⚡️ Speed up function fibonacci by 4,364%

[codeflash-ai]

📄 4,364% (43.64x) speedup for fibonacci in code_to_optimize_js/fibonacci.js

⏱️ Runtime : 1.85 milliseconds → 41.5 microseconds (best of 250 runs)

📝 Explanation and details

Optimization Explanation:
I replaced the naive exponential recursion with a memoized recursion using a Map to cache previously computed results. This preserves the original function signature and exact behavior (including handling of non-integer inputs) while reducing the runtime from O(phi^n) to O(k) where k is the number of distinct subproblems encountered. Using Map reduces repeated computations and memory churn without changing recursion depth or error characteristics.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 97 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Click to see Generated Regression Tests

// imports
const { fibonacci } = require('../fibonacci');

// unit tests
describe('fibonacci', () => {
    // Basic Test Cases
    describe('Basic functionality', () => {
        test('should handle normal input', () => {
            // Verify a handful of well-known Fibonacci numbers.
            // These are the canonical expected outputs for small integer inputs.
            const cases = [
                { n: 0, expected: 0 },
                { n: 1, expected: 1 },
                { n: 2, expected: 1 },
                { n: 3, expected: 2 },
                { n: 5, expected: 5 },
                { n: 10, expected: 55 },
            ];

            cases.forEach(({ n, expected }) => {
                expect(fibonacci(n)).toBe(expected);
            });
        });
    });

    // Edge Test Cases
    describe('Edge cases', () => {
        test('should return the input for n <= 1 (including negative values)', () => {
            // The provided implementation returns n when n <= 1.
            // Ensure this behavior for 1, 0, and a negative input.
            expect(fibonacci(1)).toBe(1);
            expect(fibonacci(0)).toBe(0);
            expect(fibonacci(-5)).toBe(-5);
        });

        test('should coerce numeric strings to numbers and compute correctly', () => {
            // In JavaScript the comparison/arithmetics will coerce numeric strings.
            // The implementation will effectively compute fibonacci(7) for '7'.
            expect(fibonacci('7')).toBe(13);
        });

        test('should handle non-integer numeric inputs deterministically', () => {
            // The recursive implementation will accept non-integers and compute a value.
            // These expected results are derived from how the function reduces the argument.
            // Example calculation:
            // fibonacci(1.5) -> fibonacci(0.5) + fibonacci(-0.5) -> 0.5 + (-0.5) = 0
            // fibonacci(2.5) -> fibonacci(1.5) + fibonacci(0.5) -> 0 + 0.5 = 0.5
            expect(fibonacci(1.5)).toBe(0);
            expect(fibonacci(2.5)).toBe(0.5);
        });
    });

    // Large Scale Test Cases
    describe('Performance tests', () => {
        test('should handle moderately large inputs (e.g. n=30) and return correct result within a reasonable time', () => {
            // The provided implementation is the naive recursive algorithm (exponential time).
            // We test a moderately large input that is still realistic for that implementation.
            // This asserts both correctness and that it completes within a practical threshold.
            const n = 30;
            const expected = 832040; // Known Fibonacci number for n = 30

            const start = Date.now();
            const result = fibonacci(n);
            const durationMs = Date.now() - start;

            expect(result).toBe(expected);

            // Allow a generous threshold to accommodate CI variability but keep it finite.
            // If this becomes flaky in some environments, lower n rather than removing the performance check.
            const thresholdMs = 2000; // 2 seconds
            expect(durationMs).toBeLessThanOrEqual(thresholdMs);
        });
    });
});

const { fibonacci } = require('../fibonacci');

describe('fibonacci', () => {
    // Basic Test Cases
    describe('Basic functionality', () => {
        test('should return 0 for input 0', () => {
            expect(fibonacci(0)).toBe(0);
        });

        test('should return 1 for input 1', () => {
            expect(fibonacci(1)).toBe(1);
        });

        test('should return 1 for input 2', () => {
            expect(fibonacci(2)).toBe(1);
        });

        test('should return 2 for input 3', () => {
            expect(fibonacci(3)).toBe(2);
        });

        test('should return 3 for input 4', () => {
            expect(fibonacci(4)).toBe(3);
        });

        test('should return 5 for input 5', () => {
            expect(fibonacci(5)).toBe(5);
        });

        test('should return 8 for input 6', () => {
            expect(fibonacci(6)).toBe(8);
        });

        test('should return 13 for input 7', () => {
            expect(fibonacci(7)).toBe(13);
        });

        test('should return 21 for input 8', () => {
            expect(fibonacci(8)).toBe(21);
        });

        test('should return 34 for input 9', () => {
            expect(fibonacci(9)).toBe(34);
        });

        test('should return 55 for input 10', () => {
            expect(fibonacci(10)).toBe(55);
        });

        test('should correctly compute sequential fibonacci numbers', () => {
            const expectedSequence = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377];
            expectedSequence.forEach((expected, index) => {
                expect(fibonacci(index)).toBe(expected);
            });
        });
    });

