Bug #62465 [Nab]: intval of floats
Edit report at https://bugs.php.net/bug.php?id=62465&edit=1
ID: 62465
Updated by: rasmus@php.net
Reported by: fabrizio at queensboro dot com
Summary: intval of floats
Status: Not a bug
Type: Bug
Package: *General Issues
Operating System: FreeBSD 9.0-RELEASE - amd64
PHP Version: 5.4.4
Block user comment: N
Private report: N
New Comment:
Well, that is just because your output precision is set low enough so when the
value is printed it prints as 895. Try adding this to the top of your test
script:
ini_set('precision',32);
And no, this isn't a modern language vs. old language thing.
For example, in Python:
Python 2.7.3 (default, Apr 20 2012, 22:39:59)
>>> a=8.9500
>>> print a*100
895.0
>>> from math import floor
>>> print floor(a*100)
894.0
The way to fix this is to use arbitrary precision math routines and every
scripting language, including PHP (see gmp, bcmath) provides those, but they are
so much slower than the cpu-provided floating routines that it is hard to
justify.
Previous Comments:
------------------------------------------------------------------------
[2012-07-02 18:23:53] fabrizio at queensboro dot com
correct misspelled OS
------------------------------------------------------------------------
[2012-07-02 18:23:01] fabrizio at queensboro dot com
Very interesting.
Thank you for your link, I always assumed that this was an issue for old
languages and that new ones would have corrected the conversion to integer using
some sort of checking against the "to_string" (I am saying this without knowing
what it takes or what the code looks like).
As you can see here, the code knows that the value is a float(895), without
decimals, so the integer should be the same, else I would expect an output like
float(894.99999999...) during the var_dump.
<?php
$grand_total = '8.9500';
var_dump(
$grand_total,
$grand_total*100,
round($grand_total*100),
intval($grand_total*100)
);
?>
string(6) "8.9500"
float(895)
float(895)
int(894)
------------------------------------------------------------------------
[2012-07-02 16:47:24] rasmus@php.net
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.
You are going to want to round() and not truncate here.
------------------------------------------------------------------------
[2012-07-02 16:30:12] fabrizio at queensboro dot com
Description:
------------
Converting from a float to an integer doesn't always return the correct values.
Try this code:
<?php
$grand_total = 8.9500;
$amount = intval($grand_total*100);
var_dump($amount, $grand_total*100, (int)($grand_total*100));
?>
This will output:
int(894)
float(895)
int(894)
when I would expect:
int(895)
float(895)
int(895)
Test script:
---------------
<?php
$grand_total = 8.9500;
$amount = intval($grand_total*100);
var_dump($amount, $grand_total*100, (int)($grand_total*100));
?>
Expected result:
----------------
int(895)
float(895)
int(895)
Actual result:
--------------
int(894)
float(895)
int(894)
------------------------------------------------------------------------
--
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