8000 BUG: Don't produce undefined behavior for a << b if b >= bitsof(a) by eric-wieser · Pull Request #13739 · numpy/numpy · GitHub
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BUG: Don't produce undefined behavior for a << b if b >= bitsof(a) #13739

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Merged
merged 7 commits into from
Sep 14, 2019
Merged

BUG: Don't produce undefined behavior for a << b if b >= bitsof(a) #13739

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24b2a2d
BUG: shift operator cycles, fixes #2449
jaimefrio Mar 27, 2016
b12a869
Merge tag 'branch-points/1.16.x' into bit_shifts
eric-wieser Jun 8, 2019
e487889
Merge tag 'branch-points/1.17.x' into HEAD
eric-wieser Sep 13, 2019
ff11d01
Merge commit 'edf8a5f' into HEAD
eric-wieser Sep 13, 2019
fca077c
MAINT: Respond to review comments on gh-7473
eric-wieser Jun 9, 2019
79d7bc2
MAINT: Move shift implementation to npy_math
eric-wieser Jun 12, 2019
6cf6ece
BUG: Disable -O3 on right_shift on compilers which emit an internal e…
eric-wieser Jun 12, 2019
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MAINT: Respond to review comments on gh-7473 
This:
* Inlines the macros in loops.c.src
* Replaces 8 with `CHAR_BIT `. The `NPY_SIZEOF_*` macros are not used here because it's too much work to apply them to the signed types, and they expand to the same thing anyway.
* Removes the reduce loop specializations which likely no one cares about
* Uses pytest.mark.parametrize to shorten the test
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@eric-wieser
eric-wieser committed Sep 13, 2019
commit fca077c7e2fc8f21c639ba479267a34eb16a2810
104 changes: 27 additions & 77 deletions numpy/core/src/umath/loops.c.src
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Expand Up @@ -777,7 +777,7 @@ NPY_NO_EXPORT NPY_GCC_OPT_3 @ATTR@ void
/**begin repeat2
* Arithmetic
* #kind = add, subtract, multiply, bitwise_and, bitwise_or, bitwise_xor#
* #OP = +, -,*, &, |, ^#
* #OP = +, -, *, &, |, ^#
*/

#if @CHK@
Expand Down Expand Up @@ -808,98 +808,48 @@ NPY_NO_EXPORT NPY_GCC_OPT_3 @ATTR@ void
* which is undefined in C.
*/

#define LEFT_SHIFT_OP \
do { \
if (NPY_LIKELY(in2 < sizeof(@type@) * 8)) { \
*out = in1 << in2; \
} \
else { \
*out = 0; \
} \
} while (0)


NPY_NO_EXPORT NPY_GCC_OPT_3 void
@TYPE@_left_shift@isa@(char **args, npy_intp *dimensions, npy_intp *steps,
void *NPY_UNUSED(func))
{
if (IS_BINARY_REDUCE) {
BINARY_REDUCE_LOOP(@type@) {
@type@ ip2_val = *(@type@ *)ip2;

if (NPY_LIKELY(ip2_val < sizeof(@type@) * 8)) {
io1 <<= ip2_val;
}
else {
io1 = 0;
}
BINARY_LOOP_FAST(@type@, @type@,
if (NPY_LIKELY(in2 < sizeof(@type@) * CHAR_BIT)) {
*out = in1 << in2;
}
*((@type@ *)iop1) = io1;
}
else {
BINARY_LOOP_FAST(@type@, @type@, LEFT_SHIFT_OP);
}
}

#undef LEFT_SHIFT_OP

#define RIGHT_SHIFT_OP_SIGNED \
do { \
if (NPY_LIKELY(in2 < sizeof(@type@) * 8)) { \
*out = in1 >> in2; \
} \
else if (in1 < 0) { \
*out = -1; \
} \
else { \
*out = 0; \
} \
} while (0)

#define RIGHT_SHIFT_OP_UNSIGNED \
do { \
if (NPY_LIKELY(in2 < sizeof(@type@) * 8)) { \
*out = in1 >> in2; \
} \
else { \
*out = 0; \
} \
} while (0)
else {
*out = 0;
}
);
}

NPY_NO_EXPORT NPY_GCC_OPT_3 void
@TYPE@_right_shift@isa@(char **args, npy_intp *dimensions, npy_intp *steps,
void *NPY_UNUSED(func))
{
if (IS_BINARY_REDUCE) {
BINARY_REDUCE_LOOP(@type@) {
@type@ ip2_val = *(@type@ *)ip2;

if (NPY_LIKELY(ip2_val < sizeof(@type@) * 8)) {
io1 >>= ip2_val;
}
#if @SIGNED@
else if (io1 < 0) {
io1 = -1;
}
#endif
else {
io1 = 0;
}
BINARY_LOOP_FAST(@type@, @type@, {
if (NPY_LIKELY(in2 < sizeof(@type@) * CHAR_BIT)) {
*out = in1 >> in2;
}
*((@type@ *)iop1) = io1;
}
else {
#if @SIGNED@
BINARY_LOOP_FAST(@type@, @type@, RIGHT_SHIFT_OP_SIGNED);
else if (in1 < 0) {
*out = (@type@)-1; /* shift right preserves the sign bit */
}
else {
*out = 0;
}
});
#else
BINARY_LOOP_FAST(@type@, @type@, RIGHT_SHIFT_OP_UNSIGNED);
BINARY_LOOP_FAST(@type@, @type@, {
if (NPY_LIKELY(in2 < sizeof(@type@) * CHAR_BIT)) {
*out = in1 >> in2;
}
else {
*out = 0;
}
});
#endif
}
}

