stdlib/rand.3

   1 .\" Copyright (c) 1990, 1991, 1993
   2 .\"     The Regents of the University of California.  All rights reserved.
   3 .\"
   4 .\" This code is derived from software contributed to Berkeley by
   5 .\" the American National Standards Committee X3, on Information
   6 .\" Processing Systems.
   7 .\"
   8 .\" Redistribution and use in source and binary forms, with or without
   9 .\" modification, are permitted provided that the following conditions
  10 .\" are met:
  11 .\" 1. Redistributions of source code must retain the above copyright
  12 .\"    notice, this list of conditions and the following disclaimer.
  13 .\" 2. Redistributions in binary form must reproduce the above copyright
  14 .\"    notice, this list of conditions and the following disclaimer in the
  15 .\"    documentation and/or other materials provided with the distribution.
  16 .\" 3. All advertising materials mentioning features or use of this software
  17 .\"    must display the following acknowledgement:
  18 .\"     This product includes software developed by the University of
  19 .\"     California, Berkeley and its contributors.
  20 .\" 4. Neither the name of the University nor the names of its contributors
  21 .\"    may be used to endorse or promote products derived from this software
  22 .\"    without specific prior written permission.
  23 .\"
  24 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34 .\" SUCH DAMAGE.
  35 .\"
  36 .\"     @(#)rand.3      8.1 (Berkeley) 6/4/93
  37 .\" $FreeBSD: src/lib/libc/stdlib/rand.3,v 1.12 2001/09/07 14:46:36 asmodai Exp $
  38 .\"
  39 .Dd May 25, 1999
  40 .Dt RAND 3
  41 .Os
  42 .Sh NAME
  43 .Nm rand ,
  44 .Nm srand ,
  45 .Nm sranddev ,
  46 .Nm rand_r
  47 .Nd bad random number generator
  48 .Sh LIBRARY
  49 .Lb libc
  50 .Sh SYNOPSIS
  51 .In stdlib.h
  52 .Ft void
  53 .Fn srand "unsigned seed"
  54 .Ft void
  55 .Fn sranddev void
  56 .Ft int
  57 .Fn rand void
  58 .Ft int
  59 .Fn rand_r "unsigned *ctx"
  60 .Sh DESCRIPTION
  61 .Bf -symbolic
  62 These interfaces are obsoleted by
  63 .Xr random 3 .
  64 .Ef
  65 .Pp
  66 The
  67 .Fn rand
  68 function computes a sequence of pseudo-random integers in the range
  69 of 0 to
  70 .Dv RAND_MAX
  71 (as defined by the header file
  72 .Aq Pa stdlib.h ) .
  73 .Pp
  74 The
  75 .Fn srand
  76 function sets its argument
  77 .Fa seed
  78 as the seed for a new sequence of
  79 pseudo-random numbers to be returned by
  80 .Fn rand .
  81 These sequences are repeatable by calling
  82 .Fn srand
  83 with the same seed value.
  84 .Pp
  85 If no
  86 .Fa seed
  87 value is provided, the functions are automatically
  88 seeded with a value of 1.
  89 .Pp
  90 The
  91 .Fn sranddev
  92 function initializes a seed using the
  93 .Xr random 4
  94 random number device which returns good random numbers,
  95 suitable for cryptographic use.
  96 .Pp
  97 .Fn rand_r
  98 provides the same functionality as
  99 .Fn rand .
 100 A pointer to the context value
 101 .Fa ctx
 102 must be supplied by the caller.
 103 .Sh SEE ALSO
 104 .Xr random 3 ,
 105 .Xr random 4
 106 .Sh STANDARDS
 107 The
 108 .Fn rand
 109 and
 110 .Fn srand
 111 functions
 112 conform to
 113 .St -isoC .
 114 .Pp
 115 The
 116 .Fn rand_r
 117 function is as proposed in the POSIX.4a Draft #6 document.