Benchmark: divide by 2 vs multiply by 0.5

Script Preparation code:

const length = 100000;
const tmp_nums=[];
for (let i = 0; i < length; i++) {
  tmp_nums.push(Date.now() + Math.random());
}
nums = [...tmp_nums];
nums_len = length;

Tests:

div by 2
const length = nums_len; for (let i = 0; i < length; i++) { nums[i] /= 2; }
div by 2.0
const length = nums_len; for (let i = 0; i < length; i++) { nums[i] /= 2.0; }
multiply by 0.5
const length = nums_len; for (let i = 0; i < length; i++) { nums[i] *= 0.5; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
div by 2
div by 2.0
multiply by 0.5

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/134.0.0.0 Mobile Safari/537.36 OPR/88.0.0.0

Browser/OS: Opera Mobile 88 on Android

View result in a separate tab

Test name	Executions per second
div by 2	1914.3 Ops/sec
div by 2.0	2733.6 Ops/sec
multiply by 0.5	2813.6 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 benchmark and explain what's being tested, compared, and the pros/cons of each approach.

**Benchmark Overview**

The benchmark is designed to measure the performance difference between dividing an array by 2 (using the `/=` operator) and multiplying it by 0.5 (using the `*` operator). The test case uses JavaScript, a dynamically-typed language that can be prone to issues with precision and rounding.

**Script Preparation Code**

The script preparation code generates an array of random numbers using the `Date.now()` function and stores them in the `nums` variable. It also creates a copy of this array and assigns it to the `tmp_nums` variable, which is not used in the benchmarking process.

```javascript
const length = 100000;
const tmp_nums = [];
for (let i = 0; i < length; i++) {
  tmp_nums.push(Date.now() + Math.random());
}
nums = [...tmp_nums];
nums_len = length;
```

**Html Preparation Code**

There is no HTML preparation code provided, which means that the benchmarking process does not involve any asynchronous operations or external dependencies.

**Individual Test Cases**

The three test cases are designed to measure the performance of each operation:

1. `div by 2`: Divides the `nums` array by 2 using the `/=` operator.
```javascript
const length = nums_len;
for (let i = 0; i < length; i++) {
  nums[i] /= 2;
}
```

2. `div by 2.0`: Divides the `nums` array by 2.0 using a decimal literal, which can introduce precision issues.
```javascript
const length = nums_len;
for (let i = 0; i < length; i++) {
  nums[i] /= 2.0;
}
```

3. `multiply by 0.5`: Multiplies the `nums` array by 0.5 using the `*` operator.
```javascript
const length = nums_len;
for (let i = 0; i < length; i++) {
  nums[i] *= 0.5;
}
```

**Library and Special JS Features**

The benchmark uses no external libraries, but it does use the `Math.random()` function to generate random numbers.

There is no special JavaScript feature or syntax used in this benchmark.

**Pro/Cons Comparison**

| Operation | Pros | Cons |
| --- | --- | --- |
| Division by 2 (`/=`) | Can be faster due to caching | May introduce precision issues with floating-point arithmetic |
| Multiplication by 0.5 (`*`) | Typically faster than division for large numbers | May not cache as effectively as division, leading to slower performance |
| Division by 2.0 (`/=` with decimal literal) | Not recommended due to potential precision issues | Slower than traditional division due to extra arithmetic operations |

**Other Alternatives**

If you wanted to measure the performance of these operations without using `Math.random()`, you could use a fixed seed for the random number generator or create an array of pre-generated numbers. You could also consider using a different method to generate the random numbers, such as using a cryptographically secure pseudo-random number generator.

Additionally, if you wanted to measure the performance of these operations with more precision, you could use a library like `big.js` that provides support for arbitrary-precision arithmetic.

For production code, it is generally recommended to avoid using `/=` with decimal literals and instead use multiplication or division with explicit decimal literals (e.g., `0.5`) to ensure accurate results.

Related benchmarks:

divide by 2 vs multiply by 0.5 (version: 0)

Comparing performance of: div by 2 vs div by 2.0 vs multiply by 0.5

Created: 4 years ago by: Guest

Jump to the latest result

div by 2

div by 2.0

multiply by 0.5

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):