Re: [PHP-DEV] PHP 4.0 Bug #9411 Updated: Arithmetic error From: Derick Rethans (d.rethans <email protected>)
Date: 02/22/01

Hi,

can't we make this a FAQ?
(if I get no response, it's in the FAQ in 60 mins :)

Derick

On 22 Feb 2001 lyric <email protected> wrote:

> ID: 9411
> Updated by: lyric
> Reported By: robburne <email protected>
> Old-Status: Closed
> Status: Bogus
> Old-Bug Type: *Regular Expressions
> Bug Type: Math related
> Assigned To:
> Comments:
>
> This is nothing to do with PHP, its just part of the way computers store floating-point numbers. It stores an aproximation of 0.32, as close as it can get, but when you start multiplying it, the little difference between 0.32 and what it stored starts to get magnified.
>
> BTW, 5.5511151231258E-17 is 0.000000000000000055511151231258 which is *really* closed to 0.
>
> If you want to output formatted numbers, you should either round it, or use printf()
> http://www.php.net/manual/en/function.printf.php
>
>
> Previous Comments:
> ---------------------------------------------------------------------------
>
> [2001-02-22 16:05:47] derick <email protected>
> This is normal floating point math behavior
>
> ---------------------------------------------------------------------------
>
> [2001-02-22 15:45:55] robburne <email protected>
> Hi I am not sure if I have found a bug - what do you think.......?
>
> Consider this:
>
> $var1 = -0.32 + (0.1*3.2)
>
> This should give var1 the value 0, instead it gives
>
> 5.5511151231258E-17
>
> Interestingly if you increase -0.33 and 3.3 respectively it gives the correct answer. Werid!
>
> Rob Burne
>
> robburne <email protected>
>
>
> ---------------------------------------------------------------------------
>
>
>
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Derick Rethans

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