17
CRC-32 Checksum in WASM and Raw JS: Tutorial and Benchmark
In this tutorial we'll build a cyclic redundancy check (CRC) hashing function. More specifically, its 32 bit variant called "CRC-32". I bumped into it in the PNG specification, but it's also used in Gzip and bunch of other formats and protocols. In short, it makes a tiny (4 bytes) hash out of whatever binary data you feed to it and changes significantly if data changes even slightly. Of course, such a tiny function is not even close to be crypto secure, therefore it's only used to check if data was transferred correctly.
I love JavaScript, but writing binary algorithm implementations in it is a torture thanks to signed integers conversion in bitwise operations. So, I've decided to write implementation in a strongly typed system language, my other favourite, rust and compile it to WebAssembly.
WebAssembly (a.k.a. WASM) provides a virtual machine that can be created from JavaScript environment (browser, nodejs or deno). This machine is super limited and runs only one binary program in a sandbox environment. It might sound boring, but, in fact, it can run almost anything: media manipulation software, AI, games - you name it.
If you are on a MacOS/Linux/other Unix machine installing rust is as simple as running this command in a terminal and following interactive instructions:
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | shTo install on other OS refer to rustup installation instructions
Once you're done this should work:
rustc --version
# rustc 1.53.0 (53cb7b09b 2021-06-17)Next step is to install wasm-pack, a tool that compiles your WebAssembly module, generates JavaScript glue and TypeScript types for it.
If you're on a Unix machine the command is:
curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | shFor other OS: refer to wasm-pack installation instructions.
Once again, make sure it's working:
wasm-pack --version
# wasm-pack 0.10.0Rust comes with its own dependency manager cargo. It also helps with some routine operations, like project creation. Run this command to generate project folder and navigate into it:
cargo new --lib wasm-test && cd wasm-testWe should add crate type (cdylib) and the wasm binding dependency (wasm-bindgen) in the generated Cargo.toml:
[package]
name = "wasm-test"
version = "0.1.0"
edition = "2018"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[lib]
crate-type = ["cdylib"]
[dependencies]
wasm-bindgen = "0.2"Now let's add the CRC-32 algorithm implementation to src/lib.rs:
use wasm_bindgen::prelude::*;
// Pre-computed, see tests
const CRC_TABLE: [u32; 256] = [
0, 1996959894, 3993919788, 2567524794, 124634137, 1886057615, 3915621685, 2657392035,
249268274, 2044508324, 3772115230, 2547177864, 162941995, 2125561021, 3887607047, 2428444049,
498536548, 1789927666, 4089016648, 2227061214, 450548861, 1843258603, 4107580753, 2211677639,
325883990, 1684777152, 4251122042, 2321926636, 335633487, 1661365465, 4195302755, 2366115317,
997073096, 1281953886, 3579855332, 2724688242, 1006888145, 1258607687, 3524101629, 2768942443,
901097722, 1119000684, 3686517206, 2898065728, 853044451, 1172266101, 3705015759, 2882616665,
651767980, 1373503546, 3369554304, 3218104598, 565507253, 1454621731, 3485111705, 3099436303,
671266974, 1594198024, 3322730930, 2970347812, 795835527, 1483230225, 3244367275, 3060149565,
1994146192, 31158534, 2563907772, 4023717930, 1907459465, 112637215, 2680153253, 3904427059,
2013776290, 251722036, 2517215374, 3775830040, 2137656763, 141376813, 2439277719, 3865271297,
1802195444, 476864866, 2238001368, 4066508878, 1812370925, 453092731, 2181625025, 4111451223,
1706088902, 314042704, 2344532202, 4240017532, 1658658271, 366619977, 2362670323, 4224994405,
1303535960, 984961486, 2747007092, 3569037538, 1256170817, 1037604311, 2765210733, 3554079995,
1131014506, 879679996, 2909243462, 3663771856, 1141124467, 855842277, 2852801631, 3708648649,
1342533948, 654459306, 3188396048, 3373015174, 1466479909, 544179635, 3110523913, 3462522015,
1591671054, 702138776, 2966460450, 3352799412, 1504918807, 783551873, 3082640443, 3233442989,
