(split) LDP_man-pages: release ioctl.2 [JM:00378]

[linuxjm/LDP_man-pages.git] / draft / man3 / rand.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\"
.\" Modified 1993-03-29, David Metcalfe
.\" Modified 1993-04-28, Lars Wirzenius
.\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
.\" Modified 1995-05-18, Rik Faith (faith@cs.unc.edu) to add
.\"          better discussion of problems with rand on other systems.
.\"          (Thanks to Esa Hyyti{ (ehyytia@snakemail.hut.fi).)
.\" Modified 1998-04-10, Nicola'O^ Lichtmaier <nick@debian.org>
.\"          with contribution from Francesco Potorti <F.Potorti@cnuce.cnr.it>
.\" Modified 2003-11-15, aeb, added rand_r
.\"
.\" Japanese Version Copyright (c) 1997 YOSHINO Takashi all rights reserved.
.\" Translated 1997-01-21, YOSHINO Takashi <yoshino@civil.jcn.nihon-u.ac.jp>
.\" Updated 2000-09-24, Kentaro Shirakata <argrath@ub32.org>
.\" Updated 2005-03-15, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2008-08-08, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v3.05
.\"
.TH RAND 3 2008-08-29 "" "Linux Programmer's Manual"
.\"O .SH NAME
.SH ̾Á°
.\"O rand, srand \- random number generator.
rand, srand \- Íð¿ô¤òÀ¸À®¤¹¤ë´Ø¿ô
.\"O .SH SYNOPSIS
.SH ½ñ¼°
.nf
.B #include <stdlib.h>
.sp
.B int rand(void);
.sp
.BI "int rand_r(unsigned int *" seedp );
.sp
.BI "void srand(unsigned int " seed );
.fi
.sp
.in -4n
.\"O Feature Test Macro Requirements for glibc (see
.\"O .BR feature_test_macros (7)):
glibc ¸þ¤±¤Îµ¡Ç½¸¡ºº¥Þ¥¯¥í¤ÎÍ×·ï
.RB ( feature_test_macros (7)
»²¾È):
.in
.sp
.BR rand_r ():
_POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _POSIX_SOURCE
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O The
.\"O .BR rand ()
.\"O function returns a pseudo-random integer in
.\"O the range [0,\ \fBRAND_MAX\fR].
.BR rand ()
´Ø¿ô¤Ï [0,\ \fBRAND_MAX\fR] ¤ÎÈϰϤε¿»÷Íð¿ôÀ°¿ô¤òÊÖ¤¹¡£
.PP
.\"O The
.\"O .BR srand ()
.\"O function sets its argument as the seed for a new
.\"O sequence of pseudo-random integers to be returned by
.\"O .BR rand ().
.BR srand ()
´Ø¿ô¤Ï¡¢
.BR rand ()
´Ø¿ô¤Çºî¤é¤ì¤ëµ¿»÷Íð¿ôÀ°¿ô·ÏÎó¤Î¿·¤·¤¤¼ï¤È¤·¤Æ¡¢
¤½¤Î°ú¤­¿ô¤ÎÃͤò»ÈÍѤ¹¤ë¡£
.\"O These sequences are repeatable by calling
.\"O .BR srand ()
.\"O with the same
.\"O seed value.
¤³¤ì¤é¤Î´Ø¿ô¤ò»ÈÍѤ·¤Æºî¤é¤ì¤¿µ¿»÷Íð¿ô·ÏÎó¤Ï¡¢
Ʊ¤¸Ãͤò°ú¤­¿ô¤È¤·¤Æ
.BR srand ()
¤ò¸Æ¤Ö¤³¤È¤Ç¡¢
ºÆ¸½¤¹¤ë¤³¤È¤¬²Äǽ¤Ç¤¢¤ë¡£
.PP
.\"O If no seed value is provided, the
.\"O .BR rand ()
.\"O function is automatically
.\"O seeded with a value of 1.
¼ï¤ÎÃͤ¬Í¿¤¨¤é¤ì¤Ê¤¤¾ì¹ç¤Ë¤Ï¡¢
.BR rand ()
´Ø¿ô¤Ï
¼«Æ°Åª¤Ë 1 ¤ò¼ï¤È¤¹¤ë¡£
.PP
.\"O The function
.\"O .BR rand ()
.\"O is not reentrant or thread-safe, since it
.\"O uses hidden state that is modified on each call.
