ts-adler32

A direct TypeScript port of an Adler-32 reference implementation (RFC 1950).

If you find this project useful, you can support this and further ports at ko-fi.com/scottmoore0.

Upstream provenance

This package is a TypeScript port of shixiongfei/adler32 (adler32.c, adler32.h) by Xiongfei Shi, Apache License 2.0.

The translated output is validated against canonical Adler-32 reference values from RFC 1950 §9 plus the Wikipedia reference ("Wikipedia" → 0x11E60398).

Why this exists

Adler-32 is the integrity checksum used by zlib / deflate / PNG at the protocol level. Wherever a zlib stream appears (gzip, HTTP Content-Encoding: deflate, PNG IDAT, Git pack objects, ZIP entries with deflate), there's an Adler-32 at the end of the compressed stream. It is slightly faster than CRC-32 to compute in software (no table) and has a known weakness on very short inputs (use CRC-32 for short messages where every bit matters).

ts-adler32 is a direct mechanical translation from a small reference via the cpp-to-ts translator, so its relationship to the algorithm is inspectable.

Install

npm install ts-adler32

Usage

import { adler32sum, adler32hex, adler32combine } from 'ts-adler32';

// Numeric
adler32sum('abc');                  // 38600999 (= 0x024D0127)

// Hex
adler32hex('abc');                  // '024d0127'

// Custom seed (continue from a previous Adler-32)
const a = adler32sum('Hello, ');
const b = adler32sum('World!', a);  // = adler32sum('Hello, World!')

// Combine two checksums of concatenated streams (zlib trick)
const fullByCombine = adler32combine(a, adler32sum('World!'), 'World!'.length);

API surface

• adler32sum(input: Uint8Array | string, seed?: number): number — Adler-32, returns uint32. seed defaults to 1 per RFC 1950.
• adler32hex(input, seed?): string — 8-character lowercase hex.
• adler32combine(adlerA: number, adlerB: number, lenB: number): number — combine two checksums of concatenated buffers.
• adler32roll(currentAdler, inByte, outByte, windowSize): number — sliding-window rolling update.
• ADLER32_INIT = 1 — exported constant.

Reference values

The test suite asserts against these canonical Adler-32 values (matching zlib's adler32()):

| Input | Adler-32 | |---|---| | "" | 00000001 | | "a" | 00620062 | | "abc" | 024d0127 | | "message digest" | 29750586 | | "abcdefghijklmnopqrstuvwxyz" | 90860b20 | | "The quick brown fox jumps over the lazy dog" | 5bdc0fda | | "Wikipedia" (Wikipedia article example) | 11e60398 |

Run:

npm test

Caveats

• Not cryptographic. Adler-32 is easily forged. Use SHA-256 (ts-sha2) when adversaries matter.
• Weak on short inputs. For inputs shorter than a few hundred bytes, prefer CRC-32 (ts-crc32) — Adler-32's error-detection guarantees are reduced for very short strings.
• Used by zlib/PNG/Git. If you're decoding/encoding a zlib stream, the trailer Adler-32 must match the original-data Adler-32 (not the compressed-data Adler-32).

License

Apache 2.0. Original C by Xiongfei Shi under Apache 2.0.

See also

• ts-crc32 — CRC-32 (IEEE 802.3), stronger for short inputs
• ts-xxhash — much faster non-cryptographic hash
• ts-sha2 — SHA-256 for cryptographic integrity
• cpp-to-ts — the translator that produced this package