3988292384, 2596254646, 62317068, 1957810842, 3939845945, 2647816111, 81470997, 1943803523,
3814918930, 2489596804, 225274430, 2053790376, 3826175755, 2466906013, 167816743, 2097651377,
4027552580, 2265490386, 503444072, 1762050814, 4150417245, 2154129355, 426522225, 1852507879,
4275313526, 2312317920, 282753626, 1742555852, 4189708143, 2394877945, 397917763, 1622183637,
3604390888, 2714866558, 953729732, 1340076626, 3518719985, 2797360999, 1068828381, 1219638859,
3624741850, 2936675148, 906185462, 1090812512, 3747672003, 2825379669, 829329135, 1181335161,
3412177804, 3160834842, 628085408, 1382605366, 3423369109, 3138078467, 570562233, 1426400815,
3317316542, 2998733608, 733239954, 1555261956, 3268935591, 3050360625, 752459403, 1541320221,
2607071920, 3965973030, 1969922972, 40735498, 2617837225, 3943577151, 1913087877, 83908371,
2512341634, 3803740692, 2075208622, 213261112, 2463272603, 3855990285, 2094854071, 198958881,
2262029012, 4057260610, 1759359992, 534414190, 2176718541, 4139329115, 1873836001, 414664567,
2282248934, 4279200368, 1711684554, 285281116, 2405801727, 4167216745, 1634467795, 376229701,
2685067896, 3608007406, 1308918612, 956543938, 2808555105, 3495958263, 1231636301, 1047427035,
2932959818, 3654703836, 1088359270, 936918000, 2847714899, 3736837829, 1202900863, 817233897,
3183342108, 3401237130, 1404277552, 615818150, 3134207493, 3453421203, 1423857449, 601450431,
3009837614, 3294710456, 1567103746, 711928724, 3020668471, 3272380065, 1510334235, 755167117,
];
/**
* Reference implementation
* http://libpng.org/pub/png/spec/iso/index-object.html#D-CRCAppendix
*/
#[wasm_bindgen]
pub fn crc(buf: Vec<u8>) -> u32 {
let mut c: u32 = 0xffffffff;
for v in buf {
let idx: usize = (c as usize ^ v as usize) & 0xff;
c = CRC_TABLE[idx] ^ (c >> 8);
}
c ^ 0xffffffff
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_table() {
let mut crc_table: [u32; 256] = [0; 256];
let mut c: usize;
for n in 0..256 {
c = n;
for _ in 0..8 {
c = if c & 1 == 1 {
0xedb88320 ^ (c >> 1)
} else {
c >> 1
}
}
crc_table[n] = c as u32;
}
assert_eq!(CRC_TABLE, crc_table);
}
#[test]
fn test_iend() {
assert_eq!(crc("IEND".as_bytes().to_vec()), 0xAE426082);
}
}The implementation uses pre-computed table for each byte value from 0x00 to 0xff and boils down to couple bitwise operations.
Macros #[wasm_bindgen] marks the function we want to export.
The unit tests in the end of the file can be run with:
cargo test
# running 2 tests
# test tests::test_iend ... ok
# test tests::test_table ... ok
# test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00sRun this command:
wasm-pack build --target web --releaseIt creates a pkg folder with WASM module, TypeScript types, package.json and the main wasm_test.js file.
Let's create index.html file in the project root and import the generated script from there:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>WASM Test</title>
</head>
<body>
<div>
<textarea id="input" placeholder="Place your data here">
Hello,WASM!</textarea
>
<br />
<textarea
id="output"
readonly
placeholder="Resulting HEX will be displayed here"
></textarea>
<br />
<button disabled id="btn">Calculate CRC-32</button>
</div>
<script type="module">
import init, { crc } from "./pkg/wasm_test.js";
const btn = document.getElementById("btn");
const input = document.getElementById("input");
const output = document.getElementById("output");
init().then(() => {
btn.disabled = false;
btn.onclick = () => {
const buffer = new TextEncoder().encode(input.value);
output.value = crc(buffer).toString(16);
};
});
</script>
</body>
</html>For security reasons you won't be able to test this html file by simply opening it, but you can start a simple file server with:
npx serve .
# npx: installed 88 in 6.469s
#
# ┌────────────────────────────────────────┐
# │ │
# │ Serving! │
# │ │
# │ Local: http://localhost:5000 │
# │ │
# │ Copied local address to clipboard! │
# │ │
# └────────────────────────────────────────┘
#If you can't run this command, that probably means that either NodeJS or NPM is not installed.