#undef RIGHT_SHIFT_OP_SIGNED
#undef RIGHT_SHIFT_OP_UNSIGNED


/**begin repeat2
* #kind = equal, not_equal, greater, greater_equal, less, less_equal,
Expand Down
56 changes: 29 additions & 27 deletions numpy/core/src/umath/scalarmath.c.src
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Expand Up @@ -263,38 +263,40 @@ static void

/**end repeat1**/

#define @name@_ctype_lshift(arg1, arg2, out) \
do { \
if (NPY_LIKELY((arg2) < sizeof(@type@) * 8)) { \
*(out) = (arg1) << (arg2); \
} \
else { \
*(out) = 0; \
} \
/* Note: these need to be kept in sync with the shift ufuncs */

#define @name@_ctype_lshift(arg1, arg2, out) \
do { \
if (NPY_LIKELY((arg2) < sizeof(@type@) * CHAR_BIT)) { \
*(out) = (arg1) << (arg2); \
} \
else { \
*(out) = 0; \
} \
} while (0)

#if @issigned@
#define @name@_ctype_rshift(arg1, arg2, out) \
do { \
if (NPY_LIKELY((arg2) < sizeof(@type@) * 8)) { \
*(out) = (arg1) >> (arg2); \
} \
else if ((arg1) < 0) { \
*(out) = -1; \
} \
else { \
*(out) = 0; \
} \
#define @name@_ctype_rshift(arg1, arg2, out) \
do { \
if (NPY_LIKELY((arg2) < sizeof(@type@) * CHAR_BIT)) { \
*(out) = (arg1) >> (arg2); \
} \
else if ((arg1) < 0) { \
*(out) = -1; \
} \
else { \
*(out) = 0; \
} \
} while (0)
#else
#define @name@_ctype_rshift(arg1, arg2, out) \
do { \
if (NPY_LIKELY((arg2) < sizeof(@type@) * 8)) { \
*(out) = (arg1) >> (arg2); \
} \
else { \
*(out) = 0; \
} \
#define @name@_ctype_rshift(arg1, arg2, out) \
do { \
if (NPY_LIKELY((arg2) < sizeof(@type@) * CHAR_BIT)) { \
*(out) = (arg1) >> (arg2); \
} \
else { \
*(out) = 0; \
} \
} while (0)
#endif

Expand Down
46 changes: 21 additions & 25 deletions numpy/core/tests/test_scalarmath.py
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Expand Up @@ -668,31 +668,27 @@ def test_numpy_abs(self):

class TestBitShifts(object):

def test_left_shift(self):
@pytest.mark.parametrize('type_code', np.typecodes['AllInteger'])
@pytest.mark.parametrize('op',
[operator.rshift, operator.lshift], ids=['>>', '<<'])
def test_shift_all_bits(self, type_code, op):
""" Shifts where the shift amount is the width of the type or wider """
# gh-2449
for dt in np.typecodes['AllInteger']:
arr = np.array([5, -5], dtype=dt)
scl_pos, scl_neg = arr
for shift in np.array([arr.dtype.itemsize * 8], dtype=dt):
res_pos = scl_pos << shift
res_neg = scl_neg << shift
assert_equal(res_pos, 0)
assert_equal(res_neg, 0)
# Result on scalars should be the same as on arrays
assert_array_equal(arr << shift, [res_pos, res_neg])

def test_right_shift(self):
# gh-2449
for dt in np.typecodes['AllInteger']:
arr = np.array([5, -5], dtype=dt)
scl_pos, scl_neg = arr
for shift in np.array([arr.dtype.itemsize * 8], dtype=dt):
res_pos = scl_pos >> shift
res_neg = scl_neg >> shift
assert_equal(res_pos, 0)
if dt in np.typecodes['UnsignedInteger']:
assert_equal(res_neg, 0)
dt = np.dtype(type_code)
nbits = dt.itemsize * 8
for val in [5, -5]:
for shift in [nbits, nbits + 4]:
val_scl = dt.type(val)
shift_scl = dt.type(shift)
res_scl = op(val_scl, shift_scl)
if val_scl < 0 and op is operator.rshift:
# sign bit is preserved
assert_equal(res_scl, -1)
else:
assert_equal(res_neg, -1)
assert_equal(res_scl, 0)

# Result on scalars should be the same as on arrays
assert_array_equal(arr >> shift, [res_pos, res_neg], dt)
val_arr = np.array([val]*32, dtype=dt)
shift_arr = np.array([shift]*32, dtype=dt)
res_arr = op(val_arr, shift_arr)
assert_equal(res_arr, res_scl)
0