⚡️ Speed up method Algorithms.fibonacci by 12%

[codeflash-ai]

📄 12% (0.12x) speedup for Algorithms.fibonacci in code_to_optimize/java/src/main/java/com/example/Algorithms.java

⏱️ Runtime : 4.37 milliseconds → 3.88 milliseconds (best of 5 runs)

📝 Explanation and details

This optimization achieves a 12% runtime improvement (from 4.37ms to 3.88ms) by streamlining the bit-scanning loop in the fast-doubling Fibonacci algorithm.

Key Change:
The original code computed (n >>> i) & 1 on every iteration, requiring two operations: a right-shift of n by i bits, then a bitwise AND. The optimized version precomputes a bitmask (mask = 1 << highestBit) and shifts only the mask right each iteration (mask >>>= 1), checking bits via (n & mask) == 0.

Why This is Faster:

1. Reduced shift operations per iteration: Instead of shifting the potentially large value n right by varying amounts each loop iteration, we shift a single-bit mask (always a power of 2) right by one position. Shifting a mask is cheaper than repeatedly shifting n.
2. Simpler bit extraction: The mask directly isolates the current bit position in n without needing to shift n itself, reducing instruction complexity in the hot loop.
3. Better CPU pipelining: The mask-based approach produces more predictable shift patterns (always >>>= 1), which modern CPUs can optimize more effectively than variable-distance shifts.

Impact:
The fast-doubling algorithm processes each bit of n exactly once (from MSB to LSB), so for Fibonacci numbers at position n, the loop runs ⌊log₂(n)⌋ + 1 times. This optimization reduces the per-iteration overhead by eliminating the variable right-shift of n, yielding measurable speedup especially for larger n values where the loop iterates more times. The 12% improvement demonstrates that even small reductions in tight loop overhead compound significantly across iterations.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	✅ 12 Passed
🌀 Generated Regression Tests	🔘 None Found
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

⚙️ Click to see Existing Unit Tests

To edit these changes git checkout codeflash/optimize-Algorithms.fibonacci-mlbhxpv8 and push.