问function_exists性能成本

EN

PHP 5.6.40 (1.000.000)
checkByFunction: 0.16808795928955
checkByVersion: 0.97429490089417

<?php
function checkByVersion($expectedMajor = 5, $expectedMinor = 5)
{
    //Explode (semver.org MAJOR.MINOR.PATCH)
    $phpversion = explode(".", phpversion());
    $phpversion_major = (int) $phpversion[0];
    $phpversion_minor = (int) $phpversion[1];

    //if php_version > 5 or 5.5
    if($phpversion_major > $expectedMajor || ($phpversion_major == $expectedMajor && $phpversion_minor >= $expectedMinor) ){
        return true;
    } else {
        return false;
    }
}

//Test
$iterations = 1000000;

$byFunctionTimeStart = 0;
$byFunctionTimeEnd = 0;

$byVersionTimeStart = 0;
$byVersionTimeEnd = 0;

//ByFunction
$byFunctionTimeStart = microtime(true);
for ($i=0; $i < $iterations; $i++) { 
    function_exists("curl_file_create");
}
$byFunctionTimeEnd = microtime(true);
$byFunctionTimeResult = $byFunctionTimeEnd - $byFunctionTimeStart;

//ByVersion
$byVersionTimeStart = microtime(true);
for ($i=0; $i < $iterations; $i++) { 
    checkByVersion();
}
$byVersionTimeEnd = microtime(true);
$byVersionTimeResult = $byVersionTimeEnd - $byVersionTimeStart;

echo "<pre>";
echo "PHP ".phpversion()." (".number_format($iterations, 0, ".", ".").")";
echo "<br/>checkByFunction: ".$byFunctionTimeResult;
echo "<br/>checkByVersion: ".$byVersionTimeResult;
echo "</pre>";