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<html>
<head>
<title>
A Tour of NTL: Examples: Floating Point Classes </title>
</head>
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<h1>
<p align=center>
A Tour of NTL: Examples: Floating Point Classes
</p>
</h1>
<p> <hr> <p>
NTL also supports arbitrary precision floating point with
the class <tt>RR</tt>.
Additionally, it supports two specialized classes: <tt>quad_float</tt>,
which gives a form of quadruple precision, but without an extended
exponent range,
and <tt>xdouble</tt>,
which gives double precision, but with an extended exponent range.
The advantage of the latter two classes is efficiency.
<p>
Here again is a program that reads a list of numbers from the input,
and outputs the sum of their squares, using the class <tt>RR</tt>.
<!-- STARTPLAIN
#include <NTL/RR.h>
using namespace std;
using namespace NTL;
int main()
{
RR acc, val;
acc = 0;
while (cin >> val)
acc += val*val;
cout << acc << "\n";
}
ENDPLAIN -->
<!-- STARTPRETTY {{{ -->
<p><p><table cellPadding=10px><tr><td><font color="#000000"><font face="monospace">
<font color="#1773cc">#include </font><font color="#4a6f8b"><NTL/RR.h></font><br>
<br>
<font color="#b02f60"><b>using</b></font> <font color="#008b00"><b>namespace</b></font> std;<br>
<font color="#b02f60"><b>using</b></font> <font color="#008b00"><b>namespace</b></font> NTL;<br>
<br>
<font color="#008b00"><b>int</b></font> main()<br>
{<br>
RR acc, val;<br>
<br>
acc = <font color="#ff8b00">0</font>;<br>
<font color="#b02f60"><b>while</b></font> (cin >> val) <br>
acc += val*val;<br>
<br>
cout << acc << <font color="#4a6f8b">"</font><font color="#8a2ae2">\n</font><font color="#4a6f8b">"</font>;<br>
}<br>
</font></font></td></tr></table><p><p>
<!-- }}} ENDPRETTY -->
<p>
The precision used for the computation can be set by executing
<!-- STARTPLAIN
RR::SetPrecision(p);
ENDPLAIN -->
<!-- STARTPRETTY {{{ -->
<p><p><table cellPadding=10px><tr><td><font color="#000000">
<font face="monospace">
RR::SetPrecision(p);<br>
</font>
</font></td></tr></table><p><p>
<!-- }}} ENDPRETTY -->
which sets the effective precision to <tt>p</tt> bits.
By default, <tt>p=150</tt>.
All of the basic arithmetic operations compute their results
by rounding to the nearest <tt>p</tt>-bit floating point number.
The semantics of this are exactly the same as in the IEEE floating
point standard (except that there are no special values, like
"infinity" and "not a number").
<p>
The number of <i>decimal</i> digits of precision that are used when
printing an <tt>RR</tt> can be set be executing
<!-- STARTPLAIN
RR::SetOutputPrecision(d);
ENDPLAIN -->
<!-- STARTPRETTY {{{ -->
<p><p><table cellPadding=10px><tr><td><font color="#000000">
<font face="monospace">
RR::SetOutputPrecision(d);<br>
</font>
</font></td></tr></table><p><p>
<!-- }}} ENDPRETTY -->
which sets the output precision to <tt>d</tt>.
By default, <tt>d=10</tt>.
<p>
See <a href="RR.cpp.html"><tt>RR.txt</tt></a> for details.
<p>
By replacing the occurences of <tt>RR</tt> by either <tt>quad_float</tt>
or <tt>xdouble</tt>, one gets an equivalent program using one of the
other floating point classes.
The output precision for these two classes can be controlled just
as with <tt>RR</tt>.
See <a href="quad_float.cpp.html"><tt>quad_float.txt</tt></a> and
<a href="xdouble.cpp.html"><tt>xdouble.txt</tt></a>
for details.
<p>
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