cython

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# mode: run
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# Test longintrepr declarations by implementing a simple function
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from cpython.longintrepr cimport *
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cimport cython
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@cython.cdivision(True)
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def lshift(long a, unsigned long n):
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    """
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    Return a * 2^n as Python long.
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    >>> print(lshift(3, 1))
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    6
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    >>> print(lshift(1, 30))
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    1073741824
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    >>> print(lshift(-12345, 115))
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    512791237748899576593671817473776680960
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    >>> print(-12345 << 115)
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    -512791237748899576593671817473776680960
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    >>> [i for i in range(100) if (65535 << i) != lshift(65535, i)]
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    []
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    >>> print(lshift(0, 12345))
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    0
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    >>> print(lshift(2**62, 0))   # doctest: +ELLIPSIS
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    Traceback (most recent call last):
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    ...
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    OverflowError...
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    """
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    if not a:
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        return _PyLong_New(0)
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    cdef unsigned long apos = a if a > 0 else -a
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    if (apos >> 1) >= <unsigned long>PyLong_BASE:
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        raise OverflowError
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    cdef unsigned long index = n // PyLong_SHIFT
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    cdef unsigned long shift = n % PyLong_SHIFT
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    cdef digit d = apos
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    cdef digit low = (d << shift) & PyLong_MASK
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    cdef digit high = (d >> (PyLong_SHIFT - shift))
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    if high == 0:
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        ret = _PyLong_New(index + 1)
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        ret.ob_digit[index] = low
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    else:
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        ret = _PyLong_New(index + 2)
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        ret.ob_digit[index] = low
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        ret.ob_digit[index + 1] = high
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    while index >= 1:
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        index -= 1
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        ret.ob_digit[index] = 0
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    return ret
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