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