# WebGPU Bitonic Sort (Unsigned Integers)

This project implements a **GPU-accelerated bitonic sort** for unsigned integers using **WebGPU compute shaders**. It performs a local per-workgroup sort followed by a multi-pass global bitonic merge and measures execution time in the browser.

## Overview

* Sorting algorithm: **Bitonic sort**
* Execution model: **WebGPU compute pipelines**
* Data type: `Uint32`
* Element count: `131,072`
* Workgroup size: `256`
* Execution environment: **Modern browser with WebGPU enabled**

The implementation splits sorting into two stages:

1. **Local sort**
   Each workgroup sorts its local block of data.

2. **Global bitonic merge**
   Multiple compute passes perform the bitonic merge across all workgroups using precomputed `j` and `k` pass parameters.

## Structure

* `WebGpu.js`
  Abstraction layer for creating pipelines, bind groups, and buffers.

* `Measure.js`
  Simple performance measurement utility with optional DOM output.

* `shaders/localSort.wgsl`
  Compute shader for local (per-workgroup) sorting.

* `shaders/bitonicSortUIntMultiPass.wgsl`
  Compute shader for multi-pass global bitonic merging.

## How It Works

1. Request a WebGPU adapter and device.
2. Initialize index buffers and bitonic pass parameters (`jArray`, `kArray`).
3. Run a local compute pass to partially sort data.
4. Run a global bitonic merge with repeated dispatches.
5. Measure execution time for multiple iterations.
6. Read back the result buffer and verify correctness.

After completion, the result is validated on the CPU to ensure that all values are sorted correctly.

## Requirements

* A browser with **WebGPU support** enabled
  (for example Chromium-based browsers with the appropriate flags).
* A GPU and driver that support WebGPU compute shaders.
* A static file server (due to module imports and shader loading).

## Running

Serve the project directory via a local web server and open the page that loads this script.

Example:

```
python3 -m http.server
```

Then open:

```
http://localhost:8000
```

## Output

* Timing results are written to the page via `Measure`.
* Final verification logs to the console:

```
There is error? false 131072
```

If `true`, the GPU sort produced incorrect results.

## Purpose

This project serves as:

* A WebGPU compute benchmark
* A reference implementation of GPU-based bitonic sorting
* A foundation for GPU-accelerated data processing pipelines

## License

MIT