mirror of
https://github.com/github/codeql.git
synced 2026-04-10 01:24:02 +02:00
e21cbe82a9
Where possible update Java documentation links to Java 11. Additionally update some other links to use HTTPS.
47 lines
1.4 KiB
XML
47 lines
1.4 KiB
XML
<!DOCTYPE qhelp PUBLIC
|
|
"-//Semmle//qhelp//EN"
|
|
"qhelp.dtd">
|
|
<qhelp>
|
|
|
|
|
|
<overview>
|
|
<p>Checking whether the result of a bitwise operation is greater than zero may yield unexpected results.
|
|
</p>
|
|
|
|
</overview>
|
|
<recommendation>
|
|
|
|
<p>It is more robust to check whether the result of the bitwise operation is <i>non-zero</i>.</p>
|
|
|
|
</recommendation>
|
|
<example>
|
|
|
|
<p>In the following example, the expression assigned to variable <code>bad</code> is <i>not</i> a robust way to check
|
|
that the <code>n</code>th bit of <code>x</code> is set.
|
|
With the given values of <code>x</code> (all bits are set) and <code>n</code>,
|
|
the expression <code>x & (1<<n)</code> has the value <code>-2147483648</code>,
|
|
and the variable <code>bad</code> is assigned <code>false</code>,
|
|
even though the 31st bit of <code>x</code> is, in fact, set.
|
|
</p>
|
|
|
|
<sample src="BitwiseSignCheck.java" />
|
|
|
|
<p>In the following example, the expression assigned to variable <code>good</code> is a robust way to check that the
|
|
<code>n</code>th bit of <code>x</code> is set. With the given values of <code>x</code> and
|
|
<code>n</code>, the variable <code>good</code> is assigned <code>true</code>.</p>
|
|
|
|
<sample src="BitwiseSignCheckGood.java" />
|
|
|
|
</example>
|
|
<references>
|
|
|
|
|
|
<li>
|
|
Java Language Specification:
|
|
<a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-15.html#jls-15.22.1">Integer Bitwise Operators &, ^, and |</a>.
|
|
</li>
|
|
|
|
|
|
</references>
|
|
</qhelp>
|