Benchmark: Math.round vs Bitwise

Script Preparation code:

var n = Math.PI

Tests:

Math.round(n)
Math.round(n)
Bitwise n + (n < 0 ? -0.5 : 0.5)>>0
n + (n < 0 ? -0.5 : 0.5)>>0

Historical Performance Data aggregated from 8 community runs

Desktop Results:

Chrome 8 runs

Bitwise n + (n < 0 ? -0.5 : 0.5)>>0

65.3M/s

Math.round(n)

52.3M/s

Fastest: Bitwise n + (n < 0 ? -0.5 : 0.5)>>0 (1.2x faster)

View exact numbers

✓ Bitwise n + (n < 0 ? -0.5 : 0.5)>>0: 65,279,460 ops/sec
• Math.round(n): 52,342,120 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Math.round(n)
Bitwise n + (n < 0 ? -0.5 : 0.5)>>0

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 11 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Safari/537.36 Edg/140.0.0.0

Browser/OS: Chrome 140 on Windows

View result in a separate tab

Math.round(n)

274.3M/s

Bitwise n + (n < 0 ? -0.5 : 0.5)>>0

169.6M/s

View exact numbers

Test name	Executions per second
✓ Math.round(n)	274,273,184 Ops/sec
Bitwise n + (n < 0 ? -0.5 : 0.5)>>0	169,586,400 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

I'd be happy to explain the provided benchmark.

**Overview**

The provided benchmark compares two approaches for rounding numbers in JavaScript: `Math.round()` and bitwise operations. The test case checks which approach is faster, with a sample value of `n = Math.PI`.

**Options Compared**

Two options are compared:

1. **`Math.round(n)`**: This method uses the built-in `round()` function from the JavaScript Math object to round `n` to the nearest integer.
2. **`n + (n < 0 ? -0.5 : 0.5)>>0`**: This expression uses a bitwise operation to simulate rounding `n` to the nearest integer. It works by adding `-0.5` to `n` if `n` is negative, and then taking the absolute value of the result using the right-shift operator (`>>`). This effectively rounds down for negative numbers and rounds up for positive numbers.

**Pros and Cons**

* **`Math.round(n)`**: Pros:
	+ Widely supported and well-tested.
	+ Easy to understand and use.
Cons:
	+ May be slower than bitwise operations due to the overhead of calling a function.
* **Bitwise operation**: Pros:
	+ Can be faster than `Math.round()` due to avoiding function calls.
	+ Uses a simple, intuitive expression.
Cons:
	+ Less well-known and less widely supported, which can lead to issues in older browsers or environments.
	+ Requires understanding of bitwise operations.

**Library and Special JS Feature**

The test case does not use any libraries. However, it relies on the `>>` operator, which is a right-shift operator that performs an unsigned right shift. This operation can be useful in certain situations, such as bit-level manipulation or optimizing performance-critical code.

**Other Considerations**

When writing this benchmark, consider the following:

* **Browser support**: Make sure to test your benchmark on multiple browsers and platforms to ensure consistency.
* **Sample size**: Use a sufficient sample size to get accurate results. In this case, the benchmark runs 17104962 times per second, which suggests that it may be using a high volume of data.
* **Context**: Be mindful of the context in which your code will run. For example, if you're running this benchmark on a mobile device or in a low-memory environment, consider the potential impact of over-optimization.

**Alternatives**

Other alternatives for rounding numbers include:

* Using the `Number.EPSILON` constant to determine the smallest representable value
* Implementing custom rounding functions using bitwise operations or other techniques
* Using a library like `decimal.js` for precise arithmetic

Note that each alternative has its own trade-offs and considerations, which may impact performance, readability, and maintainability.

Math.round vs Bitwise (version: 0)

Check is is faster using bitwise operations

Comparing performance of: `Math.round(n) vs Bitwise n + (n < 0 ? -0.5 : 0.5)>>0`

Created: 3 years ago by: Guest

Go to the latest result

Math.round(n)

Bitwise n + (n < 0 ? -0.5 : 0.5)>>0

Historical Performance Data aggregated from 8 community runs

Desktop Results:

Chrome 8 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

Math.round vs Bitwise (version: 0)

Check is is faster using bitwise operations

Comparing performance of: Math.round(n) vs Bitwise n + (n < 0 ? -0.5 : 0.5)>>0

Created: 3 years ago by: Guest

Go to the latest result

Math.round(n)

Bitwise n + (n < 0 ? -0.5 : 0.5)>>0

Historical Performance Data aggregated from 8 community runs

Desktop Results:

Chrome 8 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

Related benchmarks

Comparing performance of: `Math.round(n) vs Bitwise n + (n < 0 ? -0.5 : 0.5)>>0`