Adding 2 hexadecimals as strings - php

Question

Description
I'm trying to get the data for a decall image for a Team Fortress 2 item from steam
http://forums.steampowered.com/forums/showthread.php?t=2695676
Data used
steam inventory item attributes
"attributes": [
{
"defindex": 152,
"value": 160020469,
"float_value": 3.3154542658454145e-033
},
{
"defindex": 227,
"value": 142668139,
"float_value": 7.7604768692394667e-034
},
{
"defindex": 746,
"value": 1065353216,
"float_value": 1
},
{
"defindex": 292,
"value": 1115684864,
"float_value": 64
},
{
"defindex": 388,
"value": 1115684864,
"float_value": 64
}
]
My script
`
function Function_BigDecimal_to_Hexadecimal_Converter($dec) {
$hex = '';
do {
$last = bcmod($dec, 16);
$hex = dechex($last).$hex;
$dec = bcdiv(bcsub($dec, $last), 16);
} while($dec>0);
return $hex;
}
function Function_BigHexadecimal_to_Decimal_Converter($hex) {
$dec = 0; $len = strlen($hex);
for ($i = 1; $i <= $len; $i++) { $dec = bcadd($dec, bcmul(strval(hexdec($hex[$i - 1])), bcpow('16', strval($len - $i)))); }
return $dec;
}
$hex1 = Function_BigDecimal_to_Hexadecimal_Converter('142668139' ); // data from defindex 227
$hex2 = Function_BigDecimal_to_Hexadecimal_Converter('160020469'); // data from defindex 152
echo 'hex1 ',$hex1,'<br>'; // = 880f16b
echo 'hex2 ',$hex2,'<br>'; // = 989b7f5
$hex_append = $hex1.$hex2;
echo 'hex_append ',$hex_append,'<br>'; // = 880f16b989b7f5
$ugcid = Function_BigHexadecimal_to_Decimal_Converter($hex_append);
echo 'ugcid ',$ugcid,'<br>'; // = 38297187109156853
`
My problem
expected ucid value shoud be 612754991346202613 and I got 38297187109156853
Here i'm reversing this code to get hex_append from the expected answer
echo 'Reversed hex_append using expected answer '.Function_BigDecimal_to_Hexadecimal_Converter('612754991346202613');// = 880f16b0989b7f5
Conclusion
The difference in hex_append calculated 880f16b989b7f5 and the reversed answer 880f16b0989b7f5 is a 0
How can I fix this ?
I guess the a 0 needs to be added sometimes when adding 2 hexes as strings.
This problem was detected only for this item.
All this php code con be copyed in a php file and executed

Answer 1

Answer: The string must have 18 characters