Benchmark: Round in javascript

Script Preparation code:

var somenum = 7.3, rounded;

Tests:

Or bitwise
rounded = (0.5 + somenum) | 0;
Double bitwise not
rounded = ~~ (0.5 + somenum);
Left bitwise shift
rounded = (0.5 + somenum) << 0;
Math.round
rounded = Math.round(somenum);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Or bitwise
Double bitwise not
Left bitwise shift
Math.round

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 27 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/136.0.0.0 Safari/537.36

Browser/OS: Chrome 136 on Windows

View result in a separate tab

Test name	Executions per second
Or bitwise	5587303.5 Ops/sec
Double bitwise not	5582126.5 Ops/sec
Left bitwise shift	6439524.0 Ops/sec
Math.round	7427132.5 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll break down the provided JSON and explain what's being tested, compared, and the pros and cons of different approaches.

**Benchmark Definition**

The benchmark definition is a simple JavaScript expression that calculates the rounded value of `somenum` (a constant with value 7.3) using different methods:

1. `rounded = (0.5 + somenum) | 0;` - This uses the bitwise OR operator (`|`) to truncate the result to an integer.
2. `rounded = ~~ (0.5 + somenum);` - This uses the bitwise NOT operator (`~~`) to perform a signed integer arithmetic and then truncates the result to an integer.
3. `rounded = (0.5 + somenum) << 0;` - This uses the left shift operator (`<<`) with a shift amount of 0, effectively doing nothing, but is included for completeness.
4. `rounded = Math.round(somenum);` - This uses the built-in `Math.round()` function to calculate the rounded value.

**Test Cases**

Each test case represents a single execution of one of these expressions. The options being compared are:

1. **Or bitwise**: `(0.5 + somenum) | 0;`
	* Pros: Simple and efficient, works for positive and negative numbers.
	* Cons: May produce unexpected results for very large or small inputs due to integer overflows.
2. **Double bitwise not**: `~~ (0.5 + somenum);`
	* Pros: Works with both positive and negative numbers, handles integer overflows by converting to a signed integer.
	* Cons: The `~~` operator can be confusing for some developers, as it's not immediately clear what it does.
3. **Left bitwise shift**: `(0.5 + somenum) << 0;`
	* Pros: Does not affect the result of the calculation (effectively a no-op), handles all inputs correctly.
	* Cons: The left shift operator is being used in an unusual way, which might be confusing for some developers.
4. **Math.round**: `Math.round(somenum);`
	* Pros: Standard and well-documented function, handles all inputs correctly.
	* Cons: May be slower than other methods due to the overhead of a function call.

**Library Usage**

There are no explicit libraries being used in these test cases.

**Special JavaScript Features or Syntax**

None of the provided expressions use any special JavaScript features or syntax (e.g., async/await, arrow functions, etc.).

**Alternatives**

Other alternatives for rounding numbers in JavaScript include:

1. `Number.round()`: This is a non-standard function that was available in older versions of JavaScript but has been deprecated.
2. `Float32Array.prototype.round()`: This uses the `Float32Array` data type to perform rounding operations, which can be more efficient than using the `Math.round()` function.

In summary, the benchmark tests four different methods for rounding numbers in JavaScript: or bitwise, double bitwise not, left bitwise shift, and Math.round. Each method has its pros and cons, and some might be more suitable for specific use cases or performance requirements.

Related benchmarks:

Round in javascript (version: 0)

Comparing performance of: Or bitwise vs Double bitwise not vs Left bitwise shift vs Math.round

Created: 4 years ago by: Guest

Jump to the latest result

Or bitwise

Double bitwise not

Left bitwise shift

Math.round

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):