Function py_factorial

Lib/test/test_math_integer.py:57–66

Factorial of nonnegative integer n, via "Binary Split Factorial Formula" described at http://www.luschny.de/math/factorial/binarysplitfact.html

(n)

        return partial_product(start, mid) * partial_product(mid, stop)

def py_factorial(n):
    """Factorial of nonnegative integer n, via "Binary Split Factorial Formula"
    described at http://www.luschny.de/math/factorial/binarysplitfact.html

    """
    inner = outer = 1
    for i in reversed(range(n.bit_length())):
        inner *= partial_product((n >> i + 1) + 1 | 1, (n >> i) + 1 | 1)
        outer *= inner
    return outer << (n - count_set_bits(n))


class IntMathTests(unittest.TestCase):