Various StartsWith implementations

startswith_benchmark.php

<?php

/*
Run with all available processing power:

sudo nice -n -20 php startswith_benchmark.php | sort -h

Running with PHP 7.0.7-3 gives:

1.6±0.0014 msec - strncmp_startswith_shortcut
1.71±0.0014 msec - strncmp_startswith
1.78±0.0013 msec - substr_compare_startswith
1.84±0.0013 msec - substr_startswith
2.89±0.0025 msec - strpos_startswith
78.86±0.1781 msec - preg_match_startswith

*/


function substr_startswith($haystack, $needle) {
    return substr($haystack, 0, strlen($needle)) === $needle;
}

function preg_match_startswith($haystack, $needle) {
    return preg_match('~'.preg_quote($needle,'~').'~A', $haystack) > 0;
}

function substr_compare_startswith($haystack, $needle) {
    return substr_compare($haystack, $needle, 0, strlen($needle)) === 0;
}

function strpos_startswith($haystack, $needle) {
    return strpos($haystack, $needle) === 0;
}

function strncmp_startswith($haystack, $needle) {
    return strncmp($haystack, $needle, strlen($needle)) === 0;
}

function strncmp_startswith_shortcut($haystack, $needle) {
    return $haystack[0] === $needle[0]
        ? strncmp($haystack, $needle, strlen($needle)) === 0
        : false;
}

// helper functions
function randstr($len) {
    return substr(base64_encode(openssl_random_pseudo_bytes(ceil($len * 3 / 4))), 0, $len);
}

function avg_value($values) {
    return array_sum($values) / sizeof($values);
}

function stddev_value($values) {
    $mean = array_sum($values) / sizeof($values);
    return (float) sqrt(array_reduce($values, function ($variance, $delay) use ($mean) {
        return $variance + pow($delay - $mean, 2);
    }, 0) / (sizeof($values)));
}


echo 'generating tests';
for ($i = 0; $i < 100000; $i += 1) {
    if ($i % 1000 === 0) echo '.';
    // 99,9% of random cases are failing
    $test_cases[] = $randomCase = [
        'haystack' => randstr(mt_rand(1, 7000)),
        'needle' => randstr(mt_rand(1, 3000)),
    ];

    // in real life not every call fails
    // therefore we need to benchmark succeding calls too
    $randomCase['haystack'] = $randomCase['needle'].$randomCase['needle'];
    $test_cases[] = $randomCase;
}
echo "done!\n";

foreach ([
    'substr_startswith',
    'preg_match_startswith',
    'substr_compare_startswith',
    'strpos_startswith',
    'strncmp_startswith',
    'strncmp_startswith_shortcut',
] as $func) {
    $times = [];

    foreach($test_cases as $tc) {
        $start = microtime(true);
        $func($tc['haystack'], $tc['needle']);
        $times[] = microtime(true) - $start;
    }

    // seconds to msec
    $times = array_map(function ($seconds) {
        return $seconds * 1000 * 1000;
    }, $times);

    $elapsed = round(array_sum($times), 4);
    $avg = round(avg_value($times), 2);
    $stddev = round(stddev_value($times), 2);
    $stderr = round($stddev / sqrt(sizeof($times)), 4);
    echo "{$avg}±{$stderr} msec - $func\n"; //  (sigma $stddev total $elapsed)
}