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* Bitwise: provide examples of turning bits on and off.

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@278664 c90b9560-bf6c-de11-be94-00142212c4b1
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Daniel Convissor 2009-04-13 16:04:20 +00:00
parent 4bc37ab2c6
commit 2b04b69cc0
1 changed files with 56 additions and 4 deletions
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60
language/operators.xml
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@ -1,5 +1,5 @@
<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.140 $ -->
<!-- $Revision: 1.141 $ -->
<chapter xml:id="language.operators" xmlns="http://docbook.org/ns/docbook">
<title>Operators</title>
<simpara>
@ -441,7 +441,6 @@ $b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";
Right shifts have copies of the sign bit shifted in on the left,
meaning the sign of an operand is preserved.
</para>
<para>
Use parentheses to ensure the desired
<link linkend="language.operators.precedence">precedence</link>.
@ -450,13 +449,66 @@ $b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";
<userinput>($a &amp; $b) == true</userinput> evaluates the bitwise and
then the equivalency.
</para>
<para>
Be aware of data type conversions. If both the left-hand and
right-hand parameters are strings, the bitwise operator will
operate on the characters' ASCII values.
</para>
<para>
<informalexample>
<para>
<literallayout>
PHP's error_reporting ini setting uses bitwise values,
providing a real-world demonstration of turning
bits off. To show all errors, except for notices,
the php.ini file instructions say to use:
<userinput>E_ALL &amp; ~E_NOTICE</userinput>
</literallayout>
</para>
<para>
<literallayout>
This works by starting with E_ALL:
<computeroutput>00000000000000000111011111111111</computeroutput>
Then taking the value of E_NOTICE...
<computeroutput>00000000000000000000000000001000</computeroutput>
... and inverting it via <userinput>~</userinput>:
<computeroutput>11111111111111111111111111110111</computeroutput>
Finally, it uses AND (&amp;) to find the bits turned
on in both values:
<computeroutput>00000000000000000111011111110111</computeroutput>
</literallayout>
</para>
<para>
<literallayout>
Another way to accomplish that is using XOR (<userinput>^</userinput>)
to find bits that are on in only one value or the other:
<userinput>E_ALL ^ E_NOTICE</userinput>
</literallayout>
</para>
</informalexample>
</para>
<para>
<informalexample>
<para>
<literallayout>
error_reporting can also be used to demonstrate turning bits on.
The way to show just errors and recoverable errors is:
<userinput>E_ERROR | E_RECOVERABLE_ERROR</userinput>
</literallayout>
</para>
<para>
<literallayout>
This process combines E_ERROR
<computeroutput>00000000000000000000000000000001</computeroutput>
and
<computeroutput>00000000000000000001000000000000</computeroutput>
using the OR (<userinput>|</userinput>) operator
to get the bits turned on in either value:
<computeroutput>00000000000000000001000000000001</computeroutput>
</literallayout>
</para>
</informalexample>
</para>
<para>
<example>
<title>Bitwise AND, OR and XOR operations on integers</title>