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<title>Bitwise operations</title>
<body bgcolor="#ffffcc">
<hr>
<center>
<h1>Bitwise operations</h1>
</center>
<hr>
<p>
Bitwise operators include:
<p>
<center>
<table border=2 width=40% bgcolor=ivory>
<tr align=center><td>&</td> <td><a href="#aox">AND</a></td></tr>
<tr align=center><td>&=</td> <td><a href="#aox">AND</a></td></tr>
<tr align=center><td>|</td> <td><a href="#aox">OR</a></td></tr>
<tr align=center><td>|=</td> <td><a href="#aox">OR</a></td></tr>
<tr align=center><td>^</td> <td><a href="#aox">XOR</a></td></tr>
<tr align=center><td>^=</td> <td><a href="#aox">XOR</a></td></tr>
<tr align=center><td>~</td> <td><a href="#one">one's compliment</a></td></tr>
<tr align=center><td><<</td> <td><a href="#shift">Shift Left</a></td></tr>
<tr align=center><td><<</td> <td><a href="#shift">Shift Left</a></td></tr>
<tr align=center align=center><td>>>=</td> <td><a href="#shift">Shift Right</a></td></tr>
<tr align=center><td>>>=</td><td><a href="#shift">Shift Right</a></td></tr>
</table>
</center>
<p>
<a name=aox>
<hr>
<h2>AND OR and XOR</h2>
These require two operands and will perform bit comparisions.
<p>
<b>AND &</b>
will copy a bit to the result if it exists in both operands.
<p>
<center>
<table border=2 bgcolor=ivory>
<tr><td>
<pre>
main()
{
unsigned int a = 60; /* 60 = 0011 1100 */
unsigned int b = 13; /* 13 = 0000 1101 */
unsigned int c = 0;
c = a & b; /* 12 = 0000 1100 */
}
</pre>
</td></tr>
</table>
</center>
<p>
<b>OR |</b> will copy a bit if it exists in eather operand.
<p>
<center>
<table border=2 bgcolor=ivory>
<tr><td>
<pre>
main()
{
unsigned int a = 60; /* 60 = 0011 1100 */
unsigned int b = 13; /* 13 = 0000 1101 */
unsigned int c = 0;
c = a | b; /* 61 = 0011 1101 */
}
</pre>
</td></tr>
</table>
</center>
<p>
<b>XOR ^</b> copies the bit if it is set in one operand (but not both).
<p>
<center>
<table border=2 bgcolor=ivory>
<tr><td>
<pre>
main()
{
unsigned int a = 60; /* 60 = 0011 1100 */
unsigned int b = 13; /* 13 = 0000 1101 */
unsigned int c = 0;
c = a ^ b; /* 49 = 0011 0001 */
}
</pre>
</td></tr>
</table>
</center>
<p>
<img src=../../GRAPHICS/computer.gif alt="o">
<a href=../EXAMPLES/swap.c>XOR example program</a> which swaps the contents of two variables.
<p>
<a name=one>
<hr>
<h2>Ones Complement</h2>
This operator is unary (requires one operand) and has the efect of
'flipping' bits.
<p>
<center>
<table border=2 bgcolor=ivory>
<tr><td>
<pre>
main()
{
unsigned int Value=4; /* 4 = 0000 0100 */
Value = ~ Value; /* 251 = 1111 1011 */
}
</pre>
</td></tr>
</table>
</center>
<p>
<a name=shift>
<hr>
<h2>Bit shift.</h2>
The following <a href="../CONCEPT/expressions.html">operators</a>
can be used for shifting bits left or right.
<p>
<center>
<table border=2 width=50% bgcolor=ivory>
<tr align=center>
<td width=25%> << </td>
<td width=25%> >> </td>
<td width=25%> <<= </td>
<td width=25%> >>= </td>
</tr>
</table>
</center>
<p>
The left operands value is moved left or right by the number of bits specified
by the right operand. For example:
<p>
<center>
<table border=2 bgcolor=ivory>
<tr><td>
<pre>
main()
{
unsigned int Value=4; /* 4 = 0000 0100 */
unsigned int Shift=2;
Value = Value << Shift; /* 16 = 0001 0000 */
Value <<= Shift; /* 64 = 0100 0000 */
printf("%d\n", Value); /* Prints 64 */
}
</pre>
</td></tr>
</table>
</center>
<p>
Usually, the resulting 'empty'
bit is assigned ZERO.
Please use
<a href="data_types.html#modifier">unsigned</a>
variables with these operators to avoid unpredictable
results.
<hr>
<h2>Examples:</h2>
<img src=../../GRAPHICS/computer.gif>
<a href="../EXAMPLES/and.c">AND</a><br>
<img src=../../GRAPHICS/computer.gif>
<a href="../EXAMPLES/or.c">OR</a><br>
<img src=../../GRAPHICS/computer.gif>
<a href="../EXAMPLES/bit_shift.c">Bit shifting.</a>
<hr>
<h2>Problem:</h2>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../PROBLEMS/problems.html#binary">Bit shifting problem.</a>
<hr>
<h2>See Also:</h2>
<img src=../../GRAPHICS/whiteball.gif>
All the other <a href="expressions.html#bit">Expressions and operators</a>.<br>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../CONCEPT/precedence.html">Operator precedence.</a><br>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../CONCEPT/assignment.html">Assignment Operators</a>.
<hr>
<p>
<center>
<table border=2 width=80% bgcolor=ivory>
<tr align=center>
<td width=25%>
<a href="../cref.html">Top</a>
</td><td width=25%>
<a href="../master_index.html">Master Index</a>
</td><td width=25%>
<a href="../SYNTAX/keywords.html">Keywords</a>
</td><td width=25%>
<a href="../FUNCTIONS/funcref.htm">Functions</a>
</td>
</tr>
</table>
</center>
<p>
<hr>
<address>Martin Leslie
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