IntMultToLong.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>


<overview>
<p>
An integer multiplication that is assigned
to a variable of type <code>long</code> or returned from a method with 
return type <code>long</code> may cause unexpected arithmetic overflow.
</p>

</overview>
<recommendation>

<p>
Casting to type <code>long</code> before multiplying reduces the risk of arithmetic overflow.
</p>

</recommendation>
<example>

<p>In the following example, the multiplication expression assigned to <code>j</code> causes overflow and results 
in the value <code>-1651507200</code> instead of <code>4000000000000000000</code>.</p>

<sample src="IntMultToLong.java" />

<p>In the following example, the assignment to <code>k</code> correctly avoids overflow by casting 
one of the operands to type <code>long</code>.
</p>

<sample src="IntMultToLongGood.java" />

</example>
<references>


<li>
  J. Bloch and N. Gafter, <em>Java Puzzlers: Traps, Pitfalls, and Corner Cases</em>, Puzzle 3. Addison-Wesley, 2005.
</li>
<li>
  Java Language Specification:
  <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-15.html#jls-15.17.1">Multiplication Operator</a>.
</li>
<li>SEI CERT Oracle Coding Standard for Java:
  <a href="https://wiki.sei.cmu.edu/confluence/display/java/NUM00-J.+Detect+or+prevent+integer+overflow">NUM00-J. Detect or prevent integer overflow</a>.</li>


</references>
</qhelp>