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 32  .\"     @(#)rand.3	8.1 (Berkeley) 6/4/93
 33  .\" $FreeBSD: src/lib/libc/stdlib/rand.3,v 1.16 2007/01/09 00:28:10 imp Exp $
 34  .\"
 35  .Dd May 25, 1999
 36  .Dt RAND 3
 37  .Os
 38  .Sh NAME
 39  .Nm rand ,
 40  .Nm rand_r ,
 41  .Nm srand ,
 42  .Nm sranddev
 43  .Nd bad random number generator
 44  .Sh LIBRARY
 45  .Lb libc
 46  .Sh SYNOPSIS
 47  .In stdlib.h
 48  .Ft int
 49  .Fo rand
 50  .Fa void
 51  .Fc
 52  .Ft int
 53  .Fo rand_r
 54  .Fa "unsigned *seed"
 55  .Fc
 56  .Ft void
 57  .Fo srand
 58  .Fa "unsigned seed"
 59  .Fc
 60  .Ft void
 61  .Fo sranddev
 62  .Fa void
 63  .Fc
 64  .Sh DESCRIPTION
 65  .Bf -symbolic
 66  These interfaces are obsoleted by
 67  .Xr arc4random 3 .
 68  .Ef
 69  .Pp
 70  The
 71  .Fn rand
 72  function computes a sequence of pseudo-random integers in the range
 73  of 0 to
 74  .Dv RAND_MAX
 75  (as defined by the header file
 76  .In stdlib.h ) .
 77  .Pp
 78  The
 79  .Fn srand
 80  function sets its argument
 81  .Fa seed
 82  as the seed for a new sequence of
 83  pseudo-random numbers to be returned by
 84  .Fn rand .
 85  These sequences are repeatable by calling
 86  .Fn srand
 87  with the same seed value.
 88  .Pp
 89  If no
 90  .Fa seed
 91  value is provided, the functions are automatically
 92  seeded with a value of 1.
 93  .Pp
 94  The
 95  .Fn sranddev
 96  function initializes a seed, using the
 97  .Xr random 4
 98  random number device which returns good random numbers.
 99  However, the
100  .Fn rand
101  function still remains unsuitable for cryptographic use.
102  .Pp
103  The
104  .Fn rand_r
105  function
106  provides the same functionality as
107  .Fn rand .
108  A pointer to the context value
109  .Fa seed
110  must be supplied by the caller.
111  .Sh SEE ALSO
112  .Xr arc4random 3 ,
113  .Xr random 3 ,
114  .Xr random 4
115  .Sh STANDARDS
116  The
117  .Fn rand
118  and
119  .Fn srand
120  functions
121  conform to
122  .St -isoC .
123  .Pp
124  The
125  .Fn rand_r
126  function is as proposed in the POSIX.4a Draft #6 document.