Bug #16366 Updated: bit shifting error

ID: 16366 Updated by: adam@adeptsoftware.com Reported By: adam@adeptsoftware.com -Status: Open +Status: Closed -Bug Type: Documentation problem +Bug Type: Math related Operating System: WinXP PHP Version: 4.1.2 New Comment: Well I have 200 groups of 64 on/off's.. I can name the 200 bigint groups but there is no way in hell I am going to name 12,800 bools, not to mention that they would take up 8x more space in the database.. Each group has the same structure - somebody needs to write a DB that uses structures as custom fields. This may be the way they work but this is ancient design - I was surprised as hell when I started learning MySQL and realized that they are still doing things this way. But anyway. Now I am thinking "char binary" since it can be fixed size, but the documentation on PHP's conversions of MySQL is sparse. If someone would like to pursue this in private email please write. The original bug was about bit shifting, which I don't think would involve a conversion to float.. unless PHP is doing something weird. It looks like someone is just not expecting a shift greater than 32. Previous Comments: ------------------------------------------------------------------------ [2002-03-31 13:27:30] sander@php.net Good point. Reopening as documentation problem. ------------------------------------------------------------------------ [2002-03-31 13:23:52] msopacua@idg.nl 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] derick@php.net 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] daniel@php.net 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] daniel@php.net 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. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view 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