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@stackline/adler-32

Pure-JS ADLER-32.

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Current package version: 1.0.2

Why this package?

Maintained fork of adler-32 1.3.1. Apache-2.0; original copyright notices are retained.

The str function encodes unpaired UTF-16 surrogates as U+FFFD, matching standard UTF-8 encoders. Valid strings, byte inputs, signed results, and seed behavior are preserved.

Requires Node.js 20.19 or newer. No runtime dependencies.

Signed ADLER-32 algorithm implementation in JS (for the browser and nodejs). Emphasis on correctness, performance, and IE6+ support.

Compatibility

Item Value
Package @stackline/adler-32@1.0.2
Supported Node.js >=20.19.0
Module entry adler32.js (CommonJS)
Runtime dependencies 0 direct dependencies
Types types/index.d.ts

Installation

npm install @stackline/adler-32

With npm:

$ npm install @stackline/adler-32

In the browser:

<script src="adler32.js"></script>

The browser exposes a variable ADLER32.

The scoped package does not install an adler32 command. The separate upstream adler32-cli examples below describe that independently installed tool.

The script will manipulate module.exports if available . This is not always desirable. To prevent the behavior, define DO_NOT_EXPORT_ADLER.

Usage

const ADLER32 = require('@stackline/adler-32');
console.log(ADLER32.str('SheetJS')); // 176947863

In all cases, the relevant function takes an argument representing data and an optional second argument representing the starting "seed" (for running hash).

The return value is a signed 32-bit integer.

For example:

// var ADLER32 = require('@stackline/adler-32');           // uncomment if in node
ADLER32.str("SheetJS")                          // 176947863
ADLER32.bstr("SheetJS")                         // 176947863
ADLER32.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // 176947863

adler32 = ADLER32.buf([83, 104])                // 17825980  "Sh"
adler32 = ADLER32.str("eet", adler32)           // 95486458  "Sheet"
ADLER32.bstr("JS", adler32)                     // 176947863  "SheetJS"

[ADLER32.str("\u2603"),  ADLER32.str("\u0003")]  // [ 73138686, 262148 ]
[ADLER32.bstr("\u2603"), ADLER32.bstr("\u0003")] // [ 262148,   262148 ]
[ADLER32.buf([0x2603]),  ADLER32.buf([0x0003])]  // [ 262148,   262148 ]

Features

Performance

make perf will run algorithmic performance tests (which should justify certain decisions in the code).

Bit twiddling is much faster than taking the mod in Safari and Firefox browsers. Instead of taking the literal mod 65521, it is faster to keep it in the integers by bit-shifting: 65536 ~ 15 mod 65521 so for nonnegative integer a:

    a = (a >>> 16) * 65536 + (a & 65535)            [equality]
    a ~ (a >>> 16) * 15    + (a & 65535) mod 65521

The mod is taken at the very end, since the intermediate result may exceed 65521

Magic Number

The magic numbers were chosen so as to not overflow a 31-bit integer:

F[n_] := Reduce[x*(x + 1)*n/2 + (x + 1)*(65521) < (2^31 - 1) && x > 0, x, Integers]
F[255] (* bstr:  x \[Element] Integers && 1 <= x <= 3854 *)
F[127] (* ascii: x \[Element] Integers && 1 <= x <= 5321 *)

Subtract up to 4 elements for the Unicode case.

Security

ADLER-32 detects accidental data changes; it is not a cryptographic hash or an authentication mechanism.

API Surface

The usage reference above documents the existing public API and its input/output behavior.

Local Development

Clone the repository and run the following commands from its root:

npm ci
npm run build
npm test
npm run lint
npm run test:types

The retained upstream development notes below include historical tooling; the commands above are the maintained package checks.

Stackline development

Run npm ci, npm run build, npm test and npm run lint and npm run test:types. The checked-in upstream fixtures and focused regression suite run without downloading external test data.

Upstream testing

make test will run the nodejs-based test.

To run the in-browser tests, run a local server and go to the ctest directory. make ctestserv will start a python SimpleHTTPServer server on port 8000.

To update the browser artifacts, run make ctest.

To generate the bits file, use the adler32 function from python zlib:

>>> from zlib import adler32
>>> x="foo bar baz٪☃🍣"
>>> adler32(x)
1543572022
>>> adler32(x+x)
-2076896149
>>> adler32(x+x+x)
2023497376

The adler32-cli package includes scripts for processing files or text on standard input:

$ echo "this is a test" > t.txt
$ adler32-cli t.txt
726861088

For comparison, the adler32.py script in the subdirectory uses python zlib:

$ packages/adler32-cli/bin/adler32.py t.txt
726861088

Release Checklist

  1. Update the package version, lockfile, generated version fields, and changelog together.
  2. Run the development checks above and audit both npm audit and npm audit --omit=dev.
  3. Use the GitHub publish workflow with its Prod environment to publish the exact CI tarball.
  4. Verify public npm bytes, package identity, provenance, and the immutable GitHub release evidence.

License

Apache-2.0. Original copyright notices and upstream attribution are retained.

Please consult the attached LICENSE file for details. All rights not explicitly granted by the Apache 2.0 license are reserved by the Original Author.

See NOTICE for retained attribution.

Credits and original authors

Original copyright, license notices and contributor acknowledgements remain part of this distribution. Stackline maintenance does not replace authorship of the original work.

Community and Links

Use this repository's issue tracker for reproducible bugs and feature requests. Join r/Stackline for examples, usage questions and release discussions.