comtains

comtains expands static byte sequences into zero-allocation matchers at compile time. The byte_set! macro emits a branch-ordered decision tree, keeping membership checks to a handful of predictable instructions—ideal for tight opcode dispatchers or protocol parsers.

use comtains::{byte_set, ByteSet};

const HTTP_METHODS: ByteSet = byte_set![b"GET", b"POST", b"PUT", b"PATCH"];

assert!(HTTP_METHODS.contains(b"GET"));
assert!(!HTTP_METHODS.contains(b"DELETE"));

How it works

1. All inputs are parsed at macro expansion time into a trie that shares common prefixes.
2. Each edge records how many sequences traverse it; siblings are sorted by descending weight to probe common paths first.
3. The macro generates a nested match ladder that compares candidate[depth], short-circuiting on the first mismatch.
4. Debug metadata is emitted alongside the matcher so tests and benchmarks can assert branch ordering or inspect the trie layout.

Motivation

This crate originated from a research project involving QEMU introspection for dynamic malware analysis.
Part of the system hooks Translation Blocks (TCGs) during translation and needs to efficiently decide whether a given translated basic block ends with specific opcodes—such as syscall instructions.
To keep this decision fast and early in the translation process, a zero-allocation, compile-time matcher for static byte patterns was required.
comtains was built to fulfill this exact need: performing rapid membership checks on fixed opcode sets with minimal branching and no runtime overhead.