There is a floor in this (pun intended), even chatGPT can't explain it

[perlsol]

function abbreviateNumber($number) {
if ($number >= 1000000000) {
$abbreviated = number_format($number / 1000000000, 1) . 'B';
} elseif ($number >= 1000000) {
$abbreviated = number_format($number / 1000000, 1) . 'M';
} elseif ($number >= 1000) {
$abbreviated = number_format($number / 1000, 0) . 'K';
} else {
$abbreviated = $number;
}
return $abbreviated;
}

function countLines($filename) {
$lineCount = 0;

$file = new SplFileObject($filename);
$file->setFlags(SplFileObject::READ_AHEAD | SplFileObject::SKIP_EMPTY);

foreach ($file as $line) {
    if ($line !== false) {
        $lineCount++;
    }
}

return $lineCount;

}

$filename = 'archive.tmp';
$lines = countLines($filename);
$roundedDown = floor($lines / 1000) * 1000;
$abbreviatedNumber = abbreviateNumber($roundedDown);

echo $abbreviatedNumber . "+ IP's LISTED";

archive.tmp contains 1056241 ip addresses, why does abbreviatedNumber say 1.1M when it should say 1.0M
My guess is it is not rounding down, it said 1.0 when it was just over 1M IP addresses in the file

[TimWolla]

My guess is it is not rounding down,

You're rounding to the nearest 1000, not to the nearest million. In any case this is neither a documentation issue, nor a bug in PHP. Please use some forum, such as StackOverflow, if you need programming help.