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The variant of editing distance we use doesn't satisfy the triangle inequality.

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gcc

	* spellcheck.c (test_data): Add problematic strings.
	(test_metric_conditions): Don't test the triangle inequality
	condition, which our distance function does not satisfy.
This commit is contained in:
Pip Cet 2020-07-01 14:58:52 -06:00 • committed by Jeff Law
parent be7c41a556
commit 34127f4ada
1 changed files with 8 additions and 14 deletions
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22
gcc/spellcheck.c
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@ -474,13 +474,17 @@ static const char * const test_data[] = {
"food",
"boo",
"1234567890123456789012345678901234567890123456789012345678901234567890"
"abc",
"ac",
"ca",
};
/* Verify that get_edit_distance appears to be a sane distance function,
i.e. the conditions for being a metric. This is done directly for a
small set of examples, using test_data above. This is O(N^3) in the size
of the array, due to the test for the triangle inequality, so we keep the
array small. */
even though it doesn't satisfy the conditions for being a metric. (This
is because the triangle inequality fails to hold: the distance between
"ca" and "ac" is 1, and so is the distance between "abc" and "ac", but
the distance between "abc" and "ca" is 3. Algorithms that calculate the
true Levenshtein-Damerau metric are much more expensive.) */
static void
test_metric_conditions ()
@ -504,16 +508,6 @@ test_metric_conditions ()
edit_distance_t dist_ji
= get_edit_distance (test_data[j], test_data[i]);
ASSERT_EQ (dist_ij, dist_ji);
/* Triangle inequality. */
for (int k = 0; k < num_test_cases; k++)
{
edit_distance_t dist_ik
= get_edit_distance (test_data[i], test_data[k]);
edit_distance_t dist_jk
= get_edit_distance (test_data[j], test_data[k]);
ASSERT_TRUE (dist_ik <= dist_ij + dist_jk);
}
}
}
}