Bug #54985 [NEW]: round doesn't work with non-14 precision

From: Date: Fri, 03 Jun 2011 14:10:15 +0000
Subject: Bug #54985 [NEW]: round doesn't work with non-14 precision
Groups: php.bugs 
Request: Send a blank email to php-bugs+get-161159@lists.php.net to get a copy of this message 
From:             
Operating system: n/a
PHP version:      5.3.6
Package:          *Math Functions
Bug Type:         Bug
Bug description:round doesn't work with non-14 precision

Description:
------------
Round() doesn't work right when the precision is set to e.g. 16.

The last comment in #51701 also makes notice of this. (However it seems
unrelated to that bugreport.)

Bug #5500 states that you shouldn't set the precision higher than the
data-type can hold. If that's still true I think we should add a warning
when setting the precision too high instead of just accepting it and trying
to work it out.

_php_math_round in ext/standard/math.c cites:
  if ((precision_places = php_intlog10abs(value)) > 0) {
    precision_places = 14 - php_intlog10abs(value);
  } else {
    precision_places = 14;
  }

and I guess 14 shouldn't be hardcoded there.

Test script:
---------------
php > ini_set('precision', 30);
php > var_dump(round((5.5/100), 3));

Expected result:
----------------
float(0.055)


Actual result:
--------------
float(0.0550000000000000002775557561563)


-- 
Edit bug report at http://bugs.php.net/bug.php?id=54985&edit=1
-- 
Try a snapshot (PHP 5.2):            http://bugs.php.net/fix.php?id=54985&r=trysnapshot52
Try a snapshot (PHP 5.3):            http://bugs.php.net/fix.php?id=54985&r=trysnapshot53
Try a snapshot (trunk):              http://bugs.php.net/fix.php?id=54985&r=trysnapshottrunk
Fixed in SVN:                        http://bugs.php.net/fix.php?id=54985&r=fixed
Fixed in SVN and need be documented: http://bugs.php.net/fix.php?id=54985&r=needdocs
Fixed in release:                    http://bugs.php.net/fix.php?id=54985&r=alreadyfixed
Need backtrace:                      http://bugs.php.net/fix.php?id=54985&r=needtrace
Need Reproduce Script:               http://bugs.php.net/fix.php?id=54985&r=needscript
Try newer version:                   http://bugs.php.net/fix.php?id=54985&r=oldversion
Not developer issue:                 http://bugs.php.net/fix.php?id=54985&r=support
Expected behavior:                   http://bugs.php.net/fix.php?id=54985&r=notwrong
Not enough info:                     http://bugs.php.net/fix.php?id=54985&r=notenoughinfo
Submitted twice:                     http://bugs.php.net/fix.php?id=54985&r=submittedtwice
register_globals:                    http://bugs.php.net/fix.php?id=54985&r=globals
PHP 4 support discontinued:          http://bugs.php.net/fix.php?id=54985&r=php4
Daylight Savings:                    http://bugs.php.net/fix.php?id=54985&r=dst
IIS Stability:                       http://bugs.php.net/fix.php?id=54985&r=isapi
Install GNU Sed:                     http://bugs.php.net/fix.php?id=54985&r=gnused
Floating point limitations:          http://bugs.php.net/fix.php?id=54985&r=float
No Zend Extensions:                  http://bugs.php.net/fix.php?id=54985&r=nozend
MySQL Configuration Error:           http://bugs.php.net/fix.php?id=54985&r=mysqlcfg

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