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garray: Fix binary search for non-existent elements on the left

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If searching for an element which is smaller than every element in the
array (i.e. the element being searched for is not in the array), the
previous g_array_binary_search() implementation would underflow in the
calculation `right = middle - 1`, and end up trying to dereference an
element way off the right of the array.

Fix that by checking the additions/subtractions before doing them, and
bailing if the bounds are hit. We don’t need to check `middle <
G_MAXUINT`, as `middle` is bounded above by `right`, which is always `<=
_array->len - 1`, and `_array->len <= G_MAXUINT`.

Add some tests for that, and for not-present elements in the middle of
the array. Previously, the tests only checked for not-present elements
which were bigger than every element in the array.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
This commit is contained in:
Philip Withnall 2019-07-16 11:36:28 +01:00
parent ec61daf503
commit c0f13f3cc8
2 changed files with 47 additions and 16 deletions
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12
glib/garray.c
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@ -848,15 +848,17 @@ g_array_binary_search (GArray *array,
middle = left + (right - left) / 2;
val = compare_func (_array->data + (_array->elt_size * middle), target);
if (val < 0)
left = middle + 1;
else if (val > 0)
right = middle - 1;
else
if (val == 0)
{
result = TRUE;
break;
}
else if (val < 0)
left = middle + 1;
else if (/* val > 0 && */ middle > 0)
right = middle - 1;
else
break; /* element not found */
}
}

51
glib/tests/array-test.c
View File

@ -677,6 +677,9 @@ test_array_binary_search (void)
g_assert_true (g_array_binary_search (garray, &i, cmpint, NULL));
i = 0;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
i = 2;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
@ -684,26 +687,32 @@ test_array_binary_search (void)
/* Testing array of size 2 */
garray = g_array_sized_new (FALSE, FALSE, sizeof (guint), 2);
for (i = 0; i < 2; i++)
for (i = 1; i < 3; i++)
g_array_append_val (garray, i);
for (i = 0; i < 2; i++)
for (i = 1; i < 3; i++)
g_assert_true (g_array_binary_search (garray, &i, cmpint, NULL));
i = 3;
i = 0;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
i = 4;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
g_array_free (garray, TRUE);
/* Testing array of size 3 */
garray = g_array_sized_new (FALSE, FALSE, sizeof (guint), 3);
for (i = 0; i < 3; i++)
for (i = 1; i < 4; i++)
g_array_append_val (garray, i);
for (i = 0; i < 3; i++)
for (i = 1; i < 4; i++)
g_assert_true (g_array_binary_search (garray, &i, cmpint, NULL));
i = 4;
i = 0;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
i = 5;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
g_array_free (garray, TRUE);
@ -711,23 +720,43 @@ test_array_binary_search (void)
/* Testing array of size 10000 */
garray = g_array_sized_new (FALSE, FALSE, sizeof (guint), 10000);
for (i = 0; i < 10000; i++)
for (i = 1; i < 10001; i++)
g_array_append_val (garray, i);
for (i = 0; i < 10000; i++)
for (i = 1; i < 10001; i++)
g_assert_true (g_array_binary_search (garray, &i, cmpint, NULL));
for (i = 0; i < 10000; i++)
for (i = 1; i < 10001; i++)
{
g_assert_true (g_array_binary_search (garray, &i, cmpint, &matched_index));
g_assert_cmpint (i, ==, matched_index);
g_assert_cmpint (i, ==, matched_index + 1);
}
/* Testing negative result */
i = 10001;
i = 0;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
g_assert_false (g_array_binary_search (garray, &i, cmpint, &matched_index));
i = 10002;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
g_assert_false (g_array_binary_search (garray, &i, cmpint, &matched_index));
g_array_free (garray, TRUE);
/* Test for a not-found element in the middle of the array. */
garray = g_array_sized_new (FALSE, FALSE, sizeof (guint), 3);
for (i = 1; i < 10; i += 2)
g_array_append_val (garray, i);
i = 0;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
i = 2;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
i = 10;
g_assert_false (g_array_binary_search (garray, &i, cmpint, NULL));
g_array_free (garray, TRUE);
}