diff options
Diffstat (limited to 'reference/C/CONCEPT/bitwise.html')
| -rw-r--r-- | reference/C/CONCEPT/bitwise.html | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/reference/C/CONCEPT/bitwise.html b/reference/C/CONCEPT/bitwise.html new file mode 100644 index 0000000..82c2aca --- /dev/null +++ b/reference/C/CONCEPT/bitwise.html @@ -0,0 +1,231 @@ +<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 +<script language="JavaScript"> +<!-- // +document.write(document.lastModified); +// --> +</script> +</address> + + + + + + + + + |