX2/SSSE3 for fast candidate rejection
• Reverse search: Suffix/inner literal patterns run 1000x+ faster
• O(n) guarantee: No backtracking, no ReDoS vulnerabilities

Installation

go get github.com/coregx/coregex

Requires Go 1.25+. Minimal dependencies (golang.org/x/sys, github.com/coregx/ahocorasick).

Quick Start

package main

import (
    "fmt"
    "github.com/coregx/coregex"
)

func main() {
    re := coregex.MustCompile(`\w+@\w+\.\w+`)

    text := []byte("Contact [email protected] for help")

    // Find first match
    fmt.Printf("Found: %s\n", re.Find(text))

    // Check if matches (zero allocation)
    if re.MatchString("[email protected]") {
        fmt.Println("Valid email format")
    }
}

Performance

Cross-language benchmarks on 6MB input, AMD EPYC (source):

Pattern	Go stdlib	coregex	Rust regex	vs stdlib	vs Rust
Literal alternation	554 ms	4.5 ms	0.72 ms	122x	6.2x slower
Multi-literal	1572 ms	12.4 ms	5.5 ms	126x	2.2x slower
Inner .*keyword.*	238 ms	0.27 ms	0.33 ms	881x	1.2x faster
Suffix .*\.txt	239 ms	1.9 ms	1.2 ms	125x	1.5x slower
Multiline (?m)^/.*\.php	102 ms	0.34 ms	0.75 ms	299x	2.2x faster
Email validation	257 ms	0.46 ms	0.31 ms	557x	1.4x slower
URL extraction	256 ms	0.62 ms	0.37 ms	413x	1.6x slower
IP address	494 ms	0.72 ms	13.5 ms	685x	18.8x faster
Version \d+.\d+.\d+	164 ms	0.62 ms	0.79 ms	263x	1.2x faster
Char class [\w]+	478 ms	42.1 ms	56.4 ms	11x	1.3x faster
Word repeat (\w{2,8})+	690 ms	180 ms	54.7 ms	3x	3.2x slower

Where coregex excels:

• Multiline patterns ((?m)^/.*\.php) — 2.2x faster than Rust, 299x vs stdlib
• IP/phone patterns (\d+\.\d+\.\d+\.\d+) — SIMD digit prefilter skips non-digit regions
• Suffix patterns (.*\.log, .*\.txt) — reverse search optimization (1000x+)
• Inner literals (.*error.*, .*@example\.com) — bidirectional DFA (900x+)
• Multi-pattern (foo|bar|baz|...) — Slim Teddy (≤32), Fat Teddy (33-64), or Aho-Corasick (>64)
• Anchored alternations (^(\d+|UUID|hex32)) — O(1) branch dispatch (5-20x)
• Concatenated char classes ([a-zA-Z]+[0-9]+) — DFA with byte classes (5-7x)
• Zero-alloc iterators (AllIndex, AppendAllIndex) — 0 heap allocs, up to 30% faster than FindAll. Email pattern faster than Rust with AppendAllIndex.

Features

Engine Selection

coregex automatically selects the optimal engine:

Strategy	Pattern Type	Speedup
AnchoredLiteral	^prefix.*suffix$	32-133x
MultilineReverseSuffix	(?m)^/.*\.php	100-552x ⚡
ReverseInner	.*keyword.*	100-900x
ReverseSuffix	.*\.txt	100-1100x
BranchDispatch	^(\d+|UUID|hex32)	5-20x
CompositeSequenceDFA	[a-zA-Z]+[0-9]+	5-7x
LazyDFA	IP, complex patterns	10-150x
AhoCorasick	a|b|c|...|z (>64 patterns)	75-113x
CharClassSearcher	[\w]+, \d+	4-25x
Slim Teddy	foo|bar|baz (2-32 patterns)	15-240x
Fat Teddy	33-64 patterns	60-73x
OnePass	Anchored captures	10x
BoundedBacktracker	Small patterns	2-5x

API Compatibility

Drop-in replacement for regexp.Regexp:

// stdlib
re := regexp.MustCompile(pattern)

// coregex — same API
re := coregex.MustCompile(pattern)

Supported methods:

• Match, MatchString, MatchReader
• Find, FindString, FindAll, FindAllString
• FindIndex, FindStringIndex, FindAllIndex
• FindSubmatch, FindStringSubmatch, FindAllSubmatch
• ReplaceAll, ReplaceAllString, ReplaceAllFunc
• Split, SubexpNames, NumSubexp
• Longest, Copy, String

Zero-Allocation APIs

// Zero allocations — boolean match
matched := re.IsMatch(text)

