examples.py

"""Benchmark programs offered as one-click presets.

Each is chosen to be a fair test of translation rather than a trick: pure
computation, deterministic output, no I/O or third-party imports, and a runtime
long enough in Python that the speedup is unambiguous.

The output is printed so the two languages can be compared exactly - a
translation that is fast but wrong is a failed translation.
"""

MAX_SUBARRAY = '''# Brute-force maximum subarray sum over a seeded pseudo-random sequence.
# O(n^2) by design - the interesting question is whether the model preserves
# the algorithm or silently upgrades it.

def lcg(seed, a=1664525, c=1013904223, m=2**32):
    value = seed
    while True:
        value = (a * value + c) % m
        yield value

def max_subarray_sum(n, seed, min_val, max_val):
    lcg_gen = lcg(seed)
    random_numbers = [next(lcg_gen) % (max_val - min_val + 1) + min_val for _ in range(n)]
    max_sum = float('-inf')
    for i in range(n):
        current_sum = 0
        for j in range(i, n):
            current_sum += random_numbers[j]
            if current_sum > max_sum:
                max_sum = current_sum
    return max_sum

def total_max_subarray_sum(n, initial_seed, min_val, max_val):
    total_sum = 0
    lcg_gen = lcg(initial_seed)
    for _ in range(20):
        seed = next(lcg_gen)
        total_sum += max_subarray_sum(n, seed, min_val, max_val)
    return total_sum

n = 10000
initial_seed = 42
min_val = -10
max_val = 10

import time
start_time = time.time()
result = total_max_subarray_sum(n, initial_seed, min_val, max_val)
end_time = time.time()

print("Total Maximum Subarray Sum (20 runs):", result)
print("Execution Time: {:.6f} seconds".format(end_time - start_time))
'''

PI_LEIBNIZ = '''# Tight floating-point loop. Almost pure interpreter overhead in Python,
# so it shows the raw cost of dynamic dispatch per iteration.

import time

def calculate(iterations, param1, param2):
    result = 1.0
    for i in range(1, iterations + 1):
        j = i * param1 - param2
        result -= (1 / j)
        j = i * param1 + param2
        result += (1 / j)
    return result

start_time = time.time()
result = calculate(100_000_000, 4, 1) * 4
end_time = time.time()

print(f"Result: {result:.12f}")
print(f"Execution Time: {end_time - start_time:.6f} seconds")
'''

PRIME_SIEVE = '''# Sieve of Eratosthenes plus a digit-sum reduction.
# Memory-bound rather than compute-bound, so it stresses a different axis
# than the other two.

import time

def sieve(limit):
    flags = [True] * (limit + 1)
    flags[0] = flags[1] = False
    p = 2
    while p * p <= limit:
        if flags[p]:
            for multiple in range(p * p, limit + 1, p):
                flags[multiple] = False
        p += 1
    return flags

def digit_sum(n):
    total = 0
    while n:
        total += n % 10
        n //= 10
    return total

start_time = time.time()
limit = 5_000_000
flags = sieve(limit)
count = 0
checksum = 0
for n in range(limit + 1):
    if flags[n]:
        count += 1
        checksum += digit_sum(n)
end_time = time.time()

print(f"Primes below {limit}: {count}")
print(f"Digit-sum checksum: {checksum}")
print(f"Execution Time: {end_time - start_time:.6f} seconds")
'''

COLLATZ = '''# Longest Collatz chain below a bound. Unpredictable branching, which
# defeats naive vectorisation and rewards a good compiler.

import time

def chain_length(n):
    steps = 0
    while n != 1:
        n = n // 2 if n % 2 == 0 else 3 * n + 1
        steps += 1
    return steps

start_time = time.time()
limit = 1_000_000
best_n = 0
best_len = 0
for n in range(1, limit):
    length = chain_length(n)
    if length > best_len:
        best_len = length
        best_n = n
end_time = time.time()

print(f"Longest Collatz chain below {limit}: n={best_n} with {best_len} steps")
print(f"Execution Time: {end_time - start_time:.6f} seconds")
'''

EXAMPLES: dict[str, str] = {
    "Maximum subarray sum (O(n^2))": MAX_SUBARRAY,
    "Pi via Leibniz series (100M iterations)": PI_LEIBNIZ,
    "Prime sieve + digit sums (5M)": PRIME_SIEVE,
    "Longest Collatz chain (1M)": COLLATZ,
}

DEFAULT_EXAMPLE = "Maximum subarray sum (O(n^2))"