The Weird Concept of Branchless Programming
4 hours ago
- #branchless
- #optimization
- #performance
- Modern CPUs use branch predictors to guess execution paths, but mispredictions can cause significant performance penalties.
- Branchless programming avoids conditional jumps by using arithmetic and bit operations, improving performance in unpredictable scenarios.
- A branch in code is a conditional execution path (if, elif, else), which translates to jump instructions in machine code.
- Branchless techniques are crucial for performance-critical or side-channel-resistant applications, such as cryptography.
- Three examples of branchless programming are provided: absolute value (abs), clamping (clamp), and partitioning (partition).
- The absolute value example demonstrates using bit manipulation to avoid branches.
- Clamping ensures a value stays within a range without conditional checks, useful in simulations and rendering.
- Partitioning an array branchlessly improves performance by avoiding unpredictable branches in loops.
- Benchmark results show that branchless partitioning can be 1.2x faster than the branchy version, while abs and clamp show negligible differences.
- Branchless programming is a precise optimization tool, offering performance benefits when used appropriately.