Bcmath adding decimal places randomly - php

Question

I have a PHP function I got from the web that uses bcmath functions:
function SteamID64to32($steamId64) {
$iServer = "1";
if(bcmod($steamId64, "2") == "0") {
$iServer = "0";
}
$steamId64 = bcsub($steamId64,$iServer);
if(bccomp("76561197960265728",$steamId64) == -1) {
$steamId64 = bcsub($steamId64,"76561197960265728");
}
$steamId64 = bcdiv($steamId64, "2");
return ("STEAM_0:" . $iServer . ":" . $steamId64);
}
For any valid input the function will at random times add ".0000000000" to the output.
Ex:
$input = 76561198014791430;
SteamID64to32($input);
//result for each run
STEAM_0:0:27262851
STEAM_0:0:27262851.0000000000
STEAM_0:0:27262851
STEAM_0:0:27262851
STEAM_0:0:27262851.0000000000
STEAM_0:0:27262851
STEAM_0:0:27262851.0000000000
STEAM_0:0:27262851.0000000000
STEAM_0:0:27262851.0000000000
This was tested on 2 different nginx servers running php-fpm.
Please help me understand what is wrong here. Thanks

Answer 1

The answer provided by JD doesn't account for all possible STEAM_ ID types, namely, anything that is in the STEAM_0:1 range. This block of code will:
<?php
function Steam64ToSteam32($Steam64ID)
{
$offset = $Steam64ID - 76561197960265728;
$id = ($offset / 2);
if($offset % 2 != 0)
{
$Steam32ID = 'STEAM_0:1:' . bcsub($id, '0.5');
}
else
{
$Steam32ID = "STEAM_0:0:" . $id;
}
return $Steam32ID;
}
echo Steam64ToSteam32(76561197960435530);
echo "<br/>";
echo Steam64ToSteam32(76561197990323733);
echo "<br/>";
echo Steam64ToSteam32(76561198014791430);
?>
This outputs
STEAM_0:0:84901
STEAM_0:1:15029002
STEAM_0:0:27262851
The first one is for a Valve employee and someone who's had a Steam account since 2003 (hence the low ID), the second is a random profile I found on VACBanned which had an ID in the STEAM_0:1 range. The third is the ID you provided in your sample code.

Answer 2

I found this: SteamProfile
/**
* This file is part of SteamProfile.
*
* Written by Nico Bergemann <barracuda415#yahoo.de>
* Copyright 2009 Nico Bergemann
*
* SteamProfile is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* SteamProfile is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with SteamProfile. If not, see <http://www.gnu.org/licenses/>.
*/
// thanks to voogru for the id transformation algorithm (http://forums.alliedmods.net/showthread.php?t=60899)
class SteamID {
private $sSteamID = '';
private $sSteamComID = '';
const STEAMID64_BASE = '76561197960265728';
public function __construct($sID) {
// make sure the bcmath extension is loaded
if(!extension_loaded('bcmath')) {
throw new RuntimeException("BCMath extension required");
}
if($this->isValidSteamID($sID)) {
$this->sSteamID = $sID;
$this->sSteamComID = $this->convertToSteamComID($sID);
} elseif($this->isValidComID($sID)) {
$this->sSteamID = $this->convertToSteamID($sID);
$this->sSteamComID = $sID;
} else {
$this->sSteamID = '';
$this->sSteamComID = '';
}
}
public function getSteamID() {
return $this->sSteamID;
}
public function getSteamComID() {
return $this->sSteamComID;
}
public function isValid() {
return $this->sSteamID != '';
}
private function isValidSteamID($sSteamID) {
return preg_match('/^(STEAM_)?[0-5]:[0-9]:\d+$/i', $sSteamID);
}
private function isValidComID($sSteamComID) {
// anything else than a number is invalid
// (is_numeric() doesn't work for 64 bit integers)
if(!preg_match('/^\d+$/i', $sSteamComID)) {
return false;
}
// the community id must be bigger than STEAMID64_BASE
if(bccomp(self::STEAMID64_BASE, $sSteamComID) == 1) {
return false;
}
// TODO: Upper limit?
return true;
}
private function convertToSteamComID($sSteamID) {
$aTMP = explode(':', $sSteamID);
$sServer = $aTMP[1];
$sAuth = $aTMP[2];
if((count($aTMP) == 3) && $sAuth != '0' && is_numeric($sServer) && is_numeric($sAuth)) {
$sComID = bcmul($sAuth, "2"); // multipy Auth-ID with 2
$sComID = bcadd($sComID, $sServer); // add Server-ID
$sComID = bcadd($sComID, self::STEAMID64_BASE); // add this odd long number
// It seems that PHP appends ".0000000000" at the end sometimes.
// I can't find a reason for this, so I'll take the dirty way...
$sComID = str_replace('.0000000000', '', $sComID);
return $sComID;
} else {
throw new RuntimeException("Unable to convert Steam-ID");
}
}
private function convertToSteamID($sSteamComID) {
$sServer = bcmod($sSteamComID, '2') == '0' ? '0' : '1';
$sCommID = bcsub($sSteamComID, $sServer);
$sCommID = bcsub($sCommID, self::STEAMID64_BASE);
$sAuth = bcdiv($sCommID, '2');
return "STEAM_0:$sServer:$sAuth";
}
}