Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Statistical.php
public static function PERCENTILE(...$args)
    {
        $aArgs = Functions::flattenArray($args);

        // Calculate
        $entry = array_pop($aArgs);

        if ((is_numeric($entry)) && (!is_string($entry))) {
            if (($entry < 0) || ($entry > 1)) {
                return Functions::NAN();
            }
            $mArgs = [];
            foreach ($aArgs as $arg) {
                // Is it a numeric value?
                if ((is_numeric($arg)) && (!is_string($arg))) {
                    $mArgs[] = $arg;
                }
            }
            $mValueCount = count($mArgs);
            if ($mValueCount > 0) {
                sort($mArgs);
                $count = self::COUNT($mArgs);
                $index = $entry * ($count - 1);
                $iBase = floor($index);
                if ($index == $iBase) {
                    return $mArgs[$index];
                }
                $iNext = $iBase + 1;
                $iProportion = $index - $iBase;

                return $mArgs[$iBase] + (($mArgs[$iNext] - $mArgs[$iBase]) * $iProportion);
            }
        }

        return Functions::VALUE();
    }
public static function PERCENTILE(...$args)
    {
        $aArgs = Functions::flattenArray($args);

        // Calculate
        $entry = array_pop($aArgs);

        if ((is_numeric($entry)) && (!is_string($entry))) {
            if (($entry < 0) || ($entry > 1)) {
                return Functions::NAN();
            }
            $mArgs = [];
            foreach ($aArgs as $arg) {
                // Is it a numeric value?
                if ((is_numeric($arg)) && (!is_string($arg))) {
                    $mArgs[] = $arg;
                }
            }
            $mValueCount = count($mArgs);
            if ($mValueCount > 0) {
                sort($mArgs);
                $count = self::COUNT($mArgs);
                $index = $entry * ($count - 1);
                $iBase = floor($index);
                if ($index == $iBase) {
                    return $mArgs[$index];
                }
                $iNext = $iBase + 1;
                $iProportion = $index - $iBase;

                return $mArgs[$iBase] + (($mArgs[$iNext] - $mArgs[$iBase]) * $iProportion);
            }
        }

        return Functions::VALUE();
    }
PERCENTILE.

Returns the nth percentile of values in a range..

Excel Function:
PERCENTILE(value1[,value2[, ...]],entry)

@category Statistical Functions

@param mixed $args Data values
@param float $entry Percentile value in the range 0..1, inclusive.

@return float