Result
Unfortunately, no history for this test is available.
Code
The first test, "substr()", was:
for ($j = 0; $j < 100; $j++) $GLOBALS['dummy2'] = substr($GLOBALS['dummy'], 25, 1);
The second test, "isset {5}", was:
for ($j = 0; $j < 100; $j++) $GLOBALS['dummy2'] = isset($GLOBALS['dummy']{25}) ? $GLOBALS['dummy']{25} : '';