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Date: Fri, 02 May 2008 20:36:53 +0200
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Subject: Re: [PHP-DEV] Float comparison
From: stefan.walk@gmail.com (Stefan Walk)

Todd Ruth schrieb:
> I'm afraid you'll find Pierre's response representative.  The
> php devs seem to consider the fact that a theoretically perfect
> "==" doesn't exist to mean that the improvements that would 
> cover 99.9% of user issues with float == shouldn't be made.
> 
> It could be worse, however.  At least the cast to string works
> as one would expect.  Just imagine if those who oppose
> improving "==" had their logic extended to the cast to string.
> Php might to the following:
> 
> <?php
> $x=.3+.4+.5;
> print "$x\n";
> ?>
> 
> might output "1.19999999999999996447286321199499070644378662109375"
> 
> If someone filed a bug report, they could refer you to that
> paper and tell you there's no bug because you're trying to get
> a string from float and you never know what you might get.

Actually, depending on ini settings, that happens:

$ php -dprecision=100 -r 'echo 0.3+0.4+0.5,"\n";'
1.1999999999999999555910790149937383830547332763671875

Don't echo floats, use printf() or alike.

And you'll quickly see that the "cast to string before comparision" is a 
bad idea, because:
$ php -dprecision=1 -r 'var_dump((string)1.4 == (string)1.1);'
bool(true)

Having display settings affect comparisions seems like a really bad idea 
to me ;)

Regards,
Stefan