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

Withnpm:

$ npm install adler-32

In the browser:

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

The browser exposes a variableADLER32.

When installed globally, npm installs a scriptadler32 that computes thechecksum for a specified file or standard input.

The script will manipulatemodule.exports if available . This is not alwaysdesirable. To prevent the behavior, defineDO_NOT_EXPORT_ADLER.

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

The return value is a signed 32-bit integer.

• ADLER32.buf(byte array or buffer[, seed]) assumes the argument is a sequenceof 8-bit unsigned integers (nodejsBuffer,Uint8Array or array of bytes).

• ADLER32.bstr(binary string[, seed]) assumes the argument is a binary stringwhere bytei is the low byte of the UCS-2 char:str.charCodeAt(i) & 0xFF

• ADLER32.str(string) assumes the argument is a standard JS string andcalculates the hash of the UTF-8 encoding.

For example:

// var ADLER32 = require('adler-32');           // uncomment if in nodeADLER32.str("SheetJS")// 176947863ADLER32.bstr("SheetJS")// 176947863ADLER32.buf([83,104,101,101,116,74,83])// 176947863adler32=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 ]

make test will run the nodejs-based test.

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

To update the browser artifacts, runmake ctest.

To generate the bits file, use theadler32 function from pythonzlib:

>>>fromzlibimportadler32>>>x="foo bar baz٪☃🍣">>>adler32(x)1543572022>>>adler32(x+x)-2076896149>>>adler32(x+x+x)2023497376

Theadler32-cli package includesscripts for processing files or text on standard input:

$echo"this is a test"> t.txt$ adler32-cli t.txt726861088

For comparison, theadler32.py script in the subdirectory uses pythonzlib:

$ packages/adler32-cli/bin/adler32.py t.txt726861088

make perf will run algorithmic performance tests (which should justify certaindecisions 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 integersby bit-shifting:65536 ~ 15 mod 65521 so for nonnegative integera:

    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

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.

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