Add primes/Atkin benchmark in C

[arshitas]

Summary

Implements primes/Atkin benchmark in C.

Checklist

Please review CONTRIBUTING.md for detailed guidelines.

• Studied reference implementations (PHP, C++, or Python)
• Implementation uses exact same logic as references (no optimizations)
• File placed in correct directory: langs/<language>/<algorithm>/<Name>.<ext>
• Added to benchmark.yml in language directory
• README.md implementation table updated (❌ → ✅)
• Tested locally with Docker
• Commit follows format: feat(<language>): add <algorithm>/<Name> benchmark

Verification

Example:

• Compared loop structures with langs/php/primes/Simple.php
• Verified same array operations as C++ reference
• Tested output matches expected results

Notes

Original Description

Implement Sieve of Atkins algorithm in C for benchmark suite

Output:
[323381, 323383, 3233803, 3233809, 3233851, 3233863, 3233873, 3233887, 3233897]
Execution time: 236.57ms

=== Code Execution Successful ===

[arshitas]

Resolves issue #78

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 3 comments.

[Copilot]

Memory leak: head no longer points to the tree root after the loop on lines 229-237. Only the subtree from head downward is freed here, not the entire tree. The tree root should be stored separately and freed here.

To fix this, use the same pattern suggested in the previous comment - store the root separately:

Node *root = generate_tree(primes, prime_count);
// ... rest of code ...
Node_free(root);  // Free the entire tree, not just the subtree

[Copilot]

Performance issue: strlen(buffer) is called on every iteration of the loop. Since the buffer content doesn't change during the loop, this should be computed once before the loop.

Change to:

size_t buffer_len = strlen(buffer);
for (int j = 0; j < buffer_len; ++j) {

Suggested change

	for (int j = 0; j < strlen(buffer); ++j) {
	size_t buffer_len = strlen(buffer);
	for (int j = 0; j < buffer_len; ++j) {

[leon0399]

Supposedly matches the behavior of other benchmarks

[Copilot]

Potential null pointer dereference: If find returns NULL (when the prefix is not found), to_string will be called with a NULL pointer, which will cause undefined behavior.

Add a null check:

int *result = find(UPPER_BOUND, PREFIX, &result_size);
if (result == NULL) {
    printf("[]\n");
    printf("Execution time: 0.00ms\n");
    return 0;
}

Suggested change

	if (result == NULL) {
	printf("[]\n");
	printf("Execution time: 0.00ms\n");
	return 0;
	}

[leon0399]

Execution time must be actual if this is added