dec2hex.php

<?php
// Input: A decimal number as a String.
// Output: The equivalent hexadecimal number as a String.
function dec2hex($number) {
    $hexvalues = array('0','1','2','3','4','5','6','7', '8','9','A','B','C','D','E','F');
    $hexval = '';
    while($number != '0') {
        $hexval = $hexvalues[bcmod($number, '16')].$hexval;
        $number = bcdiv($number, '16', 0);
    }
    return $hexval;
}

// Input: A hexadecimal number as a String.
// Output: The equivalent decimal number as a String.
function hex2dec($number) {
    $decvalues = array(
        '0' => '0', '1' => '1', '2' => '2',
        '3' => '3', '4' => '4', '5' => '5',
        '6' => '6', '7' => '7', '8' => '8',
        '9' => '9', 'A' => '10', 'B' => '11',
        'C' => '12', 'D' => '13', 'E' => '14',
        'F' => '15'
    );
    $decval = '0';
    $number = strrev($number);
    for ($i = 0; $i < strlen($number); $i++) {
        $decval = bcadd(bcmul(bcpow('16', $i, 0), $decvalues[$number{$i}]), $decval);
    }
    return $decval;
}