.\"O This might just be
.\"O the seed value to be used by the next call, or it might be something
.\"O more elaborate.
.\"O In order to get reproducible behavior in a threaded
.\"O application, this state must be made explicit.
.\"O The function
.\"O .BR rand_r ()
.\"O is supplied with a pointer to an
.\"O .IR "unsigned int" ,
.\"O to be used as state.
.BR rand ()
´Ø¿ô¤ÏºÆÆþ²Äǽ (reentrant) ¤Ç¤Ï¤Ê¤¤¡¢¤Ä¤Þ¤ê¥¹¥ì¥Ã¥É¡¦¥»¡¼¥Õ¤Ç¤Ï¤Ê¤¤¡£
¤Ê¤¼¤Ê¤é¡¢¤³¤Î´Ø¿ô¤Ï±£¤·¾õÂÖ¤ò»ý¤Ã¤Æ¤ª¤ê¡¢¸Æ¤Ó½Ð¤µ¤ì¤ëÅÙ¤ËÊѹ¹¤¹¤ë¤«¤é¤Ç¤¢¤ë¡£
¤Á¤ç¤¦¤É¤³¤Î±£¤·¾õÂÖ¤¬¼¡¤Î¸Æ¤Ó½Ð¤·»þ¤ÎÍð¿ô¤Î¼ï¤È¤·¤Æ»È¤ï¤ì¤ë¤è¤¦¤Ê¤â¤Î¤Ç¤¢¤ë¡£
¼ÂºÝ¤Ë¤Ï¤â¤¦¾¯¤·Ê£»¨¤«¤â¤·¤ì¤Ê¤¤¤¬¡£¥¹¥ì¥Ã¥É¤ò»ÈÍѤ¹¤ë¥¢¥×¥ê¥±¡¼¥·¥ç¥ó¤Ç
ºÆ¸½²Äǽ¤ÊÆ°ºî¤ò¤µ¤»¤¿¤¤¾ì¹ç¤Ë¤Ï¡¢¤³¤Î±£¤·¾õÂÖ¤¬¸¶°ø¤ÇºÆ¸½À­¤¬¤Ê¤¯¤Ê¤ë¡£
.BR rand_r ()
´Ø¿ô¤Ï
.I unsigned int
·¿¤ÎÊÑ¿ô¤Ø¤Î¥Ý¥¤¥ó¥¿¤ò°ú¤­¿ô¤Ë¤È¤ê¡¢
¤³¤ÎÊÑ¿ô¤ò¾õÂÖ³ÊǼÍѤ˻ÈÍѤ¹¤ë¡£
.\"O This is a very small amount of state, so this function will be a weak
.\"O pseudo-random generator.
.\"O Try
.\"O .BR drand48_r (3)
.\"O instead.
¾õÂÖ¿ô¤¬Èó¾ï¤Ë¾®¤µ¤¤¤Î¤Ç¡¢¤³¤Î´Ø¿ô¤Ï¤¢¤Þ¤ê¤è¤¤µ¼»÷Íð¿ôÀ¸À®´ï¤È¤Ï¸À¤¨¤Ê¤¤¤À¤í¤¦¡£
Âå¤ï¤ê¤Ë
.BR drand48_r (3)
¤ò»È¤¦¤È¤è¤¤¡£
.\"O .SH "RETURN VALUE"
.SH ÊÖ¤êÃÍ
.\"O The
.\"O .BR rand ()
.\"O and
.\"O .BR rand_r ()
.\"O functions return a value
.\"O between 0 and
.\"O .BR RAND_MAX .
.\"O The
.\"O .BR srand ()
.\"O function returns no value.
.BR rand ()
¤È
.BR rand_r ()
´Ø¿ô¤Ï 0 ¤È
.B RAND_MAX
¤Î´Ö¤Î¿ô¤òÊÖ¤¹¡£
.BR srand ()
´Ø¿ô¤ÏÃͤòÊÖ¤µ¤Ê¤¤¡£
.\"O .SH "CONFORMING TO"
.SH ½àµò
.\"O The functions
.\"O .BR rand ()
.\"O and
.\"O .BR srand ()
.\"O conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
.\"O The function
.\"O .BR rand_r ()
.\"O is from POSIX.1-2001.
