Re: [PHP-ES] Problema con una simple suma ...

Hola hackob:

2010/4/8 hackob <[email protected]>

> El problema se solucionó cuando modifiqué el parámetro precision en el
> php.ini de 12 a 15, lo curioso es que si pongo 16 el resultado es
> 0.099999999999999998.
>
> Me gustaría saber el por qué ...
>

Copio y pego desde http://php.net/manual/en/language.types.float.php:

The size of a float is platform-dependent, although a maximum of ~1.8e308
with a precision of roughly 14 decimal digits is a common value (the 64 bit
IEEE format).
*Warning*Floating point precision

It is typical that simple decimal fractions like *0.1* or *0.7* cannot be
converted into their internal binary counterparts without a small loss of
precision. This can lead to confusing results: for example, *
floor((0.1+0.7)*10)* will usually return *7*instead of the expected *8*,
since the internal representation will be something like *7.9*.

This is due to the fact that it is impossible to express some fractions in
decimal notation with a finite number of digits. For instance, *1/3* in
decimal form becomes *0.3*.

So never trust floating number results to the last digit, and never compare
floating point numbers for equality. If higher precision is necessary,
the arbitrary
precision math functions <http://php.net/manual/en/ref.bc.php> and
gmp<http://php.net/manual/en/ref.gmp.php> functions
are available.
O sea, si queres una suma de precisión no uses el operador "+" sino la
función "bcadd()" o "gmp_add()". Suerte.

-- 
J. Mauro Daino (tcc: jMd)
* profile: google.com/profiles/maurodaino