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Use smaller epsilon and relative error for float comparison #1570

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merged 3 commits into from Sep 11, 2021
Merged

Use smaller epsilon and relative error for float comparison #1570

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7563926
Use smaller epsilon and relative error for float comparison
sanmai Sep 11, 2021
5244bf7
Use common epsilon here and there
sanmai Sep 11, 2021
62811fb
Document the constant
sanmai Sep 11, 2021
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25 changes: 24 additions & 1 deletion tests/phpunit/TestFramework/Coverage/JUnit/TestLocationBucketSorterTest.php
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Expand Up @@ -59,6 +59,13 @@
*/
final class TestLocationBucketSorterTest extends TestCase
{
/**
* Used for floating point comparisons.
*
* @var float
*/
private const EPSILON = 0.001;

public function test_it_sorts(): void
{
$testLocation = new TestLocation('', '', 0.0);
Expand Down Expand Up @@ -189,7 +196,7 @@ public function test_it_sorts_faster_than_quicksort(ArrayIterator $uniqueTestLoc
$totalQuickSort += microtime(true) - $start;
}

$this->assertGreaterThanOrEqual(0.01, abs($totalQuickSort - $totalBucketSort));
$this->assertGreaterThanOrEqual(self::EPSILON, self::getRelativeError($totalQuickSort, $totalBucketSort));
}

public static function locationsArrayProvider(): iterable
Expand All @@ -206,6 +213,22 @@ static function (float $executionTime): TestLocation {
yield 'All locations' => [new ArrayIterator($locations)];
}

/**
* Finds relative error.
*
* @see https://floating-point-gui.de/errors/comparison/
* @see https://stackoverflow.com/questions/4915462/how-should-i-do-floating-point-comparison
*/
private static function getRelativeError(float $a, float $b): float
{
// We do not expect A or B to be extremely small or large: these are edge cases,
// and they will need special handling which we avoid simplicity sake.
self::assertGreaterThan(self::EPSILON, abs($a));
self::assertGreaterThan(self::EPSILON, abs($b));

return abs($a - $b) / (abs($a) + abs($b));
}

private static function quicksort(&$uniqueTestLocations): void
{
usort(
Expand Down