How to compare large number in PHP?

I confuse that how I aseert quite large number by PHPUnit. I wrote fibonacci number. But in case 100, I wrote below.

http://github.com/sanemat/kata-fibonacci-phpunit/commit/b6b2945d2eff1b95e7e25b8be8c7bff11098d44d

I expect this return TRUE. It failed.

http://www.php.net/manual/en/language.types.float.php

I understood 'never compare for equality.' and so how to aseert it? At the end, I compare with to_string each other. How to compare large number in PHP ?

http://github.com/sanemat/kata-fibonacci-phpunit/commit/70a0e47bc0737be47da8fe8726634edd851d940d

I feel it as bad smell. But I do not know better way. Please tell me how do you assert it?

====
php > $a = 354224848179261915075;
php > echo $a;
3.5422484817926E+20
php > $b = 3.5422484817926E+20;
php > echo $b;
3.5422484817926E+20
php > echo ($a == $b) ? 'TRUE' : 'FALSE';
FALSE
php > echo gmp_cmp($a, $b);
PHP Warning:  gmp_cmp(): Unable to convert variable to GMP - wrong type in php shell code on line 1
php > echo (strval($a) == strval($b)) ? 'TRUE' : 'FALSE';
TRUE
====

environment
$ uname -a
Linux localhost.localdomain 2.6.33.6-147.2.4.fc13.x86_64 #1 SMP Fri Jul 23 17:14:44 UTC 2010 x86_64 x86_64 x86_64 GNU/Linux
$ php --version
PHP 5.3.3 (cli) (built: Jul 22 2010 15:57:00) 
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.3.0, Copyr开发者_开发问答ight (c) 1998-2010 Zend Technologies

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To work with large numbers, there is BCMath libray of PHP.