Doc #53365 [Opn->Csd]: Inaccurate information on floats.

Edit report at http://bugs.php.net/bug.php?id=53365&edit=1 ID: 53365 Updated by: cataphract@php.net Reported by: phplists at stanvassilev dot com Summary: Inaccurate information on floats. -Status: Open +Status: Closed Type: Documentation Problem Package: Documentation problem Operating System: - PHP Version: Irrelevant -Assigned To: +Assigned To: cataphract Block user comment: N Private report: N New Comment: This bug has been fixed in the documentation's XML sources. Since the online and downloadable versions of the documentation need some time to get updated, we would like to ask you to be a bit patient. Thank you for the report, and for helping us make our documentation better. Previous Comments: ------------------------------------------------------------------------ [2010-11-20 17:10:06] cataphract@php.net Automatic comment from SVN on behalf of cataphract Revision: http://svn.php.net/viewvc/?view=revision&revision=305581 Log: - Fixed inaccurate information on floats. Closes bug #53365. ------------------------------------------------------------------------ [2010-11-20 13:24:34] phplists at stanvassilev dot com Description: ------------ http://php.net/manual/en/language.types.float.php The "Warning: Floating point precision" box has misleading information that is partly based on facts, but not well interpreted to the reader: Commenting per paragraph and offering replacement: "It is typical that simple decimal fractions like 0.1 or 0.7 cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9." This is mostly correct, but I'd change the last sentence to "since the internal binary representation of 0.7 is approximately 0.69999..., causing 0.1 + 0.7 to be approximately 0.79999...." -- "This is due to the fact that it is impossible to express some fractions in decimal notation with a finite number of digits. For instance, 1/3 in decimal form becomes 0.3." This is totally off, and more than one users assumed PHP has *wildly* inaccurate floats that would literally represent 1/3 as 0.3 (it's actually ~0.33333333333333331482961625624739) and mixes up periodic decimal fractions with problems of converting decimal float to binary float and back. It's also redundant with the previous paragraph, I'd remove that sentence. -- "So never trust floating number results to the last digit, and never compare floating point numbers for equality. If higher precision is necessary, the arbitrary precision math functions and gmp functions are available." That's ok. ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/bug.php?id=53365&edit=1