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<HTML><HEAD><TITLE>Recipe 2.9. Making Numbers Even More Random (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:30:13Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch02_01.htm"TITLE="2. Numbers"><LINKREL="prev"HREF="ch02_09.htm"TITLE="2.8. Generating Different Random Numbers"><LINKREL="next"HREF="ch02_11.htm"TITLE="2.10. Generating Biased Random Numbers"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_09.htm"TITLE="2.8. Generating Different Random Numbers"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 2.8. Generating Different Random Numbers"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch02_01.htm"TITLE="2. Numbers"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_11.htm"TITLE="2.10. Generating Biased Random Numbers"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 2.10. Generating Biased Random Numbers"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch02-16587">2.9. Making Numbers Even More Random</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-611">Problem</A></H3><PCLASS="para">You want to generate numbers that are more random than Perl's random numbers. Limitations of your C library's random number generator seeds will sometimes cause problems. The sequence of pseudo-random numbers may repeat too soon for some applications.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-617">Solution</A></H3><PCLASS="para">Use a different random number generator, such as those provided by the <ACLASS="indexterm"NAME="ch02-idx-1000008041-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008041-1"></A>Math::Random and Math::TrulyRandom modules from CPAN:</P><PRECLASS="programlisting">use Math::TrulyRandom;$random = truly_random_value();use Math::Random;$random = random_uniform();</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-633">Discussion</A></H3><PCLASS="para">Perl uses the standard C library routine <EMCLASS="emphasis">rand</EM> (3) to generate pseudo-random numbers. (This can be changed at build time, however.) Some implementations of the <CODECLASS="literal">rand</CODE> function return only 16-bit random numbers or have algorithmic weaknesses and may not be sufficiently random.</P><PCLASS="para">The Math::TrulyRandom module uses the inadequacies of your system's timers to generate the random numbers. This takes a while, so it isn't useful for generating a lot of random numbers.</P><PCLASS="para">The Math::Random module uses the <CODECLASS="literal">randlib</CODE> library to generate random numbers. It also includes a wide range of related functions.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-643">See Also</A></H3><PCLASS="para">The <CODECLASS="literal">srand</CODE> and <CODECLASS="literal">rand</CODE> functions in <EMCLASS="emphasis">perlfunc</EM> (1) and <ACLASS="olink"HREF="../prog/ch03_01.htm">Chapter 3</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>; <ACLASS="xref"HREF="ch02_08.htm"TITLE="Generating Random Numbers">Recipe 2.7</A>; <ACLASS="xref"HREF="ch02_09.htm"TITLE="Generating Different Random Numbers">Recipe 2.8</A>; the documentation for the CPAN modules Math::Random and Math::TrulyRandom <ACLASS="indexterm"NAME="ch02-idx-1000008043-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008043-1"></A></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_09.htm"TITLE="2.8. 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Generating Biased Random Numbers</TD></TR></TABLE><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><FONTSIZE="-1"></DIV<!-- LIBRARY NAV BAR --> <img src="../gifs/smnavbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links"><p> <a href="copyrght.htm">Copyright © 2002</a> O'Reilly & Associates. All rights reserved.</font> </p> <map name="library-map"> <area shape="rect" coords="1,0,85,94" href="../index.htm"><area shape="rect" coords="86,1,178,103" href="../lwp/index.htm"><area shape="rect" coords="180,0,265,103" href="../lperl/index.htm"><area shape="rect" coords="267,0,353,105" href="../perlnut/index.htm"><area shape="rect" coords="354,1,446,115" href="../prog/index.htm"><area shape="rect" coords="448,0,526,132" href="../tk/index.htm"><area shape="rect" coords="528,1,615,119" href="../cookbook/index.htm"><area shape="rect" coords="617,0,690,135" href="../pxml/index.htm"></map> </BODY></HTML>⌨️ 快捷键说明
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