Bug #18157 Updated: precision ini value affects internal calculations too

ID: 18157 Updated by: cnovak@gmx.net Reported By: cnovak@gmx.net -Status: Bogus +Status: Open Bug Type: Math related Operating System: Windows XP Pro PHP Version: 4.2.1 New Comment: chg. status Previous Comments: ------------------------------------------------------------------------ [2002-07-04 05:25:10] cnovak@gmx.net I know that the variable is an integer and that the float/double cast is only an internal way of PHP handling larger integers. The manual (http://www.php.net/manual/en/language.types.integer.php) states the following: Integer overflow If you specify a number beyond the _bounds_ of the integer type, it will be interpreted as a float instead. Also, if you perform an operation that results in a number beyond the bounds of the integer type, a float will be returned instead. -- I would assume from the above detail that PHP would cast my variable from int to float when reaching the 32bit boundary. I understand that beyond 2^63 that my number will be incorrect. The strange issue is that this works correctly until 2^47. When precision is set to 20, it works as expected. Since the pow(2, int) does not create any fractions I would assume that the casting works as expected. Same happens using a left bit shift. ------------------------------------------------------------------------ [2002-07-04 04:38:29] sander@php.net PHP can't handle numbers larger than 2^32. Use the gmp or bcmath extension. (the ini setting precision is only for floats (both calculating and printing), you're talking about integers). ------------------------------------------------------------------------ [2002-07-04 04:31:37] cnovak@gmx.net By default precision in php.ini is set to 14 significant digits. I would assume, that this is for printing float results only. Instead, the precision argument is used for storing values in databases too. Check the following code: 01 for ($x = 0; $x < 64; $x++) { 02 $group_bitfield = pow(2, $x); 03 print " $group_bitfield<br>"; 04 } The above yields precision errors at 2^48, 2^49, 2^51, 2^52, 2^54. If this is for output only, fine. But the issue is that these values are also _incorrectly_ stored in an INT(20) field on MySQL. Explicit type casting does not help either. Using arbitrary math is not an option for speed and availabilty at various ISP's. Configuration: WINNT Apache/1.3.26 (Win32) mod_ssl/2.8.10 OpenSSL/0.9.6d PHP version: 4.2.1 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=18157&edit=1