bun.sh/bench/snippets/concat.js

import { allocUnsafe } from "bun";
import { readFileSync } from "fs";
import { bench, group, run } from "../runner.mjs";

function polyfill(chunks) {
  var size = 0;
  for (const chunk of chunks) {
    size += chunk.byteLength;
  }
  var buffer = new ArrayBuffer(size);
  var view = new Uint8Array(buffer);
  var offset = 0;
  for (const chunk of chunks) {
    view.set(chunk, offset);
    offset += chunk.byteLength;
  }
  return buffer;
}

function polyfillUninitialized(chunks) {
  var size = 0;
  for (const chunk of chunks) {
    size += chunk.byteLength;
  }
  var view = allocUnsafe(size);

  var offset = 0;
  for (const chunk of chunks) {
    view.set(chunk, offset);
    offset += chunk.byteLength;
  }
  return view.buffer;
}

const chunkGroups = [
  [Uint8Array.from([123]), Uint8Array.from([456]), Uint8Array.from([789])],
  Array.from(readFileSync(import.meta.path)).map(a => Uint8Array.from([a])),
  [readFileSync(import.meta.path)],
  Array.from({ length: 42 }, () => readFileSync(import.meta.path)),
  Array.from({ length: 2 }, () => new TextEncoder().encode(readFileSync(import.meta.path, "utf8").repeat(100))),
];

for (const chunks of chunkGroups) {
  const name = `${chunks.reduce((prev, curr, i, a) => prev + curr.byteLength, 0)} bytes for ${chunks.length} chunks`
  group(name, () => {
    bench(`Bun.concatArrayBuffers (${name})`, () => {
      Bun.concatArrayBuffers(chunks);
    });
    bench(`Uint8Array.set (${name})`, () => {
      polyfill(chunks);
    });

    bench(`Uint8Array.set (uninitialized memory) (${name})`, () => {
      polyfillUninitialized(chunks);
    });
  });
}

await run();