note 119860 added to language.types.float

In the gettype() manual, it says "(for historical reasons "double" is returned in case of a float, and not simply "float") ". However, I think that internally PHP sometimes uses the C double definition (i.e. a double is twice the size of a float/real). See the example below: <? //Function required to reverse a string on blocks of two function strrev_x($s, $x = 2) { if ($x <= 1) { return strrev($s); } else { return (implode(array_reverse(array_map('implode', array_chunk(str_split($s), $x))))); } } echo 'double pack'. PHP_EOL; $tst = pack('d', '1.6'); var_dump(strrev_x(bin2hex($tst))); $tst = pack('d', 8-6.4); var_dump(strrev_x(bin2hex($tst))); echo 'float pack'. PHP_EOL; $tst = pack('f', '1.6'); var_dump(strrev_x(bin2hex($tst))); $tst = pack('f', 8-6.4); var_dump(strrev_x(bin2hex($tst))); ?> (The strrev_x-bin2hex combination is just to give printable characters.) Given that PHP treats doubles and floats identically, I'd expected the same string as output, however, the output is: double pack string(16) "3ff999999999999a" //Here you see that there is a minute difference... string(16) "3ff9999999999998" float pack string(8) "3fcccccd" //... which doesn't exist here string(8) "3fcccccd" So, as an alternative to using $float1 === $float2 one could use pack('f', $float1) === pack ('f', $float2) with a big footnote that one should really remember that one is *reducing* your accuracy of the comparison. AFAIK is this the only way (apart from epsilon methods) to securely compare two floats. ---- Server IP: 72.52.91.14 Probable Submitter: 31.161.105.18 ---- Manual Page -- http://php.net/manual/en/language.types.float.php Edit -- https://master.php.net/note/edit/119860 Del: integrated -- https://master.php.net/note/delete/119860/integrated Del: useless -- https://master.php.net/note/delete/119860/useless Del: bad code -- https://master.php.net/note/delete/119860/bad+code Del: spam -- https://master.php.net/note/delete/119860/spam Del: non-english -- https://master.php.net/note/delete/119860/non-english Del: in docs -- https://master.php.net/note/delete/119860/in+docs Del: other reasons-- https://master.php.net/note/delete/119860 Reject -- https://master.php.net/note/reject/119860 Search -- https://master.php.net/manage/user-notes.php