PHP - Problem Comparing Dates

unix_timestamp values

start_date_time   1406411505 
end_date_time     1407275505
now               1406461573

SELECT i.item_id, 
		         i.title, 
		         i.price,
		         @start_date_time := CONVERT_TZ(i.start_date_time, '+00:00', u.time_zone),
		         @end_date_time := DATE_ADD(@start_date_time, INTERVAL 10 DAY),
		         @end_date_time AS `end_date_time`
		  FROM items i
		  LEFT JOIN sub_categories sc ON sc.sub_category_id = i.sub_category_id
		  LEFT JOIN categories c ON c.category_id = sc.category_id
		  JOIN users u ON username = 'Destramic'
		  WHERE UNIX_TIMESTAMP(@start_date_time) < UNIX_TIMESTAMP(NOW()) 
		  AND UNIX_TIMESTAMP(@end_date_time) >= UNIX_TIMESTAMP(NOW())

$a = array(1, 2, 3, 4, 5, 6);
$b = array(4, 6);
$y = '';
foreach ($a1 as $a){
 foreach ($b1 as $b){
  if ($a[val] == $b[val]){
  $y = '*';
  }
}
echo $y.$a.'<br />';
}  

When a file is uploaded, I wish to determine whether an existing identical file (regardless of what it is named or what extension it has) already exists and if so don't save the newly uploaded file but just point it to the existing one.  My primary reason for doing so is not really to save hard drive space but to be able to manage duplicate documents.

One option is to store a hash of the documents in the DB and when a new document is uploaded, query the DB to see if an identical hash exists.  How certain can one be that two hashes will never be duplicated?

Another option is to compare the byte stream.  For this, I would first query the DB to see if a file with same size and media type exists, and then compare the document to all existing files which have that same criteria.

Or many some other approach?

Recommendations?

Thanks

<?php

error_reporting(E_ALL);
ini_set('display_startup_errors', 1);
ini_set('display_errors', 1);

function compareFilesTest(string $file_a, string $file_b)
{
    $time = microtime(true);
    display($time, $file_a, $file_b, 'compareFilesTest', compareFiles($file_a, $file_b));
}
function compareFilesTest2(string $file_a, string $file_b)
{
    $time = microtime(true);
    display($time, $file_a, $file_b, 'compareFilesTest2', identical($file_a, $file_b));
}

function compareFilesHashTest(string $file_a, string $file_b, string $algo = 'md5')
{
    $time = microtime(true);
    display($time, $file_a, $file_b, 'compareFilesHashTest', hash_file($algo, $file_a)===hash_file($algo, $file_b), $algo);
}

function display(float $time, string $file_a, string $file_b, string $test, bool $status, string $algorithm=null)
{
    printf("\n%s\nFile1: %s\nFile2: %s\nStatus: %s\nTime (uS): %d\n", $test.($algorithm?" ($algorithm)":''), $file_a, $file_b, $status?'EQUAL':'NOT EQUAL', 1000000*(microtime(true) - $time));
}

function compareFiles(string $file_a, string $file_b):bool
{
    if (filesize($file_a) == filesize($file_b))
    {
        $fp_a = fopen($file_a, 'rb');
        $fp_b = fopen($file_b, 'rb');

        while (!feof($fp_a) && ($b = fread($fp_a, 4096)) !== false) {
            $b_b = fread($fp_b, 4096);
            if ($b !== $b_b)
            {
                fclose($fp_a);
                fclose($fp_b);
                return false;
            }
        }

        fclose($fp_a);
        fclose($fp_b);

        return true;
    }

    return false;
}

function identical($fileOne, $fileTwo)
{
    if (filetype($fileOne) !== filetype($fileTwo)) return false;
    if (filesize($fileOne) !== filesize($fileTwo)) return false;

    if (! $fp1 = fopen($fileOne, 'rb')) return false;

    if (! $fp2 = fopen($fileTwo, 'rb'))
    {
        fclose($fp1);
        return false;
    }

    $same = true;

    while (! feof($fp1) and ! feof($fp2))
        if (fread($fp1, 4096) !== fread($fp2, 4096))
        {
            $same = false;
            break;
        }

        if (feof($fp1) !== feof($fp2)) $same = false;

    fclose($fp1);
    fclose($fp2);

    return $same;
}

$path = __DIR__.'/test_documents/';

//print_r(hash_algos());

compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpg');
compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c1c96440_MasterFormat-2016.pdf');
compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'x602a9c07af00c_IMG_1225.jpg');
compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpgx');
compareFilesHashTest($path.'file1.txt', $path.'file2.md');
compareFilesHashTest($path.'file1.txt', $path.'file3.txt');

compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpg', 'sha256');
compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c1c96440_MasterFormat-2016.pdf', 'sha256');
compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'x602a9c07af00c_IMG_1225.jpg', 'sha256');
compareFilesHashTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpgx', 'sha256');
compareFilesHashTest($path.'file1.txt', $path.'file2.md', 'sha256');
compareFilesHashTest($path.'file1.txt', $path.'file3.txt', 'sha256');

compareFilesTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpg');
compareFilesTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c1c96440_MasterFormat-2016.pdf');
compareFilesTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'x602a9c07af00c_IMG_1225.jpg');
compareFilesTest($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpgx');
compareFilesTest($path.'file1.txt', $path.'file2.md');
compareFilesTest($path.'file1.txt', $path.'file3.txt');

compareFilesTest2($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpg');
compareFilesTest2($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c1c96440_MasterFormat-2016.pdf');
compareFilesTest2($path.'602a9c07af00c_IMG_1225.jpg', $path.'x602a9c07af00c_IMG_1225.jpg');
compareFilesTest2($path.'602a9c07af00c_IMG_1225.jpg', $path.'602a9c07af00c_IMG_1225.jpgx');
compareFilesTest2($path.'file1.txt', $path.'file2.md');
compareFilesTest2($path.'file1.txt', $path.'file3.txt');