note 105821 added to language.operators.bitwise

The NOT or complement operator ( ~ ) and negative binary numbers can be confusing. ~2 = -3 because you use the formula ~x = -x - 1 The bitwise complement of a decimal number is the negation of the number minus 1. NOTE: just using 4 bits here for the examples below but in reality PHP uses 32 bits. Converting a negative decimal number (ie: -3) into binary takes 3 steps: 1) convert the positive version of the decimal number into binary (ie: 3 = 0011) 2) flips the bits (ie: 0011 becomes 1100) 3) add 1 (ie: 1100 + 0001 = 1101) You might be wondering how does 1101 = -3. Well PHP uses the method "2's complement" to render negative binary numbers. If the left most bit is a 1 then the binary number is negative and you flip the bits and add 1. If it is 0 then it is positive and you don't have to do anything. So 0010 would be a positive 2. If it is 1101, it is negative and you flip the bits to get 0010. Add 1 and you get 0011 which equals -3. ---- Server IP: 69.147.83.197 Probable Submitter: 68.227.80.11 ---- Manual Page -- http://www.php.net/manual/en/language.operators.bitwise.php Edit -- https://master.php.net/note/edit/105821 Del: integrated -- https://master.php.net/note/delete/105821/integrated Del: useless -- https://master.php.net/note/delete/105821/useless Del: bad code -- https://master.php.net/note/delete/105821/bad+code Del: spam -- https://master.php.net/note/delete/105821/spam Del: non-english -- https://master.php.net/note/delete/105821/non-english Del: in docs -- https://master.php.net/note/delete/105821/in+docs Del: other reasons-- https://master.php.net/note/delete/105821 Reject -- https://master.php.net/note/reject/105821 Search -- https://master.php.net/manage/user-notes.php