ID: 16366
Updated by: [EMAIL PROTECTED]
Reported By: [EMAIL PROTECTED]
-Status: Closed
+Status: Open
-Bug Type: Math related
+Bug Type: Documentation problem
Operating System: WinXP
PHP Version: 4.1.2
New Comment:
Good point. Reopening as documentation problem.
Previous Comments:
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[2002-03-31 13:23:52] [EMAIL PROTECTED]
Related to the bug only:
<?php
$int=2;
for($i=25;$i<33;$i++)
{
$check=pow($int, $i);
$check2=(int)$check;
$check2 += 1;
$check3=(int)$check;
$check3 -= 1;
echo("i is $i\n");
var_dump($check);
var_dump($check2);
var_dump($check3);
echo("\n");
}
?>
Gives some weird results:
$ ./test_float_conversion.php
i is 25
int(33554432)
int(33554433)
int(33554431)
i is 26
int(67108864)
int(67108865)
int(67108863)
i is 27
int(134217728)
int(134217729)
int(134217727)
i is 28
int(268435456)
int(268435457)
int(268435455)
i is 29
int(536870912)
int(536870913)
int(536870911)
i is 30
int(1073741824)
int(1073741825)
int(1073741823)
i is 31
float(2147483648)
int(-2147483647)
float(-2147483649)
i is 32
float(4294967296)
int(1)
int(-1)
I guess the manual should be appended, in the 'typecasting' section, to
not cast to integer, when it's larger than 2^30 and that those numbers
are automatically converted to floats.
(http://www.php.net/manual/en/language.types.type-juggling.php#language.types.typecasting)
------------------------------------------------------------------------
[2002-03-31 13:10:38] [EMAIL PROTECTED]
Can you please stop this discussion in the bug system. Fighting about
what is best can be done in private mail just fine.
Derick
------------------------------------------------------------------------
[2002-03-31 13:09:00] [EMAIL PROTECTED]
I'm sorry, but this is not flipcode.com - this is web-development.
Not performance, but maintaineability and readability are crucial.
Always write your code in a way someone else could easily understand
what you are trying to do (even if you'll never release your
sourcecode).
------------------------------------------------------------------------
[2002-03-31 12:58:54] [EMAIL PROTECTED]
But "32 columns" are the way databases work. You can give names to
these columns and everybody will understand what they are good for.
- If you decide to just have a (int)flags in SQL, how could someone
possibly understand this without reading your documentation (if you
wrote it) or reading through your source code?
- Databases are meant to have columns - commands such as WHERE, ORDER
BY etc.. only work on columns, but not on your homebrewn data format.
- You can add or remove columns, but modifying your flags would end in
a big mess.
- Databases can optimize/cache requests on certain columns (at least I
think they can).
- Using columns is less error-prone.
Why the hell should you STILL be using your custom-made flags-thingie
instead?
But you are right and the bug still exists. PHP has problems with
floating point operations - that's why I suggested to use the "BC"
package.
I wrote a "BC wrapper" which wraps all BC functions to regular PHP
functions. It is meant for people who want to develop their code with
BC, but still want to keep compatibility to PHP installations without
BC. Tell me if you want it.
------------------------------------------------------------------------
[2002-03-31 12:50:00] [EMAIL PROTECTED]
Daniel: 32 columns or 1 integer, I'd take the integer anytime.
The problem is, that large integers are converted to floats:
<?php
$number=11;
$bigint=$number * 10000000000000000000000000000000;
$bigint_nocalc=1100000000000000000000000000000000;
echo("Using values: $number - $bigint - $bigint_nocalc\n");
var_dump($number);
var_dump($bigint);
var_dump($bigint_nocalc);
echo ("\nNumber shift 34\n");
echo ($number>>34);
echo ("\nNumber shift 2\n");
echo ($number>>2);
echo("\nBigint shift 29\n");
echo($bigint>>29);
echo("\nBigint shift 30\n");
echo($bigint>>30);
echo("\nBigint shift 31\n");
echo($bigint>>31);
echo("\nBigint shift 32\n");
echo($bigint>>32);
echo("\nBigint shift 33\n");
echo($bigint>>33);
echo("\nBigint shift 1\n");
echo($bigint>>1);
?>
Output:
$ ./test_bit.php
Using values: 11 - 1.1E+32 - 1.1E+33
int(11)
float(1.1E+32)
float(1.1E+33)
Number shift 34
2
Number shift 2
2
Bigint shift 29
0
Bigint shift 30
0
Bigint shift 31
0
Bigint shift 32
0
Bigint shift 33
0
Bigint shift 1
0
------------------------------------------------------------------------
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the rest of the comments, please view the bug report online at
http://bugs.php.net/16366
--
Edit this bug report at http://bugs.php.net/?id=16366&edit=1
