def test_zero_count(self):
lz = njit(lambda x: leading_zeros(x))
tz = njit(lambda x: trailing_zeros(x))
evens = [2, 42, 126, 128]
for T in types.unsigned_domain:
self.assertTrue(tz(T(0)) == lz(T(0)) == T.bitwidth)
for i in range(T.bitwidth):
val = T(2**i)
self.assertEqual(lz(val) + tz(val) + 1, T.bitwidth)
for n in evens:
self.assertGreater(tz(T(n)), 0)
self.assertEqual(tz(T(n + 1)), 0)
for T in types.signed_domain:
self.assertTrue(tz(T(0)) == lz(T(0)) == T.bitwidth)
for i in range(T.bitwidth - 1):
val = T(2**i)
self.assertEqual(lz(val) + tz(val) + 1, T.bitwidth)
self.assertEqual(lz(-val), 0)
self.assertEqual(tz(val), tz(-val))
for n in evens:
self.assertGreater(tz(T(n)), 0)
self.assertEqual(tz(T(n + 1)), 0)
def gcd(a, b):
"""
Stein's algorithm, heavily cribbed from Julia implementation.
"""
T = type(a)
if a == 0: return abs(b)
if b == 0: return abs(a)
za = trailing_zeros(a)
zb = trailing_zeros(b)
k = min(za, zb)
# Uses np.*_shift instead of operators due to return types
u = _unsigned(abs(np.right_shift(a, za)))
v = _unsigned(abs(np.right_shift(b, zb)))
while u != v:
if u > v:
u, v = v, u
v -= u
v = np.right_shift(v, trailing_zeros(v))
r = np.left_shift(T(u), k)
return r