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Bug #13241 round() failed elementary level math
Submitted: 2001-09-10 18:08 UTC Modified: 2001-09-10 18:56 UTC
From: cnewbill at elementalrain dot com Assigned:
Status: Not a bug Package: Math related
PHP Version: 4.0.6 OS: Linux 2.4.x
Private report: No CVE-ID: None
 [2001-09-10 18:08 UTC] cnewbill at elementalrain dot com
[Post from PHP-DEV]

<?php

$x = 10.95;
$y = 0.70;

$e = $x*$y;

print "Discounted price = $e\n";

var_dump($e);

$z = round($e, 2);

var_dump($z);

print "Rounded Price = $z\n";

// this works grrr

$x = round(7.665, 2);

print "Working example of round = $x\n";

?>

Produces

[cnewbill@storm cnewbill]$ php -q t.php
Discounted price = 7.665
float(7.665)
float(7.66)
Rounded Price = 7.66
Working example of round = 7.67
[cnewbill@storm cnewbill]$ php -v
4.0.6

Which is wrong, it should be 7.67.  If I don't do the multiplication and
simply send round 7.665 it works right!!??

Any ideas?

-Chris

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 [2001-09-10 18:55 UTC] jeroen@php.net
Floats are inaccurate, by doing some math on them, you ended up with 7.6649999999999999999 or something, which is correctly rounded DOWN.

Simply don't use floats if it needs to accurate. RTFM on floats, you'll more info there.
 [2001-09-10 18:56 UTC] jeroen@php.net
The language-monster has eaten up my verbs, sorry for that ;-)

  --Jeroen
 
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