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Matt Ryan
Matt Ryan

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Day 31: Radix Sort

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function radixSortUint32(input) {
  const arrayConstr = input.length < (1 << 16) ?
    Uint16Array :
    Uint32Array;
  const numberOfBins = 256 * 4;
  let count = new arrayConstr(numberOfBins);

  let output = new Uint32Array(input.length);

  // count all bytes in one pass
  for (let i = 0; i < input.length; i++) {
    let val = input[i];
    count[val & 0xFF]++;
    count[((val >> 8) & 0xFF) + 256]++;
    count[((val >> 16) & 0xFF) + 512]++;
    count[((val >> 24) & 0xFF) + 768]++;
  }

  // create summed array
  for (let j = 0; j < 4; j++) {
    let t = 0,
      sum = 0,
      offset = j * 256;
    for (let i = 0; i < 256; i++) {
      t = count[i + offset];
      count[i + offset] = sum;
      sum += t;
    }
  }

  for (let i = 0; i < input.length; i++) {
    let val = input[i];
    output[count[val & 0xFF]++] = val;
  }
  for (let i = 0; i < input.length; i++) {
    let val = output[i];
    input[count[((val >> 8) & 0xFF) + 256]++] = val;
  }
  for (let i = 0; i < input.length; i++) {
    let val = input[i];
    output[count[((val >> 16) & 0xFF) + 512]++] = val;
  }
  for (let i = 0; i < input.length; i++) {
    let val = output[i];
    input[count[((val >> 24) & 0xFF) + 768]++] = val;
  }

  return input;
}
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This post blew up on DEV in 2020:

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🚀⚙️ JavaScript Visualized: the JavaScript Engine

As JavaScript devs, we usually don't have to deal with compilers ourselves. However, it's definitely good to know the basics of the JavaScript engine and see how it handles our human-friendly JS code, and turns it into something machines understand! 🥳

Happy coding!

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