phpexcel_tools.php

<?php
    /**
     * Converts a column name into the corresponding index (A = 0, B = 1, AA = 26, etc).
     * 
     * @param string $name
     * @return int
     */
    function getColumnIndexFromName($name)
    {
        $chars = array_map(function($char) { return ord($char); }, str_split(strtoupper($name)));
        $index = 0;
        $pow = 1;
        
        for($i = count($chars) - 1; $i >= 0; $i--)
        {
            $index += (($chars[$i] - ord('A') + 1) * $pow);
            $pow *= 26;
        }
        
        return $index - 1;
    }
    
    /**
     * Converts a column index to the corresponding name (0 = A, 1 = B, 26 = AA, etc).
     * 
     * @param int $index
     * @return string
     * @throws OutOfRangeException
     */
    function getColumnNameFromIndex($index)
    {
        if($index < 0)
            throw new OutOfRangeException();
        
        $chars = array();
        
        while($index >= 0)
        {
            $chars[] = chr(ord('A') + ($index % 26));
            $index = intdiv($index, 26) - 1;
        }

        return implode('', array_reverse($chars));
    }