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"""
This file contains some little tricks and verifications for some code which
is used in the C implementation of bitarray.
"""
from random import randint
import unittest
# ---------------------------- Range checks ---------------------------------
class RangeTests(unittest.TestCase):
def test_check_simple(self):
r = range(0, 256)
for k in range(-10, 300):
self.assertEqual(k < 0 or k > 0xff, bool(k >> 8))
self.assertEqual(k not in r, bool(k >> 8))
def test_check(self):
# used in various places in C code
for i in range(0, 11):
m = 1 << i
for k in range(-10, 2000):
res1 = k not in range(0, m)
res2 = k < 0 or k >= m
self.assertEqual(res1, res2)
# simply shift i to right and see if anything remains
res3 = bool(k >> i)
self.assertEqual(res1, res3)
def test_check_2(self):
# this is used in _util.c in set_count()
for i in range(0, 11):
m = 1 << i
for k in range(-10, 2000):
res1 = k not in range(0, m + 1)
res2 = k < 0 or k > m
self.assertEqual(res1, res2)
# same as above but combined with k substracted by 1
res3 = bool(k >> i) and bool((k - 1) >> i)
self.assertEqual(res1, res3)
# ------------------------------ Slicing ------------------------------------
def adjust_step_positive(slicelength, start, stop, step):
"""
This is the adjust_step_positive() implementation from bitarray.h.
"""
if step < 0:
stop = start + 1
start = stop + step * (slicelength - 1) - 1
step = -step
assert start >= 0 and stop >= 0
assert step > 0
assert slicelength >= 0
if slicelength == 0:
assert stop <= start
elif step == 1:
assert stop - start == slicelength
return start, stop, step
def slicelength(start, stop, step):
"""
This is the slicelength implementation from PySlice_AdjustIndices().
a / b does integer division. If either a or b is negative, the result
depends on the compiler (rounding can go toward 0 or negative infinity).
Therefore, we are careful that both a and b are always positive.
"""
if step < 0:
if stop < start:
return (start - stop - 1) // (-step) + 1
else:
if start < stop:
return (stop - start - 1) // step + 1
return 0
class ListSliceTests(unittest.TestCase):
def random_slices(self, max_len=100, repeat=10_000):
for _ in range(repeat):
n = randint(0, max_len)
s = slice(randint(-n - 2, n + 2),
randint(-n - 2, n + 2),
randint(-5, 5) or 1)
yield n, s, range(n)[s]
def test_basic(self):
for n, s, r in self.random_slices():
self.assertEqual(range(*s.indices(n)), r)
def test_indices(self):
for n, s, r in self.random_slices():
start, stop, step = s.indices(n)
self.assertEqual(start, r.start)
self.assertEqual(stop, r.stop)
self.assertEqual(step, r.step)
self.assertNotEqual(step, 0)
if step > 0:
self.assertTrue(0 <= start <= n)
self.assertTrue(0 <= stop <= n)
else:
self.assertTrue(-1 <= start < n)
self.assertTrue(-1 <= stop < n)
self.assertEqual(range(start, stop, step), r)
def test_list_get(self):
for n, s, r in self.random_slices():
a = list(range(n))
b = a[s]
self.assertEqual(len(b), len(r))
self.assertEqual(b, list(r))
def test_list_set(self):
for n, s, r in self.random_slices(20):
a = n * [None]
b = list(a)
a[s] = range(len(r))
for i, j in enumerate(r):
b[j] = i
self.assertEqual(a, b)
def test_list_del(self):
for n, s, r in self.random_slices():
a = list(range(n))
b = list(a)
del a[s]
self.assertEqual(len(a), n - len(r))
for i in sorted(r, reverse=True):
del b[i]
self.assertEqual(a, b)
def test_adjust_step_positive(self):
for n, s, r in self.random_slices():
if s.step < 0:
r = r[::-1]
start, stop, step = adjust_step_positive(len(r), *s.indices(n))
self.assertEqual(range(start, stop, step), r)
self.assertTrue(step > 0)
if r:
self.assertTrue(0 <= start < n)
self.assertTrue(0 < stop <= n)
def test_slicelength(self):
for n, s, r in self.random_slices():
self.assertEqual(slicelength(r.start, r.stop, r.step), len(r))
# ------------------------- Modular Arithmetic ------------------------------
class ModularTests(unittest.TestCase):
def test_remainder(self):
for _ in range(1000):
a = randint(-20, 20)
b = randint(1, 20)
# integer division in Python returns the floor of the result
# instead of truncating towards zero like C
q = a // b
if a < 0:
self.assertTrue(q < 0)
r = a % b
self.assertEqual(b * q + r, a)
self.assertTrue(0 <= r < b)
def test_avoid_neg_numerator(self):
#
# equality: a % b = (b - (-a) % b) % b
#
for _ in range(1000):
a = randint(-20, 20)
b = randint(1, 20)
r = a % b
# Note that even though a may be negative, the remainder is
# always positive:
self.assertTrue(r >= 0)
# The following equality:
s = (b - (-a) % b) % b
self.assertEqual(s, r)
# can be used to implement a % b in C when a <= 0
if a <= 0:
# here % always operates on positive numerator
self.assertTrue(-a >= 0)
self.assertTrue(b - (-a) % b > 0)
# ----------------------------- Segments ------------------------------------
class SegmentTests(unittest.TestCase):
def test_nseg(self):
SEGSIZE = 32 # segment size in bytes
SEGBITS = 8 * SEGSIZE
for nbits in range(1000):
nbytes = (nbits + 7) // 8
# number of segments in terms of bytes
nseg = (nbytes + SEGSIZE - 1) // SEGSIZE
# and in terms of bits
self.assertEqual((nbits + SEGBITS - 1) // SEGBITS, nseg)
# number of complete segments
cseg = nbits // SEGBITS
self.assertTrue(cseg <= nseg)
# The number of complete segments cannot be calculated in terms
# of bytes, as it isn't possible to tell how many bits are
# actually used within the last byte of each segment.
if (nbits % SEGBITS > SEGBITS - 8):
self.assertNotEqual(nbytes // SEGSIZE, cseg)
else:
self.assertEqual(nbytes // SEGSIZE, cseg)
# remaining bits
rbits = nbits % SEGBITS
self.assertEqual(cseg * SEGBITS + rbits, nbits)
if cseg == nseg:
self.assertEqual(rbits, 0)
self.assertEqual(nbytes % SEGSIZE, 0)
else:
self.assertEqual(nseg, cseg + 1)
self.assertTrue(rbits > 0)
# ------------------------ Variable Length Format ---------------------------
class VLFTests(unittest.TestCase):
def test_padding(self):
LEN_PAD_BITS = 3
for nbits in range(1000):
n = (nbits + LEN_PAD_BITS + 6) // 7 # number of resulting bytes
padding = 7 * n - LEN_PAD_BITS - nbits
self.assertTrue(0 <= padding < 7)
self.assertEqual(divmod(nbits + padding + LEN_PAD_BITS, 7),
(n, 0))
# alternative equation for padding
padding_2 = (7 - (nbits + LEN_PAD_BITS) % 7) % 7
self.assertEqual(padding_2, padding)
if __name__ == '__main__':
unittest.main()
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