Rounding in PHP

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In the PHP documentation, there where talk about integers and, in particular, about the translation to int from float, saying that rounding is toward zero and give you an example:

<?php<br/>echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>

And it really takes 7.
If you do

echo (int) ( (0.2+0.7) * 10 )

It already displays 9.

I understand that in the first case, eight is the number 7.999999 that as a result of rounding becomes seven.

Question(s) in the following:
  1. On all cars will have such results?
  2. Is this normal?
by | 40 views

7 Answers

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1. Yes. And on different platforms and with different compilers/interpreters (see answer barmaley_exe above).
2. Okay.
Google "floating point/comma" or read at least Wikipedia — much will become clear.
If you do not like, try to learn it.
\r
PS
\r
$ perl -e "print int((0.1+0.7) * 10)" 7 $ perl -e "print int((0.1+0.7) * 10)" 9 $ perl-v This is perl, v5.10.1 (*) built for i386-freebsd ...
by
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Where IEEE754 rules in terms of real numbers, must be so.
by
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As I understand it, on the fingers this behaviour can be explained by the fact that 0.1 is not represented in the binary system as a finite fraction, and therefore is truncated in the translation.
by
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7...
by
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Yes, true.
While on the other hand, who knows how castes in page leads? :)
\rb@thinkpad:~$ php -R ' echo (int) ( (0.1+0.7) * 10 ),"\";'
7
b@thinkpad:~$ php -R ' echo (int) ( (0.2+0.7) * 10 ),"\";'
9
b@thinkpad:~$ php-v
PHP 5.3.2-1ubuntu4.5 with Suhosin-Patch (cli) (built: Sep 17 2010 13:41:55)
Copyright © 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright © 1998-2010 Zend Technologies
\r
by
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If you explain approximately, any real number is represented in memory with a certain, not absolute, accuracy (i.e., up to a certain bit).
\r
$ perl -e "printf('%.45f',0.1)" 0.100000000000000005551115123125782702118158340 $ perl -e "printf('%.45f',0.7)" 0.699999999999999955591079014993738383054733276 $ ruby -e "printf('%.45f',0.8)" 0.800000000000000044408920985006261616945266724
by
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For proper rounding you can use round()
by

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