Benchmark: loop length recalculation

Script Preparation code:

  var arr=new Array(1000000)

Tests:

normal loop
for (var i=0;i<arr.length;i++){val=arr[i]}
loop without length
var l=arr.length; for (var i=0;i<l;i++){val=arr[i]}
reverse loop
for (var i=arr.length;i>0;i--){val=arr[i]}
weird trick
for (var i=arr.length;i>0;i--){val=arr[i]|0}

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
normal loop
loop without length
reverse loop
weird trick

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and its components.

**Benchmark Definition JSON**

The benchmark definition JSON contains four main pieces of information:

*   `Name`: The name of the benchmark, which is "loop length recalculation".
*   `Description`: This field is empty in this case, but it usually provides a brief description of what the benchmark is testing.
*   `Script Preparation Code` and `Html Preparation Code`: These fields specify any necessary setup code for the benchmark. In this case, there's only script preparation code, which initializes an array with 1 million elements using `var arr = new Array(1000000)`.

**Individual Test Cases**

The benchmark defines four individual test cases:

*   **Test Case 1: Normal Loop**
    *   Benchmark Definition: `for (var i=0;i<arr.length;i++){val=arr[i]}`
    *   Purpose: This is a standard for loop that accesses each element in the array using its index.
*   **Test Case 2: Loop Without Length**
    *   Benchmark Definition: `var l=arr.length;\r\nfor (var i=0;i<l;i++){val=arr[i]}`
    *   Purpose: This test case uses a variable `l` to store the length of the array and then uses this value in the loop condition. This approach can be faster than accessing `arr.length` directly because it avoids a potential property lookup or getter call.
*   **Test Case 3: Reverse Loop**
    *   Benchmark Definition: `for (var i=arr.length;i>0;i--){val=arr[i]}`
    *   Purpose: This test case uses a decrementing loop counter to iterate from the last element to the first. This approach can be faster than the traditional forward loop because it reduces the number of array accesses.
*   **Test Case 4: Weird Trick**
    *   Benchmark Definition: `for (var i=arr.length;i>0;i--){val=arr[i]|0}`
    *   Purpose: This test case uses a bitwise OR operation (`|0`) to cast the array element to an integer. The purpose of this trick is unclear, and it may be intended to optimize the loop or demonstrate some other effect.

**Library Used**

There is no explicit library mentioned in the benchmark definition or individual test cases. However, the use of `var` instead of `let` or `const` for declaring variables might indicate a compatibility mode with older browsers.

**Special JavaScript Feature or Syntax**

There are no special features or syntax used in these test cases that would require specific knowledge to understand. The focus is on comparing different loop approaches and their potential performance implications.

**Alternatives**

Other alternatives could be explored when optimizing loops:

*   **Using `Array.prototype.forEach()`**: This method can eliminate the need for explicit loop counters and array indexing.
*   **Using a custom iterator**: If you're working with a large dataset or performance-critical code, you might consider implementing a custom iterator to iterate over the data more efficiently.
*   **Using SIMD instructions**: For certain types of loops that involve vectorized operations (e.g., matrix multiplication), using SIMD (Single Instruction, Multiple Data) instructions can provide significant performance improvements.

However, for simple array iteration like in these test cases, the differences between these alternatives might be negligible or not worth exploring.

Related benchmarks:

loop length recalculation (version: 0)

Comparing performance of: normal loop vs loop without length vs reverse loop vs weird trick

Created: 8 years ago by: Guest

Jump to the latest result

normal loop

loop without length

reverse loop

weird trick

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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