Benchmark: Truncation Methods

Script Preparation code:

var a = Array.from({length: 10000}, _ => Math.random() * 1000);

Tests:

Bitwise complement
a.map(i => ~~i);
Bitwise shift
a.map(i => i >>> 0);
Math.trunc()
a.map(i => Math.trunc(i));
Math.round()
a.map(i => Math.round(i));

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Bitwise complement
Bitwise shift
Math.trunc()
Math.round()

Fastest: N/A

Slowest: N/A

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and benchmark preparation code.

**Benchmark Definition**

The benchmark is designed to test various methods for truncating a number to an integer. This is achieved by creating an array of 10,000 random numbers between 0 and 1000, and then applying different methods to truncate these numbers.

**Script Preparation Code**

The script preparation code creates an array `a` with 10,000 elements, each containing a random value between 0 and 1000. The `_` variable is likely a shorthand for the arrow function parameter.

```javascript
var a = Array.from({length: 10000}, _ => Math.random() * 1000);
```

**Individual Test Cases**

There are four test cases, each with its own benchmark definition:

1. `a.map(i => ~~i);`: This uses the bitwise complement operator (`~~`) to truncate the number.
2. `a.map(i => i >>> 0);`: This uses the bitwise shift operator (`>>>`) to truncate the number.
3. `a.map(i => Math.trunc(i));`: This uses the `Math.trunc()` function to truncate the number.
4. `a.map(i => Math.round(i));`: This uses the `Math.round()` function to truncate the number.

Let's briefly describe each approach:

* **Bitwise complement (`~~i`)**: This method is not as straightforward as it seems. The bitwise complement operator flips all the bits of a number, which can lead to incorrect results for negative numbers. For example, `-5` becomes `1` when using this method.
* **Bitwise shift (`i >>> 0`)**: This method works by shifting the bits of the number to the right and then using the least significant bit as the truncated value. This approach is more straightforward but can be slower than other methods for large numbers.
* **Math.trunc()**: This function returns the largest possible integer less than or equal to the input value. It is a standard JavaScript function that uses a combination of bit manipulation and rounding algorithms to produce accurate results.
* **Math.round()**: This function returns the closest integer to the input value, which can lead to incorrect results for non-integer values. In this benchmark, it's used to test the truncation behavior.

**Pros and Cons**

* **Bitwise complement (`~~i`)**: Pros: simple to implement, cons: can produce incorrect results for negative numbers.
* **Bitwise shift (`i >>> 0`)**: Pros: straightforward, cons: slower for large numbers.
* **Math.trunc()**: Pros: accurate, consistent, and well-tested. Cons: might be slower than other methods due to its internal algorithm.
* **Math.round()**: Pros: simple to implement, cons: can produce incorrect results for non-integer values.

**Library**

None of the individual test cases rely on external libraries.

**Special JS feature or syntax**

The bitwise shift operator (`>>>`) is a special JavaScript operator that shifts the bits of a number to the right and then uses the least significant bit as the truncated value. This approach is specific to JavaScript and is not commonly used in other programming languages.

**Alternatives**

Other methods for truncating numbers include:

* `Math.floor()`: Returns the largest possible integer less than or equal to the input value.
* `Number.EPSILON`: A small value that can be added to a number before taking its floor value, effectively "rounding down".
* Custom implementations using bit manipulation and arithmetic operations.

Note that these alternatives might not be included in the benchmark as they are not as straightforward or well-tested as the methods used in this benchmark.

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36

Browser/OS: Chrome 114 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Bitwise complement	39170.0 Ops/sec
Bitwise shift	39852.3 Ops/sec
Math.trunc()	1595.5 Ops/sec
Math.round()	1456.4 Ops/sec

Related benchmarks:

Truncation Methods (version: 0)

Testing the various methods for truncating a number to an integer

Comparing performance of: Bitwise complement vs Bitwise shift vs Math.trunc() vs Math.round()

Created: one year ago by: Guest

Jump to the latest result

Bitwise complement

Bitwise shift

Math.trunc()

Math.round()

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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