Navigate your browser to http://localhost:5000 and click the "Calculate CRC-32" button to see something like this:
Let's create nearly identical JavaScript implementation of CRC-32 in crc.js:
const CRC_TABLE = new Uint32Array([
0, 1996959894, 3993919788, 2567524794, 124634137, 1886057615, 3915621685,
2657392035, 249268274, 2044508324, 3772115230, 2547177864, 162941995,
2125561021, 3887607047, 2428444049, 498536548, 1789927666, 4089016648,
2227061214, 450548861, 1843258603, 4107580753, 2211677639, 325883990,
1684777152, 4251122042, 2321926636, 335633487, 1661365465, 4195302755,
2366115317, 997073096, 1281953886, 3579855332, 2724688242, 1006888145,
1258607687, 3524101629, 2768942443, 901097722, 1119000684, 3686517206,
2898065728, 853044451, 1172266101, 3705015759, 2882616665, 651767980,
1373503546, 3369554304, 3218104598, 565507253, 1454621731, 3485111705,
3099436303, 671266974, 1594198024, 3322730930, 2970347812, 795835527,
1483230225, 3244367275, 3060149565, 1994146192, 31158534, 2563907772,
4023717930, 1907459465, 112637215, 2680153253, 3904427059, 2013776290,
251722036, 2517215374, 3775830040, 2137656763, 141376813, 2439277719,
3865271297, 1802195444, 476864866, 2238001368, 4066508878, 1812370925,
453092731, 2181625025, 4111451223, 1706088902, 314042704, 2344532202,
4240017532, 1658658271, 366619977, 2362670323, 4224994405, 1303535960,
984961486, 2747007092, 3569037538, 1256170817, 1037604311, 2765210733,
3554079995, 1131014506, 879679996, 2909243462, 3663771856, 1141124467,
855842277, 2852801631, 3708648649, 1342533948, 654459306, 3188396048,
3373015174, 1466479909, 544179635, 3110523913, 3462522015, 1591671054,
702138776, 2966460450, 3352799412, 1504918807, 783551873, 3082640443,
3233442989, 3988292384, 2596254646, 62317068, 1957810842, 3939845945,
2647816111, 81470997, 1943803523, 3814918930, 2489596804, 225274430,
2053790376, 3826175755, 2466906013, 167816743, 2097651377, 4027552580,
2265490386, 503444072, 1762050814, 4150417245, 2154129355, 426522225,
1852507879, 4275313526, 2312317920, 282753626, 1742555852, 4189708143,
2394877945, 397917763, 1622183637, 3604390888, 2714866558, 953729732,
1340076626, 3518719985, 2797360999, 1068828381, 1219638859, 3624741850,
2936675148, 906185462, 1090812512, 3747672003, 2825379669, 829329135,
1181335161, 3412177804, 3160834842, 628085408, 1382605366, 3423369109,
3138078467, 570562233, 1426400815, 3317316542, 2998733608, 733239954,
1555261956, 3268935591, 3050360625, 752459403, 1541320221, 2607071920,
3965973030, 1969922972, 40735498, 2617837225, 3943577151, 1913087877,
83908371, 2512341634, 3803740692, 2075208622, 213261112, 2463272603,
3855990285, 2094854071, 198958881, 2262029012, 4057260610, 1759359992,
534414190, 2176718541, 4139329115, 1873836001, 414664567, 2282248934,
4279200368, 1711684554, 285281116, 2405801727, 4167216745, 1634467795,
376229701, 2685067896, 3608007406, 1308918612, 956543938, 2808555105,
3495958263, 1231636301, 1047427035, 2932959818, 3654703836, 1088359270,
936918000, 2847714899, 3736837829, 1202900863, 817233897, 3183342108,
3401237130, 1404277552, 615818150, 3134207493, 3453421203, 1423857449,
601450431, 3009837614, 3294710456, 1567103746, 711928724, 3020668471,
3272380065, 1510334235, 755167117,
]);
function update_crc(crc, buf) {
let c = crc;
for (const v of buf) {
const idx = ((c ^ v) & 0xff) >>> 0;
c = (CRC_TABLE[idx] ^ (c >>> 8)) >>> 0;
}
return c;
}
export default (buf) => (update_crc(0xffffffff, buf) ^ 0xffffffff) >>> 0;The only thing that differs is the unsigned right shift (>>>) we added to get rid of signs in JS numbers.