´Ø¿ô
.BR rand ()
¤È
.BR srand ()
¤Ï SVr4, 4.3BSD, C89, C99, POSIX.1-2001 ¤Ë½àµò¤·¤Æ¤¤¤ë¡£
´Ø¿ô
.BR rand_r ()
¤Ï POSIX.1-2001 ¤ËͳÍ褹¤ë¡£
.\"O POSIX.1-2008 marks
.\"O .BR rand_r ()
.\"O as obsolete.
POSIX.1-2008 ¤Ï¡¢
.BR rand_r ()
¤òÇÑ»ßͽÄê¤È¤·¤Æ¤¤¤ë¡£
.\"O .SH NOTES
.SH Ãí°Õ
.\"O The versions of
.\"O .BR rand ()
.\"O and
.\"O .BR srand ()
.\"O in the Linux C Library use
.\"O the same random number generator as
.\"O .BR random (3)
.\"O and
.\"O .BR srandom (3),
.\"O so
.\"O the lower-order bits should be as random as the higher-order bits.
.BR rand ()
¤È
.BR srand ()
¤Î Linux C Library ÈǤϡ¢
.BR random (3)
¤È
.BR srandom (3)
¤Îξ´Ø¿ô¤ÈƱ¤¸Íð¿ôÀ¸À®
¥¢¥ë¥´¥ê¥º¥à¤ò»ÈÍѤ·¤Æ¤¤¤ë¡£¤½¤Î¤¿¤á¡¢²¼°Ì¤Î¥Ó¥Ã¥È¤Ï¾å°Ì¤Î¥Ó¥Ã¥È¤È
Ʊ¤¸¤¯¤é¤¤¤Ë¥é¥ó¥À¥à¤Ç¤¢¤ë¡£
.\"O However, on older
.\"O .BR rand ()
.\"O implementations, and on current implementations on different systems,
.\"O the lower-order bits are much less random than the higher-order bits.
.\"O Do not use this function in applications intended to be portable
.\"O when good randomness is needed.
.\"O (Use
.\"O .BR random (3)
.\"O instead.)
¤·¤«¤·¡¢µìÈǤÎ
.BR rand ()
¤Î¼ÂÁõ¤ä¡¢Â¾¤Î¥·¥¹¥Æ¥à¤Î¸½ºß¤Î¼ÂÁõ¤Ç¤Ï¡¢²¼°Ì¤Î¥Ó¥Ã¥È¤¬¾å°Ì¤Î¥Ó¥Ã¥È¤Û¤É
¥é¥ó¥À¥à¤Ë¤Ê¤Ã¤Æ¤¤¤Ê¤¤¡£°Ü¿¢À­¤ò¹â¤á¤ë¾ì¹ç¤Ç¤â¡¢ÀºÅ٤ι⤤Íð¿ô¤¬É¬ÍפÊ
¥¢¥×¥ê¥±¡¼¥·¥ç¥ó¤Ç¤Ï¤³¤Î´Ø¿ô¤Ï»ÈÍѤ·¤Æ¤Ï¤¤¤±¤Ê¤¤
(Âå¤ï¤ê¤Ë
.BR random (3)
¤ò»È¤¦¤³¤È)¡£
.\"O .SH EXAMPLE
.SH Îã
.\"O POSIX.1-2001 gives the following example of an implementation of
.\"O .BR rand ()
.\"O and
.\"O .BR srand (),
.\"O possibly useful when one needs the same sequence on two different machines.
POSIX 1003.1-2003 ¤Ç¤Ï¡¢
.BR rand ()
¤È
.BR srand ()
¤Î¼ÂÁõÎã¤È¤·¤Æ°Ê²¼¤òµó¤²¤Æ¤¤¤ë¡£¤³¤ì¤Ï¡¢°Û¤Ê¤ë£²¤Ä¤Î¥Þ¥·¥ó¤ÇƱ¤¸Íð¿ô·ÏÎó¤¬
ɬÍפʾì¹ç¤Ë¤ÏÊØÍø¤Ç¤¢¤í¤¦¡£
.sp
.in +4n
.nf
static unsigned long next = 1;

.\"O /* RAND_MAX assumed to be 32767 */
/* RAND_MAX ¤ò 32767 ¤È²¾Äê */
int myrand(void) {
    next = next * 1103515245 + 12345;
    return((unsigned)(next/65536) % 32768);
}

void mysrand(unsigned seed) {
    next = seed;
}
.fi
.in
.\"O .SH "SEE ALSO"
.SH ´ØÏ¢¹àÌÜ
.BR drand48 (3),
.BR random (3)