Benchmark: Math.sqrt() vs Fast inverse sqrt

Script Preparation code:

let v = 123.75;

function test1() {
  let r;
  for(let i = 0; i < 2000; ++i)
    r = 1 / Math.sqrt(v);
}

function test2() {
  let r;
  for(let i = 0; i < 2000; ++i)
    r = Q_sqrt(v);
}

function Q_sqrt(num) {
  let i = [];
  let y = [];
  
  y[0] = num;
  i[0] = 0x5f375a86 - (i[0] >> 1);
  
  y[0] = y[0] * (1.5 * ((num * 0.5) * y[0] * y[0]));
  
  return y[0];
}

Tests:

1 / Math.sqrt()
test1();
Fast inverse sqrt
test2();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
1 / Math.sqrt()
Fast inverse sqrt

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 months ago)

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 132 on Android

View result in a separate tab

Test name	Executions per second
1 / Math.sqrt()	919036.6 Ops/sec
Fast inverse sqrt	5572.2 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

Let's break down the provided JSON benchmark definition and explain what is being tested, compared, and considered.

**Benchmark Definition**

The benchmark tests two different ways to calculate the inverse square root of a number:

1. `Math.sqrt()`: The built-in JavaScript function `Math.sqrt()` is used to calculate the square root of a number.
2. "Fast inverse sqrt" ( alias: Q_sqrt ): A custom implementation of the inverse square root calculation, which uses a specific algorithm to avoid division.

**Options compared**

The two options are compared in terms of their execution time and performance on different devices.

**Pros and Cons**

1. **Math.sqrt()**
	* Pros:
		+ Widely supported and well-maintained.
		+ Easy to implement and understand.
	* Cons:
		+ May be slower than the custom implementation for large numbers or specific use cases.
2. "Fast inverse sqrt" (Q_sqrt)
	* Pros:
		+ Optimized for performance, potentially faster than Math.sqrt() for certain use cases.
		+ Can be used in situations where a more accurate inverse square root is required.
	* Cons:
		+ Custom implementation requires manual optimization and may not be as widely supported.
		+ Requires understanding of the custom algorithm and its potential pitfalls.

**Library**

The Q_sqrt function uses a library-like implementation, which appears to be a self-contained, optimized algorithm for calculating the inverse square root. The library is not explicitly named in the JSON, but it's likely that this is a proprietary or open-source implementation developed specifically for performance-critical applications.

**Special JS feature or syntax**

There are no special JavaScript features or syntax used in this benchmark. However, the Q_sqrt function relies on bitwise operations and exponentiation, which may be optimized by modern JavaScript engines to some extent.

**Alternative approaches**

Other alternative approaches to calculating the inverse square root could include:

1. Using a different mathematical library or framework that provides an optimized implementation.
2. Implementing a hybrid approach that combines the built-in Math.sqrt() function with custom optimization for specific use cases.
3. Utilizing GPU acceleration or other parallel processing techniques to improve performance.

**Other considerations**

When choosing between these two options, consider the following factors:

1. Performance requirements: If high-performance is critical, the Q_sqrt implementation might be a better choice.
2. Code maintainability and readability: The built-in Math.sqrt() function is generally easier to understand and maintain.
3. Compatibility and support: Ensure that both options are supported by your target platforms and browsers.

Overall, this benchmark provides a useful comparison of two approaches to calculating the inverse square root in JavaScript, highlighting the trade-offs between built-in functions and custom optimizations.

Related benchmarks:

Math.sqrt() vs Fast inverse sqrt (version: 0)

Comparing performance of: 1 / Math.sqrt() vs Fast inverse sqrt

Created: 4 years ago by: Guest

Jump to the latest result

1 / Math.sqrt()

Fast inverse sqrt

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):