We can now include this implementation along with some performance measurements in index.html:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>WASM Test</title>
</head>
<body>
<div>
<textarea id="input" placeholder="Place your data here">
Hello,WASM!</textarea
>
<br />
<textarea
id="output"
readonly
placeholder="Resulting HEX will be displayed here"
></textarea>
<br />
<button disabled id="btn-wasm">Calculate CRC-32 (WASM)</button
><button id="btn-js">Calculate CRC-32 ( JS )</button>
</div>
<script type="module">
import init, { crc } from "./pkg/wasm_test.js";
import crcjs from "./crc.js";
const input = document.getElementById("input");
const output = document.getElementById("output");
const calculate = (fn, name) => {
const buffer = new TextEncoder().encode(input.value);
const t0 = performance.now();
output.value = fn(buffer).toString(16);
const t1 = performance.now();
console.log(`${name}: ${t1 - t0} ms`);
};
document.getElementById("btn-js").onclick = () => calculate(crcjs, "js");
init().then(() => {
const btnWASM = document.getElementById("btn-wasm");
btnWASM.disabled = false;
btnWASM.onclick = () => calculate(crc, "wasm");
});
</script>
</body>
</html>Reload the page and check it out (open console to see performance information):
Not bad, WASM is nearly three times faster on 5 paragraphs of text, but both of them are still very fast. How about a bigger challenge?
Update index.html one last time:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>WASM Test</title>
</head>
<body>
<div>
<textarea id="input" placeholder="Place your data here">
Hello,WASM!</textarea
>
<br />
<textarea
id="output"
readonly
placeholder="Resulting HEX will be displayed here"
></textarea>
<br />
<button disabled id="btn-wasm">Calculate CRC-32 (WASM)</button
><button id="btn-js">Calculate CRC-32 ( JS )</button>
<hr />
<button id="btn-test" disabled>Compare Performance</button>
<div id="result"></div>
</div>
<script type="module">
import init, { crc } from "./pkg/wasm_test.js";
import crcjs from "./crc.js";
const input = document.getElementById("input");
const output = document.getElementById("output");
const calculate = (fn, name) => {
const buffer = new TextEncoder().encode(input.value);
const t0 = performance.now();
output.value = fn(buffer).toString(16);
const t1 = performance.now();
console.log(`${name}: ${t1 - t0} ms`);
};
document.getElementById("btn-js").onclick = () => calculate(crcjs, "js");
init().then(() => {
const btnWASM = document.getElementById("btn-wasm");
btnWASM.disabled = false;
btnWASM.onclick = () => calculate(crc, "wasm");
const btnTest = document.getElementById("btn-test");
btnTest.disabled = false;
const result = document.getElementById("result");
btnTest.onclick = () => {
// Max random buffer
result.innerHTML = "";
const data = window.crypto.getRandomValues(new Uint8Array(65536));
console.info("Test data", data);
const t10 = performance.now();
const hash1 = crcjs(data).toString(16);
const t11 = performance.now();
result.innerHTML += ``;
console.info("JS hash", hash1.toString(16));
const t00 = performance.now();
const hash2 = crc(data).toString(16);
const t01 = performance.now();
result.innerHTML += ``;
console.info("WASM hash", hash2.toString(16));
};
});
</script>
</body>
</html>I've added the third button that creates a big random binary array (65.5Kb), marks time, runs JS and WASM CRC-32 implementation over that buffer and shares the findings.
Here are the results I got in Edge, Safari and Firefox:
Similarly to web target, we can build NodeJS-friendly package by running:
wasm-pack build --target nodejs --out-dir pkg-node --releaseThe contents of pkg-node are mostly the same as web pkg, except for wasm_test.js, that now reads WASM module from the file system.
