Edit report at http://bugs.php.net/bug.php?id=54479&edit=1
ID: 54479
Comment by: for-bugs at hnw dot jp
Reported by: for-bugs at hnw dot jp
Summary: round(1e15+0.1) returns 1e15+0.1 instead of 1e15
Status: Bogus
Type: Bug
Package: Math related
Operating System: any
PHP Version: 5.3.6
Block user comment: N
Private report: N
New Comment:
My test script seems to be wrong. How about next one?
<?php
ini_set("precision",19);
var_dump(1000000000000000.125);
// float(1000000000000000.125)
var_dump(round(1000000000000000.125));
// PHP 5.3.6 returns float(1000000000000000.125)
// PHP 5.2.17 returns float(1000000000000000)
IEEE 754 double precision have 53 bit fractions, so 1000000000000000 and
1000000000000000.125 is exact number.
This behavior is caused by ext/standard/math.c:160-163
/* This value is beyond our precision, so rounding it is pointless
*/
if (fabs(tmp_value) >= 1e15) {
return value;
}
Previous Comments:
------------------------------------------------------------------------
[2011-04-06 19:39:39] [email protected]
Floating point values have a limited precision. Hence a value might
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly
printing it without any mathematical operations.
If you would like to know more about "floats" and what IEEE
754 is, read this:
http://www.floating-point-gui.de/
Thank you for your interest in PHP.
.
------------------------------------------------------------------------
[2011-04-06 19:22:45] for-bugs at hnw dot jp
Description:
------------
When round() is called with 1 argument which value is between 1e15 and
2^53, round() returns non-rounded value even if the value has fractional
part.
For instance, though 1e15 is exact number as IEEE 754 double precision,
round(1e15+0.1) returns 1e15+0.1. I think 1e15 is better result.
Test script:
---------------
<?php
'ini_set("precision",18);
var_dump(round(1000000000000000.1));
Expected result:
----------------
float(1000000000000000)
Actual result:
--------------
float(1000000000000000.12)
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/bug.php?id=54479&edit=1
