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authorTobias Klauser <tklauser@distanz.ch>2008-01-27 11:37:44 +0100
committerTobias Klauser <tklauser@xenon.tklauser.home>2008-01-27 11:37:44 +0100
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+<TITLE>rand</TITLE>
+<body bgcolor="#ffffcc">
+<hr>
+<pre>
+
+
+
+<h3>RAND(3) Linux Programmer's Manual RAND(3)
+</h3>
+
+<h3>NAME
+</h3> rand, srand - random number generator.
+
+<h3>SYNOPSIS
+</h3> #include &lt;stdlib.h&gt;
+
+ int rand(void);
+
+ void srand(unsigned int seed);
+
+<h3>DESCRIPTION
+</h3> The rand() function returns a pseudo-random integer
+ between 0 and RAND_MAX.
+
+ The srand() function sets its argument as the seed for a
+ new sequence of pseudo-random integers to be returned by
+ rand(). These sequences are repeatable by calling srand()
+ with the same seed value.
+
+ If no seed value is provided, the rand() function is auto-
+ matically seeded with a value of 1.
+
+<h3>RETURN VALUE
+</h3> The rand() function returns a value between 0 and
+ RAND_MAX. The srand() returns no value.
+
+<h3>NOTES
+</h3> The versions of rand() and srand() in the Linux C Library
+ use the same random number generator as random() and sran-
+ dom(), so the lower-order bits should be as random as the
+ higher-order bits. However, on older rand() implementa-
+ tions, the lower-order bits are much less random than the
+ higher-order bits.
+
+ In Numerical Recipes in C: The Art of Scientific Computing
+ (William H. Press, Brian P. Flannery, Saul A. Teukolsky,
+ William T. Vetterling; New York: Cambridge University
+ Press, 1990 (1st ed, p. 207)), the following comments are
+ made:
+ "If you want to generate a random integer between 1
+ and 10, you should always do it by
+
+ j=1+(int) (10.0*rand()/(RAND_MAX+1.0));
+
+ and never by anything resembling
+
+ j=1+((int) (1000000.0*rand()) % 10);
+
+ (which uses lower-order bits)."
+
+ Random-number generation is a complex topic. The Numeri-
+ cal Recipes in C book (see reference above) provides an
+ excellent discussion of practical random-number generation
+ issues in Chapter 7 (Random Numbers).
+
+
+
+<h3>GNU 18 May 1995 1
+</h3>
+
+
+
+
+<h3>RAND(3) Linux Programmer's Manual RAND(3)
+</h3>
+
+ For a more theoretical discussion which also covers many
+ practical issues in depth, please see Chapter 3 (Random
+ Numbers) in Donald E. Knuth's The Art of Computer Program-
+ ming, volume 2 (Seminumerical Algorithms), 2nd ed.; Read-
+ ing, Massachusetts: Addison-Wesley Publishing Company,
+ 1981.
+
+<h3>CONFORMING TO
+</h3> SVID 3, BSD 4.3, ISO 9899
+
+</pre>
+<hr>
+<h3>SEE ALSO
+</h3><p>
+<a href=random.htm>random</a>,
+<a href=srandom.htm>srandom</a>,
+<a href=initstate.htm>initstate</a>,
+<a href=setstate.htm>setstate</a>,
+<pre>
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+<h3>GNU 18 May 1995 2
+</h3>
+
+ </pre>
+<P>
+<hr>
+<p>
+<center>
+<table border=2 width=80%>
+<tr align=center>
+<td width=25%>
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+
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