Create index.js with:
const { PerformanceObserver, performance } = require("perf_hooks");
const crypto = require("crypto");
const { crc } = require("./pkg-node/wasm_test.js");
const crcJS = require("./crc.cjs");
const perfObserver = new PerformanceObserver((items) => {
items.getEntries().forEach((entry) => {
console.log(entry.name, entry.duration, "ms");
});
});
perfObserver.observe({ entryTypes: ["measure"], buffer: true });
const size = 10_000_000;
crypto.randomBytes(size, (err, data) => {
if (err) throw err;
console.log(`Generated random ${(size / 1_000_000).toFixed(0)}MB of data`);
performance.mark("wasm-start");
const crcwasm = crc(data);
performance.mark("wasm-end");
performance.mark("js-start");
const crcjs = crcJS(data);
performance.mark("js-end");
console.assert(crcjs, crcwasm, "CRC values differ!");
performance.measure("js ", "js-start", "js-end");
performance.measure("wasm", "wasm-start", "wasm-end");
});The imported CommonJS script crc.cjs is identical to crc.js apart from the last line ( export default => module.exports):
const CRC_TABLE = new Uint32Array([
0, 1996959894, 3993919788, 2567524794, 124634137, 1886057615, 3915621685,
2657392035, 249268274, 2044508324, 3772115230, 2547177864, 162941995,
2125561021, 3887607047, 2428444049, 498536548, 1789927666, 4089016648,
2227061214, 450548861, 1843258603, 4107580753, 2211677639, 325883990,
1684777152, 4251122042, 2321926636, 335633487, 1661365465, 4195302755,
2366115317, 997073096, 1281953886, 3579855332, 2724688242, 1006888145,
1258607687, 3524101629, 2768942443, 901097722, 1119000684, 3686517206,
2898065728, 853044451, 1172266101, 3705015759, 2882616665, 651767980,
1373503546, 3369554304, 3218104598, 565507253, 1454621731, 3485111705,
3099436303, 671266974, 1594198024, 3322730930, 2970347812, 795835527,
1483230225, 3244367275, 3060149565, 1994146192, 31158534, 2563907772,
4023717930, 1907459465, 112637215, 2680153253, 3904427059, 2013776290,
251722036, 2517215374, 3775830040, 2137656763, 141376813, 2439277719,
3865271297, 1802195444, 476864866, 2238001368, 4066508878, 1812370925,
453092731, 2181625025, 4111451223, 1706088902, 314042704, 2344532202,
4240017532, 1658658271, 366619977, 2362670323, 4224994405, 1303535960,
984961486, 2747007092, 3569037538, 1256170817, 1037604311, 2765210733,
3554079995, 1131014506, 879679996, 2909243462, 3663771856, 1141124467,
855842277, 2852801631, 3708648649, 1342533948, 654459306, 3188396048,
3373015174, 1466479909, 544179635, 3110523913, 3462522015, 1591671054,
702138776, 2966460450, 3352799412, 1504918807, 783551873, 3082640443,
3233442989, 3988292384, 2596254646, 62317068, 1957810842, 3939845945,
2647816111, 81470997, 1943803523, 3814918930, 2489596804, 225274430,
2053790376, 3826175755, 2466906013, 167816743, 2097651377, 4027552580,
2265490386, 503444072, 1762050814, 4150417245, 2154129355, 426522225,
1852507879, 4275313526, 2312317920, 282753626, 1742555852, 4189708143,
2394877945, 397917763, 1622183637, 3604390888, 2714866558, 953729732,
1340076626, 3518719985, 2797360999, 1068828381, 1219638859, 3624741850,
2936675148, 906185462, 1090812512, 3747672003, 2825379669, 829329135,
1181335161, 3412177804, 3160834842, 628085408, 1382605366, 3423369109,
3138078467, 570562233, 1426400815, 3317316542, 2998733608, 733239954,
1555261956, 3268935591, 3050360625, 752459403, 1541320221, 2607071920,
3965973030, 1969922972, 40735498, 2617837225, 3943577151, 1913087877,
83908371, 2512341634, 3803740692, 2075208622, 213261112, 2463272603,
3855990285, 2094854071, 198958881, 2262029012, 4057260610, 1759359992,
534414190, 2176718541, 4139329115, 1873836001, 414664567, 2282248934,
4279200368, 1711684554, 285281116, 2405801727, 4167216745, 1634467795,
376229701, 2685067896, 3608007406, 1308918612, 956543938, 2808555105,
3495958263, 1231636301, 1047427035, 2932959818, 3654703836, 1088359270,
936918000, 2847714899, 3736837829, 1202900863, 817233897, 3183342108,
3401237130, 1404277552, 615818150, 3134207493, 3453421203, 1423857449,
601450431, 3009837614, 3294710456, 1567103746, 711928724, 3020668471,
3272380065, 1510334235, 755167117,
]);
function update_crc(crc, buf) {
let c = crc;
for (const v of buf) {
const idx = ((c ^ v) & 0xff) >>> 0;
c = (CRC_TABLE[idx] ^ (c >>> 8)) >>> 0;
}
return c;
}
module.exports = (buf) => (update_crc(0xffffffff, buf) ^ 0xffffffff) >>> 0;Finally, run the script:
node index
# Generated random 10MB of data
# js 253.875679 ms
# wasm 39.126159 msThe bigger the size of the data to hash, the bigger is the gap between JS and WASM speeds:
# Generated random 100MB of data
js 2461.758713 ms
wasm 389.698142 ms
# Generated random 1000MB of data
js 25945.486315 ms
wasm 3763.860294 msHope you've enjoyed the post! Share your feedback, thoughts and ideas in the comments. Till the next time!
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