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

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days 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.

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36

Browser/OS: Chrome 124 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Or bitwise	5109393.0 Ops/sec
Double bitwise not	5486190.0 Ops/sec
Left bitwise shift	5602581.0 Ops/sec
Math.round	3147739.0 Ops/sec

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 26 days ago):