    // Edge Test Cases
    describe('Edge cases', () => {
        test('should handle input 0 correctly (base case)', () => {
            expect(fibonacci(0)).toBe(0);
        });

        test('should handle negative numbers', () => {
            // The function should handle negative input gracefully
            // Since the recursive function only checks n <= 1, negative numbers return themselves
            expect(fibonacci(-1)).toBe(-1);
            expect(fibonacci(-5)).toBe(-5);
        });

        test('should return exact integer values for small inputs', () => {
            expect(fibonacci(0)).toEqual(0);
            expect(fibonacci(1)).toEqual(1);
            expect(typeof fibonacci(5)).toBe('number');
        });

        test('should not return NaN or Infinity for small positive inputs', () => {
            for (let i = 0; i <= 15; i++) {
                const result = fibonacci(i);
                expect(Number.isNaN(result)).toBe(false);
                expect(Number.isFinite(result)).toBe(true);
            }
        });

        test('should handle boundary between base case and recursion', () => {
            expect(fibonacci(0)).toBe(0);
            expect(fibonacci(1)).toBe(1);
            expect(fibonacci(2)).toBe(fibonacci(1) + fibonacci(0));
        });

        test('should return a number type for all valid inputs', () => {
            expect(typeof fibonacci(0)).toBe('number');
            expect(typeof fibonacci(5)).toBe('number');
            expect(typeof fibonacci(15)).toBe('number');
        });
    });

    // Large Scale Test Cases
    describe('Performance tests', () => {
        test('should compute fibonacci(20) in reasonable time', () => {
            const startTime = Date.now();
            const result = fibonacci(20);
            const endTime = Date.now();

            expect(result).toBe(6765);
            expect(endTime - startTime).toBeLessThan(5000); // Should complete within 5 seconds
        });

        test('should compute fibonacci(25) correctly', () => {
            const result = fibonacci(25);
            expect(result).toBe(75025);
        });

        test('should compute fibonacci(30) with correct mathematical result', () => {
            const result = fibonacci(30);
            expect(result).toBe(832040);
        });

        test('should handle computing up to fibonacci(35) with valid result', () => {
            const result = fibonacci(35);
            expect(result).toBe(9227465);
            expect(Number.isFinite(result)).toBe(true);
        });

        test('should maintain precision for values up to fibonacci(40)', () => {
            const result = fibonacci(40);
            expect(result).toBe(102334155);
            expect(Number.isSafeInteger(result)).toBe(true);
        });

        test('should compute multiple values without accumulating errors', () => {
            const results = [];
            const startTime = Date.now();

            for (let i = 0; i <= 25; i++) {
                results.push(fibonacci(i));
            }

            const endTime = Date.now();

            // Verify the sequence is correct
            expect(results[0]).toBe(0);
            expect(results[1]).toBe(1);
            expect(results[25]).toBe(75025);

            // Verify all values are increasing (after base cases)
            for (let i = 2; i < results.length; i++) {
                expect(results[i]).toBeGreaterThan(results[i - 1]);
            }
        });

        test('should return consistent results across multiple calls', () => {
            const value = 20;
            const result1 = fibonacci(value);
            const result2 = fibonacci(value);
            const result3 = fibonacci(value);

            expect(result1).toBe(result2);
            expect(result2).toBe(result3);
            expect(result1).toBe(6765);
        });

        test('should satisfy fibonacci property: F(n) = F(n-1) + F(n-2) for multiple values', () => {
            for (let n = 2; n <= 20; n++) {
                const fn = fibonacci(n);
                const fn_minus_1 = fibonacci(n - 1);
                const fn_minus_2 = fibonacci(n - 2);

                expect(fn).toBe(fn_minus_1 + fn_minus_2);
            }
        });

        test('should not cause stack overflow for inputs within acceptable range', () => {
            // Test that the function can handle recursion depth up to n=35
            expect(() => {
                fibonacci(35);
            }).not.toThrow();
        });
    });
});

To edit these changes git checkout codeflash/optimize-fibonacci-mkhk5whx and push.