Exploiting Constraints for Significant Performance Gains: Optimizing Even Number Counting in C++
2025-03-09
This article explores optimizing the performance of counting even numbers in a uint8_t array in C++. By comparing two approaches—using `std::count_if` and a custom counting function—the author demonstrates that the custom function, leveraging the constraint that the number of even values is between 0 and 255, significantly improves performance, achieving up to a 9.5x speedup in tests. The article analyzes the assembly code generated by both methods, explaining the performance difference, and mentions a vectorization issue in specific GCC versions.