gistfile1.txt

def f_iterative(x):
    stack = [(x, 0)]  # (参数, 状态): 0=初始, 1=等待内层f(x-0.5), 2=等待外层f(x-f(x-0.5))
    results = {}  # 缓存中间结果，避免重复计算
    
    while stack:
        x, state = stack.pop()
        
        if x < 0:
            results[x] = -x
            continue
            
        if state == 0:
            # 初始状态，计算f(x-0.5)
            stack.append((x, 1))
            if x - 0.5 not in results:
                stack.append((x - 0.5, 0))
        elif state == 1:
            # 已得到f(x-0.5)，计算f(x - f(x-0.5))
            inner_result = results.get(x - 0.5)
            next_x = x - inner_result
            stack.append((x, 2))
            if next_x not in results:
                stack.append((next_x, 0))
        elif state == 2:
            # 已得到外层结果，计算0.5 * f(next_x)
            inner_result = results.get(x - results.get(x - 0.5))
            results[x] = 0.5 * inner_result
    
    return results[x]

def g(x):
    import math
    f_x = f_iterative(x)
    return -math.log2(f_x) if f_x > 0 else float('inf')

# 计算g(4) mod 4
try:
    result = g(4) % 4
    print(result)
except RecursionError:
    print("Recursion depth exceeded")