// Zero allocations — single match indices
start, end, found := re.FindIndices(text)

// Zero allocations — iterator over all matches (Go 1.23+)
for m := range re.AllIndex(data) {
    fmt.Printf("match at [%d, %d]\n", m[0], m[1])
}

// Zero allocations — match content iterator
for s := range re.AllString(text) {
    fmt.Println(s)
}

// Buffer-reuse — append to caller's slice (strconv.Append* pattern)
var buf [][2]int
for _, chunk := range chunks {
    buf = re.AppendAllIndex(buf[:0], chunk, -1)
    process(buf)
}

Configuration

config := coregex.DefaultConfig()
config.DFAMaxStates = 10000      // Limit DFA cache
config.EnablePrefilter = true    // SIMD acceleration

re, err := coregex.CompileWithConfig(pattern, config)

Thread Safety

A compiled *Regexp is safe for concurrent use by multiple goroutines:

re := coregex.MustCompile(`\d+`)

// Safe: multiple goroutines sharing one compiled pattern
var wg sync.WaitGroup
for i := 0; i < 100; i++ {
    wg.Add(1)
    go func() {
        defer wg.Done()
        re.FindString("test 123 data")  // thread-safe
    }()
}
wg.Wait()

Internally uses sync.Pool (same pattern as Go stdlib regexp) for per-search state management.

Syntax Support

Uses Go's regexp/syntax parser:

Feature	Support
Character classes	[a-z], \d, \w, \s
Quantifiers	*, +, ?, {n,m}
Anchors	^, $, \b, \B
Groups	(...), (?:...), (?P<name>...)
Unicode	\p{L}, \P{N}
Flags	(?i), (?m), (?s)
Backreferences	Not supported (O(n) guarantee)

Architecture

Pattern → Parse → NFA → Literal Extract → Strategy Select
                                               ↓
                  ┌────────────────────────────────────────────┐
                  │ Engines (17 strategies):                   │
                  │  LazyDFA, PikeVM, OnePass,                 │
                  │  BoundedBacktracker, ReverseAnchored,      │
                  │  ReverseInner, ReverseSuffix,              │
                  │  ReverseSuffixSet, MultilineReverseSuffix, │
                  │  AnchoredLiteral, CharClassSearcher,       │
                  │  Teddy, DigitPrefilter, AhoCorasick,       │
                  │  CompositeSearcher, BranchDispatch, Both   │
                  └────────────────────────────────────────────┘
                                               ↓
Input → Prefilter (SIMD) → Engine → Match Result

For detailed architecture documentation, see docs/ARCHITECTURE.md. For optimization details, see docs/OPTIMIZATIONS.md.

SIMD Primitives (AMD64):

• memchr — single byte search (AVX2)
• memmem — substring search (SSSE3)
• Slim Teddy — multi-pattern search, 2-32 patterns (SSSE3, 9+ GB/s)
• Fat Teddy — multi-pattern search, 33-64 patterns (AVX2, 9+ GB/s)

Pure Go fallback on other architectures.

Battle-Tested

coregex was tested in GoAWK. This real-world testing uncovered 15+ edge cases that synthetic benchmarks missed.

Powered by coregex: uawk

uawk is a modern AWK interpreter built on coregex:

Benchmark (10MB)	GoAWK	uawk	Speedup
Regex alternation	1.85s	97ms	19x
IP matching	290ms	99ms	2.9x
General regex	320ms	100ms	3.2x

go install github.com/kolkov/uawk/cmd/uawk@latest
uawk '/error/ { print $0 }' server.log

We need more testers! If you have a project using regexp, try coregex and report issues.

Documentation

• API Reference
• CHANGELOG
• Contributing
• Security Policy

Comparison

	coregex	stdlib	regexp2
Performance	3-3000x faster	Baseline	Slower
SIMD	AVX2/SSSE3	No	No
O(n) guarantee	Yes	Yes	No
Backreferences	No	No	Yes
API	Drop-in	—	Different

Use coregex for performance-critical code with O(n) guarantee. Use stdlib for simple cases where performance doesn't matter. Use regexp2 if you need backreferences (accept exponential worst-case).

Related

• uawk — Ultra AWK interpreter powered by coregex
• kolkov/regex-bench — Cross-language benchmarks
• golang/go#26623 — Go regexp performance discussion
• golang/go#76818 — Upstream path proposal

Inspired by:

• Rust regex — Architecture
• RE2 — O(n) guarantees
• Hyperscan — SIMD algorithms

License

MIT — see LICENSE.

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Status: Pre-1.0 (API may change). Ready for testing and feedback.

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