Description:
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The behavior of function round() was changed with revision 301991. So when a small number is rounded to small precision, round() of PHP5.3.4-5.3.6 returns different value from PHP5.3.0-5.3.3. Additionally, the current behavior is different from referred RFC(*1). I suppose it is not intended change.

For example, test script returns "float(4.0E-60)" for PHP 5.3.0-5.3.3 and PHP 5.2.17. However, PHP 5.3.4-5.3.6 shows "float(3.0E-60)".

This behavior changing was affected with revision 301991(*2) for fixing Bug #52550(*3). However, I think this fix was useless.

Bug #52550 reports probability for integer overflow/underflow. However, the C function php_intlog10abs() returns integer between -324 and 308 because of property for IEEE754 64bit floating point numbers, so overflow/underflow never occur for this part.

*1 http://wiki.php.net/rfc/rounding
*2 http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/standard/math.c?r1=301991&r2=301990&pathrev=301991
*3 http://bugs.php.net/bug.php?id=52550

Test script:
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<?php
var_dump(round(3.5e-60, 60));

Expected result:
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float(4.0E-60)

Actual result:
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float(3.0E-60)